 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
| PhotoKB HomeDiscussion Groups Digital Photography Digital PhotoDSLR CamerasZLR CamerasPoint & Shoot CamerasFilm Photography 35 mmLarge FormatMedium formatDarkroomFilm and LabsOther EquipmentPhoto Technique Nature PhotographyPeople PhotographyTechnique GeneralGeneral Photo Topics General TopicsAustralian PhotographyUK PhotographyDirectoryPhoto Clubs |
Photo Forum / General Photo Topics / UK Photography / November 2004LED lights for filmmaking
Hello, I recently saw an advert for some LED lights for filmmaking. They looked perfect - very efficient, flicker-free, dimable from 0-100% etc. The problem is that they're extortionately priced. So now I want to make my own LED lights for use on film... Has anyone tried this? What should I be careful of? Can I vary the colour temperature of the lights by pushing more or less current through the LEDs? Even better - does anyone know of any LED lights suitable for film that I could buy off the shelf here in the UK? Here's my dream LED light: - dimmable from 0-100% with no change in colour temp (ultimately I'd like to build in a remote control so I can change dim the light whilst I'm looking through the viewfinder on my camera) - cheap! - highly efficient - stable and predictable colour temperature (it would be very cool if I could change the colour temp with a switch... my research into LEDs so far has hinted at the possibility of changing the colour temperature by increased in the current). Please do let me know your thoughts - any leads you can give me will be very well received Thanks, Jack "Daniel Kelly (AKA Jack)" wrote ... > I recently saw an advert for some LED lights for filmmaking. > They looked perfect - very efficient, flicker-free, dimable > from 0-100% etc. The problem is that they're extortionately > priced. Have you priced white and/or blue LEDs? I'm all for rolling my own equipment (working on a couple of ideas for compact flourescent), but the price and efficiency of white and blue LEDs isn't there yet, IMHO. > So now I want to make my own LED lights for use on film... > > Has anyone tried this? What should I be careful of? You haven't mentioned what KIND of lights you are talking about. A small "fill" light that fits in the accessory shoe on top of your camcorder is one thing. A 500W or 1000W equivalent elipsoid or fresnel is something else again. And a big soft-light is yet annother thing. IMHO, only a small, camera-mounted fill light might be practical at this time (if you have deep pockets). > Can I vary the colour temperature of the lights by pushing more > or less current through the LEDs? I would doubt it. LEDs don't produce light the same way as filament-based lamps. Even the range of output is relative limited. Full-range dimming can be done only by pulsing the LEDs and adjusting the pulse-width. If you do this at a high enough frequency, it appears to be "flicker-free". > Even better - does anyone know of any LED lights suitable > for film that I could buy off the shelf here in the UK? I have seen some theatrical lighting equipment that claims to have LED sources, but as you say, they are scandalously expensive. > Here's my dream LED light: > > - dimmable from 0-100% with no change in colour temp > (ultimately I'd like to build in a remote control so I can > change dim the light whilst I'm looking through the viewfinder > on my camera) With the price of the LEDs, the cost of the dimming parts of the circuit (power transistors, heat sinks, etc.) will seem cheap. > - cheap! Don't hold your breath. At least for a few more years. > - highly efficient I seem to recall something about big heat-sinks on the backside of the LED sources, and even fan cooling. Doesn't bode very well for efficiency if all that power is going into useless heat. > - stable and predictable colour temperature (it would be very > cool if I could change the colour temp with a switch... my research > into LEDs so far has hinted at the possibility of changing the > colour temperature by increased in the current). Doesn't seem likely. OTOH, people even make full-color image displays with LEDs by close-spacing red, green, and blue LEDs and pulse-width modulating them to produce any color you want. "white LEDs" are sometimes nothing but red, green, and blue LED chips in the same package. The colors combine to make what appears to be "white" to us exactly the same as color displays CRT, LCD, etc.) > Please do let me know your thoughts - any leads you can give > me will be very well received In the last year or so, there has been a lot of discussion of white LEDs and the circuits used to drive them from batteries over on the newsgroup news:alt.binaries.schematics.electronic Dunno about any of the other newsgroups you have cross-posted this to. At least this is my perception of the current state of the art. I would be happy to learn that there is better news. > I would doubt it. LEDs don't produce light the same way as > filament-based lamps. Even the range of output is relative > limited. Full-range dimming can be done only by pulsing the This is not the only way: I have previously built a voltage controlled current source for driving LEDs, which allows linear, full range dimming. However, for high powers, this is rather harder to do without the pulsing approace, due to the heat dissipated by the active devices. > LEDs and adjusting the pulse-width. If you do this at a high > enough frequency, it appears to be "flicker-free". Which should be quite easy. LEDs can be driven to very high frequencies easily. I've transmitted a few watts (infra red) at 20KHz (using a current source driver) with no trouble. I could have gone higher, but I settled on that frequency. >>Even better - does anyone know of any LED lights suitable >>for film that I could buy off the shelf here in the UK? > > I have seen some theatrical lighting equipment that claims to > have LED sources, but as you say, they are scandalously > expensive. LEDs are currently rather expensive, at about £10 per Watt. > I seem to recall something about big heat-sinks on the backside > of the LED sources, and even fan cooling. Doesn't bode very > well for efficiency if all that power is going into useless heat. At 90% efficiency, a 1KW source will give off 100W of heat. Consider how hot a 100W lightbulb becomes. You don't want your LEDs getting that hot. > Doesn't seem likely. OTOH, people even make full-color image > displays with LEDs by close-spacing red, green, and blue LEDs [quoted text clipped - 3 lines] > appears to be "white" to us exactly the same as color displays > CRT, LCD, etc.) I believe that some white LEDs operate by giving off blue light anc converting some to green and red using phosphors. Others work in teh manner you describe. I would expect that to be more efficient. -Ed  Signature(You can't go wrong with psycho-rats.) (er258)(@)(eng.cam)(.ac.uk) /d{def}def/f{/Times findfont s scalefont setfont}d/s{10}d/r{roll}d f 5/m {moveto}d -1 r 230 350 m 0 1 179{1 index show 88 rotate 4 mul 0 rmoveto} for /s 15 d f pop 240 420 m 0 1 3 { 4 2 1 r sub -1 r show } for showpage > > LEDs and adjusting the pulse-width. If you do this at a high > > enough frequency, it appears to be "flicker-free". [quoted text clipped - 3 lines] > current source driver) with no trouble. I could have gone higher, but I > settled on that frequency. Surely if you pulse the LEDs you'll get patterning on the picture due to the sequential nature of the scanning. For example, if you pulsed the LEDs at 15625 kHz (the line frequency of British TV) you'd get one half the picture black and the other half white, with the proportion of black to white varying with the mark:space ratio of the driving signal (ie the brightness of the light). The only way to avoid this would be to have lots of LEDs all firing from the same signal but each with a different phase difference. Maybe the best frequency is one that is a long way from a harmonic of the line frequency, so that any remaining patterning looks like a random dot crawl over the picture rather than a static pattern. Or do LEDs have a fairly long persistence - ie does the light continue for some time after the driving voltage is removed? If so, the effect of varying the mark:space ratio would be reduced if the frequency was chosen to be high enough to avoid significant flicker. What is the situation with xenon tubes used as TV lights? Are they pulsed with variable mark:space ratio or are they on continuously with the current varied to vary the brightness? In sci.engr.lighting E. Rosten <look@my.sig> wrote: >> I would doubt it. LEDs don't produce light the same way as >> filament-based lamps. Even the range of output is relative [quoted text clipped - 4 lines] > dimming. However, for high powers, this is rather harder to do without > the pulsing approace, due to the heat dissipated by the active devices. A switched-mode current source can use relatively small inductors to smooth the current to something approximating DC. Brilliant, thanks loads for all your ideas. There's a fantastic thred over here: http://www.dvxuser.com/cgi-bin/DVX2/YaBB.pl?board=Links;action=display;num=10712 61354;start=0 Thanks, Jack > "Daniel Kelly (AKA Jack)" wrote ... > > I recently saw an advert for some LED lights for filmmaking. [quoted text clipped - 77 lines] > At least this is my perception of the current state of the art. I > would be happy to learn that there is better news. > "Daniel Kelly (AKA Jack)" wrote ... >> I recently saw an advert for some LED lights for filmmaking. [quoted text clipped - 77 lines] > At least this is my perception of the current state of the art. I > would be happy to learn that there is better news. I saw a Beyonce video ("Crazy in love" maybe) with a rooftop, twilight scene with what looked like flat discs of white leds maybe a foot in diameter, a bit like continuous ring-flash giving flat lighting. I don't imagine the "non-flicker" is possible -about the only way to dim LEDs is to use PWM - just hope the frequency is very much greater than your line rate. I'd agree that such lights are not likely to be cheap - there were probably several hundred LEDs per disc/ My 2 cents P. [snip] >I don't imagine the "non-flicker" is possible -about the only way to dim >LEDs is to use PWM - just hope the frequency is very much greater than your >line rate. As has been stated before, LEDs can be dimmed with a continuous current. In this case there is no flicker from the LED. The trick is to make a variable current source with high efficiency. This is done all the time by using a PWM circuit inside the power converter and then smoothing (filtering) the current before it is applied to the load. You get a continuously variable, high efficiency current source that has very little modulation on its output - and hence no flicker. SignatureVic Roberts http://www.RobertsResearchInc.com To reply via e-mail: replace xxx with vdr in the Reply to: address or use e-mail address listed at the Web site. > I saw a Beyonce video ("Crazy in love" maybe) with a rooftop, twilight > scene with what looked like flat discs of white leds maybe a foot in [quoted text clipped - 7 lines] > > P. I didn't see the video but there is an old cinematographers trick to light up things like that without affecting the rest of the scene. Shoot though a glass sheet (semi silvered works better) at 45 degrees. Position a spotlight so that it gets reflected to the subject in the same line as the camera. Anything with a "3M Scotchlite" retroreflective surface will light up really bright. Peter > I saw a Beyonce video ("Crazy in love" maybe) with a rooftop, twilight > scene with what looked like flat discs of white leds maybe a foot in > diameter, a bit like continuous ring-flash giving flat lighting. Described by one of the regulars on rec.video.production a year or two ago. He made a large disk that fit around the lens and laid "light-rope" around in a spiral to create a large flat light for a special shot. > Hello, > [quoted text clipped - 23 lines] > Please do let me know your thoughts - any leads you can give me will be very > well received LEDs as film lights? Sounds highly intriguing. I thought that LEDs tended to produce fairly monochromatic light, whereas you'd want broad-spectrum white light for filming. Also, I can't imagine LEDs producing sufficient light to illuminate something more than a few millimetres away! > LEDs as film lights? Sounds highly intriguing. I thought that LEDs tended to > produce fairly monochromatic light, whereas you'd want broad-spectrum white > light for filming. Also, I can't imagine LEDs producing sufficient light to > illuminate something more than a few millimetres away! You're forgotting how frightening the higher-intensity LEDs can be. A couple of years ago, a story turned up about an LED-based theatre light that generated relatively little heat and was tuneable in colour (presumably three lighting components in varying amounts). If it was tuned well to your sensor it could provide light that looked /white/ but unlesss the individual LEDs were quite broad band, you'd still get crap colour rendition of things withing the field of lighting. I really wonder what the current state of the art is for these things. B FOLLOW UP settto uk.tech.broadcast, and not 9 groups > > LEDs as film lights? Sounds highly intriguing. I thought that LEDs > > tended to produce fairly monochromatic light, whereas you'd want > > broad-spectrum white light for filming. Also, I can't imagine LEDs > > producing sufficient light to illuminate something more than a few > > millimetres away! > You're forgotting how frightening the higher-intensity LEDs can be. > A couple of years ago, a story turned up about an LED-based theatre > light that generated relatively little heat and was tuneable in colour > (presumably three lighting components in varying amounts). If it was > tuned well to your sensor it could provide light that looked /white/ but > unlesss the individual LEDs were quite broad band, you'd still get crap > colour rendition of things withing the field of lighting. > I really wonder what the current state of the art is for these things. > B> Phil: The original poster may be confusing on-Camera LED assemblies designed for on-axis chromakey (in green or blue or I think white** at IBC this year) with full-spectrum lighting, which event he white ones don't supply, sincle they are effectively 'fluoescents' in their light output: eg starting from an basic excited UV via doped layers or coatings which emit at selected visible colours (like fluorescent tubes) to give a 'balanced' white - as long as you are not then using that light to analyse the colour composition of a scene 9as in a camera! ((unless exactly marching the RGB filter - but even then, it is unlikely to have any spread, but be 3 or 4 monochromatic sources.)) **used with directional (scoth-light?? or similar name) reflectant backgrounds, giving good chromakey or matte separation of subject to background - the efficiency coming also from the directional nature of the reflective material. (Which is a couple of hundred for a sqaure metre or 2?) SignaturePhil Spiegelhalter: Phil@fillin.co.uk ==== Technical Training for Broadcasters ===== *RE CUE Mobile DV Multi-Camera Production and Non-Linear Editing* > LEDs as film lights? Sounds highly intriguing. Those red or cyan washes used on the glass parts of the 'Watchdog' set are from LED sources. The fun bit is that the brightness is controlled by high frequency pulse-width modulation, so Daniel may have issues with anything fitted with a shutter, hint-hint ! Cheers, G. Signaturehttp://www.rat.org.uk gareth at lightfox dot plus dot com > "Daniel Kelly (AKA Jack)" <d.kellyNOSPAM@NOSPAM.ucl.ac.uk> wrote in > message news:cl5mu4$g2e$1@uns-a.ucl.ac.uk... [snip] > LEDs as film lights? Sounds highly intriguing. I thought that LEDs > tended to produce fairly monochromatic light, whereas you'd want > broad-spectrum white light for filming. Also, I can't imagine LEDs > producing sufficient light to illuminate something more than a few > millimetres away! Have you seen many light entertainment shows recently? LED based coloured effects lighting is everywhere these days. You can get strips of single LEDs in a row, single miniature parcan-style LED lamps, side lit panels and rows of LED discs. All of these can be cycled in colour under lighting controller control - usually using DMX data - allowing all sorts of multi-coloured effects. Pulsar Light are the main manufacturers I know of who do this stuff. Steve >> "Daniel Kelly (AKA Jack)" <d.kellyNOSPAM@NOSPAM.ucl.ac.uk> wrote in >> message news:cl5mu4$g2e$1@uns-a.ucl.ac.uk... [quoted text clipped - 14 lines] >data - allowing all sorts of multi-coloured effects. Pulsar Light are the >main manufacturers I know of who do this stuff. I've followed this thread with interest but not a little scepticism. There seems to have been lots of references to high power *display* LEDs. However, providing enough radiated light to give adequate illumination for video filming seems to me a different issue. LEDs are semiconductors, and semiconductors always have had serious problems with heat dissipation and can so easily burn out (all those fans on the chips in my PC - wow). To get the equivalent of (say) a 500 watt flood in a LED (or even an LED array) seems to be a bit of an extreme design concept and would seem to have limited practical offerings compared with conventional lighting units. SignatureTony Morgan http://www.camcord.info > I've followed this thread with interest but not a little scepticism. > There seems to have been lots of references to high power *display* [quoted text clipped - 3 lines] > heat dissipation and can so easily burn out (all those fans on the chips > in my PC - wow). Touch an ordinary filament torch bulb while it is working, and then one of those new high brightness white LEDs. Notice the difference. Filament lamps are about 5% efficient, which means that for every 100W of light, you have to dissipate nearly a couple of kilowatts of heat. I'm not sure what the efficiency of LEDs is, but torches that use them run for months, so it must be greater. I see no reason why scaling this up for film or TV lighting use wouldn't be possible, though producing acceptable colour rendition might be a different matter, as the colour separation mechanisms used in photography assume a uniform spectral characteristic of the light source. Rod. >> I've followed this thread with interest but not a little scepticism. >> There seems to have been lots of references to high power *display* [quoted text clipped - 10 lines] >efficiency of LEDs is, but torches that use them run for months, so it must >be greater. While I see from the link that they do indeed exist, I'd argue that efficiency should be tempered with cost ($4000 + with a lamp life of 2000 hours). If someone can afford the cost of buying, then they can sure afford the cost of the power to drive them :-) Laurence (with his theatrical antecedents) will perhaps have some insight into the relative cost of conventional lighting units. >I see no reason why scaling this up for film or TV lighting use wouldn't be >possible, though producing acceptable colour rendition might be a different >matter, as the colour separation mechanisms used in photography assume a >uniform spectral characteristic of the light source. I see that the spec from the link gives 6000K, so I'd assume that colour is not an issue. I also recall several years ago when tricolour LEDs were used in reflective colour spectrometers for the print industry, so I'd speculate that colour is an issue (or rather that any issues can be relatively easily worked-around). SignatureTony Morgan http://www.camcord.info >While I see from the link that they do indeed exist, I'd argue that >efficiency should be tempered with cost ($4000 + with a lamp life of [quoted text clipped - 3 lines] >Laurence (with his theatrical antecedents) will perhaps have some >insight into the relative cost of conventional lighting units. At the moment, LEDs are expensive. AS you saw from the link I quoted. But technology always comes down in price. > >While I see from the link that they do indeed exist, I'd argue that > >efficiency should be tempered with cost ($4000 + with a lamp life of [quoted text clipped - 6 lines] > At the moment, LEDs are expensive. AS you saw from the link I > quoted. But technology always comes down in price. I'm running a 42 LED array for a fill light right now. Works well and will run for a couple of days on a small LiON battery pack. I know of a guy running a 192 LED (about 12 Watts power consumption) array with good results. These are arrays that were purchased from LEDTronics and adapted for video use. Note that these are not 500 watt halogen equivalents. But with modern cameras, 500 watts may be overkill depending on the application. > I'm running a 42 LED array for a fill light right now. Works well and > will > run for a couple of days on a small LiON battery pack. I know of a guy > running a 192 LED (about 12 Watts power consumption) array with good > results. These are arrays that were purchased from LEDTronics and adapted > for video use. Can you give a part number (or description)? I didn't see anything on their website that jumped out as a prime candidate. Sorry for taking so long to reply but I've been off using the light at another exhibition. The part number is MR16-42-21W-014M This is the warm white medium beam width version. It fits nicely in a strip-light shell (just remove the bulb-holder from the transformer base) used to hold a halogen MR16 bulb. I use this at about 6-10 feet just to get the colors to pop a bit and to fill in the shadows from the ugly overhead lights always found in a large hall. It is not a room illuminator. I'm using it with either a Sony DSR-300 or a PD-150 and they don't require a lot of light. The power comes from a 12 volt LiON battery pack with a single alkaline C-sized cell in series to get me closer to the 14 volt max of the lamp. The light output difference between 12 and 14 volts is significant. Just don't go over 14.4 volts (auto battery voltage max) to avoid problems. And don't do as I did with the salesman's sample. I happened to have my NRG battery belt out for recharge and I was completely discharging it by running a VariLight Pro. I saw that and in a burst of inspiration, plugged his LED MR16 into the VariLight body. BAD IDEA. The pulsed output of the VariLight promptly smoked the LED drive circuitry. This LED package is not polarity sensitive and I think that's what went up in smoke. > > I'm running a 42 LED array for a fill light right now. Works well and > > will [quoted text clipped - 6 lines] > I didn't see anything on their website that jumped > out as a prime candidate. Check this site to get your creative juices flowing :-) http://www.superbrightleds.com/MR16_specs.htm There are a lot more led sources than I could have imagined. Google on, dude David > Check this site to get your creative juices flowing :-) > [quoted text clipped - 5 lines] > > David Light sources are one thing: ergonomically designed light instruments are another. At least these won't give you 3rd degree burns, right? >> Check this site to get your creative juices flowing :-) >> [quoted text clipped - 10 lines] > > At least these won't give you 3rd degree burns, right? That could be a plus >> >While I see from the link that they do indeed exist, I'd argue that >> >efficiency should be tempered with cost ($4000 + with a lamp life of [quoted text clipped - 16 lines] > Note that these are not 500 watt halogen equivalents. But with modern > cameras, 500 watts may be overkill depending on the application. Are you using the GDL002 FloodLED unit? Tell us how you are using it. On people? How far away? Using anything between the light and the subject? The difference between light levels on center and 20 degrees off the centerline seems substantial. How does that affect the way you use it? Steve King Hi all, I'm new here, having just stumbled across this thread by accident. One of the things I do is make and sell high-powered LED lights for night-time mountain bike racing, so I'm painfully familiar with their capabilities and limitations, and how to drive them, handle battery management and so on. I'm always interested in experimenting in new application areas, so I've read this discussion with interest. I know next to nothing about the requirements for lighting for films in terms of colour rendition and light output - I'm assume they're somewhat more stringent than for riding a bicycle! I'd quite like to put together a prototype to experiment with. What types of lights do people use currently? I suspect that starting at the lower-wattage end of the market is a reasonable thing to do: to match up to the light output of a 500W halogen would cost in the region of £500 just for the LEDs alone, before even starting on the necessary mechanical arrangements and driver electronics. My current product range is visible at http://www.solidlights.co.uk/ (I know that makes this almost a commercial posting, but since the products are aimed at an entirely different customer base, can I be excused?) Regards Chris > Hi all, > [quoted text clipped - 25 lines] > Regards > Chris I think you would be most likely to create something similar to a "soft Box". these lights provide a diffuse light ranging from very small (~ 4"x6") to very large (custom units built for shooting products can be 20' x 20' or bigger). These provide a flattering light source with soft shadows. We use 2 ranges of color temperature; "daylight" 5000-6000 degrees Kelvin, and "Tungsten" 2800-3200 Kelvin. 2800 would be used when matching typical household lights, while most film and video tungsten lights are rated around 3200. the upper "daylight" temperature is used when matching to natural light either when working outside, or matching daylight coming through a window. To be useful they would have to produce at least 30 foot-candles at about 6' distance. Preferred would be at least double that, and many of these types of light will produce much more than that, allowing them to be used from a greater distance. What you might consider building might be in the 4" to 15" range. Either intended for interview work or mounted to the camera as a fill light. They don't have to be square. Some are hemispheric, and others are in the shape of a stick. Here are a couple links to get you started. http://www.indiana.edu/~telecom/faculty/krause/Sum_T351/t351week3.html http://www.chimeralighting.com/products/video.html http://www.theasc.com/clubhouse/tricks/tip-rp1.htm http://www.photography-lighting.com/softboxes.html David > > Hi all, > > [quoted text clipped - 58 lines] > > David There is an LED light fixture on the market right now. Can't remember who made it but we used an LED "ring light" before. You know the circular fixture used around the lens for and "ring" type reflection in the eyes. In sci.engr.lighting Roderick Stewart <rjfs@escapetime.nospam.plus.com> wrote: >> I've followed this thread with interest but not a little scepticism. >> There seems to have been lots of references to high power *display* >> LEDs. However, providing enough radiated light to give adequate <snip> > Touch an ordinary filament torch bulb while it is working, and then one of > those new high brightness white LEDs. Notice the difference. Filament lamps > are about 5% efficient, which means that for every 100W of light, you have > to dissipate nearly a couple of kilowatts of heat. I'm not sure what the > efficiency of LEDs is, but torches that use them run for months, so it must > be greater. Actually not. LEDs are cooler because they have the heatsinks designed so they are cooler. If they are not cooler, they stop working. LEDs work very well at low powers. Bulbs don't. The current generation of white LEDs is about as efficient as a 500W conventional floodlight bulb. >In sci.engr.lighting Roderick Stewart <rjfs@escapetime.nospam.plus.com> wrote: >>> I've followed this thread with interest but not a little scepticism. [quoted text clipped - 16 lines] >The current generation of white LEDs is about as efficient as a 500W >conventional floodlight bulb. They are actually not quite that good. If you use the minimum guaranteed output instead of "typical" output and also correct for the fact that the junction will be hotter than 25C even if the case is held at 25C, (using the junction-to-case thermal resistance given by the manufacturer) you get an efficacy of about 15 to 17 lm/W for the best white LEDs available today. SignatureVic Roberts http://www.RobertsResearchInc.com To reply via e-mail: replace xxx with vdr in the Reply to: address or use e-mail address listed at the Web site. >Touch an ordinary filament torch bulb while it is working, and then one of >those new high brightness white LEDs. Notice the difference. Filament lamps >are about 5% efficient, which means that for every 100W of light, you have >to dissipate nearly a couple of kilowatts of heat. I'm not sure what the >efficiency of LEDs is, but torches that use them run for months, so it must >be greater. Filament lamps used for filming tend to be a lot more than 5% efficient - try at least 10%. A USA "standard" 100 watt 120V lightbulb, known as an A19, gets about 6.7%. High wattage halogens get a little more, and photographic lamps with short life expectancy get as much as 12%. Now for white LEDs: Really good ones get about 10%. I saw a couple figures in Nichia's website consistent with about 12%. As for LEDs of other colors: One manufacturer makes red ones that achieve about 25 and orange ones that achieve about 20%%, otherwise 20% for red and 10-15% for other colors is really good. As for heat: Ever see how much heatsinking a 5 watt Luxeon needs? One more thing: A majority of the energy going into a filament lamp becomes infrared and usually escapes. With LEDs, nearly enough all energy going in that fails to be converted to light (or wavelengths near those the LED is intended to produce) becomes non-radiant heat that has to be conducted out. - Don Klipstein (don@misty.com) In sci.engr.lighting Don Klipstein <don@manx.misty.com> wrote: <snip> > As for heat: Ever see how much heatsinking a 5 watt Luxeon needs? > One more thing: A majority of the energy going into a filament lamp > becomes infrared and usually escapes. With LEDs, nearly enough all energy > going in that fails to be converted to light (or wavelengths near those > the LED is intended to produce) becomes non-radiant heat that has to be > conducted out. Which is of course nice if you want a light with no infrared, but not much else. > Filament lamps used for filming tend to be a lot more than 5% efficient > - try at least 10%. A USA "standard" 100 watt 120V lightbulb, known as an > A19, gets about 6.7%. High wattage halogens get a little more, and > photographic lamps with short life expectancy get as much as 12%. That's a lot? Even fluorescent lights are only about 40% efficient aren't they? This is a great deal more than filament lamps, which is why they can save money in the home, but the efficiency of light sources in general is abyssmal, as it seems they all give out more heat than light. > Now for white LEDs: Really good ones get about 10%. I saw a couple > figures in Nichia's website consistent with about 12%. > As for LEDs of other colors: One manufacturer makes red ones that > achieve about 25 and orange ones that achieve about 20%%, otherwise 20% > for red and 10-15% for other colors is really good. Thanks for this info. I had thought that LEDs were better than this, but apparently not. There's certainly room for some serious improvement in this area. Rod. Snipped... >Thanks for this info. I had thought that LEDs were better than this, >but apparently not. There's certainly room for some serious improvement >in this area. I've been quite puzzled at the (reported here) high powers of current-technology LEDs It's many years ago now, but the last time I encountered LEDs at the sharp end was when the (then) high-powered LEDs first appeared. And to use them we had to replace our front panels with 1/4" aluminium precision drilled for a close LED fit to dissipate the heat. And this was in an indication application, not that of illumination of a subject. LEDs are, after all, semiconductors which are inherently prone to destruction by heat at the junction. Worse, the polymer resin that they're encapsulated in doesn't have very high thermal conductivity. SignatureTony Morgan http://www.camcord.info >Snipped... > [quoted text clipped - 10 lines] >precision drilled for a close LED fit to dissipate the heat. And this >was in an indication application, not that of illumination of a subject. When was this? Sometime around 1986, GaAlAsP red LEDs came onto the market. Those got plenty bright, almost bright enough to see in areas illuminated by direct sunlight, at currents low enough to take no special measures to dissipate heat from the LEDs. GaAlAsP has had an additional breakthrough and some evolution quadrupling its output and efficiency over the years into the mid 1990's. In the mid or late 1990's, InGaAsP gave us even brighter orange-red and orange LEDs and yelllow ones as bright as GaAlAsP in the same traditional indicator lamp packages. InGaN was put into use in the late 1990's to give us similarly bright blue, green and white LEDs. LEDs in packages that indicator lamp LEDs were made with since the 1970's have been used in flashlights for a few years now. Lumileds brought forth the first really popular high current heatsinkable LEDs just a few years ago. These had a maximum current of 350 mA and wattage of 1 to 1.2 watts. There are now higher power versions up to 5 watts. Cree, Nichia and others are now making 350 mA LEDs. - Don Klipstein (don@misty.com) I think that you should be comparing apples against apples (ie lumens/watt against lumens/watt). Here's an article which talks about the efficiency of flourescent bulbs and LEDs. http://members.misty.com/don/lede.html Basically it makes a general assumption that the efficiency of an LED is about twice that of a flourescent bulb. What it fails to talk about is the angle of light projection. LED's typically have a projection of 20 degrees. That simply means that most of the light power is focussed in a narrow beam (spot lighting). If you need to have a larger angle you will need more LEDs to cover the angles. This means that you'll need more power to get the equivalent lighting. The upshot is that LED's are more efficient "when and only when" they are used in spot lighting situations. Even then they are only about a 2 times more efficient. Also, the heat will still have to be dissipated (albeit half as much as a flourescent light source). > Snipped... > [quoted text clipped - 13 lines] > junction. Worse, the polymer resin that they're encapsulated in doesn't > have very high thermal conductivity. >I think that you should be comparing apples against apples (ie lumens/watt >against lumens/watt). [quoted text clipped - 6 lines] >Basically it makes a general assumption that the efficiency of an LED is >about twice that of a flourescent bulb. I don't claim that, athough I believe someone else does or some other people do. Really good white LEDs are nowadays about twice as efficient as many incandescents, but have efficiency (or more appropriately luminous efficacy) still not exceeding that of short-life photographic lamps. > What it fails to talk about is the >angle of light projection. LED's typically have a projection of 20 degrees. Or 15, or 30, or 45. Some have 60. Some have 110-120 or so. Some are really narrow - like less than 15! >That simply means that most of the light power is focussed in a narrow beam >(spot lighting). There are plenty of incandescents that also do this! > If you need to have a larger angle you will need more LEDs >to cover the angles. This means that you'll need more power to get the [quoted text clipped - 6 lines] >Also, the heat will still have to be dissipated (albeit half as much as a >flourescent light source). Heat dissipation from LED high power light sources is often a major problem, since they do not withstand high temperatures as well as incandescents do. And incandescents can toss away about or somewhat more than half their wasted power input as infrared, while with LEDs nearly all energy that does not become desired output becomes heat that materializes at the lamp(s)! - Don Klipstein (don@misty.com) > Really good white LEDs are nowadays about twice as efficient as many >incandescents, but have efficiency (or more appropriately luminous >efficacy) still not exceeding that of short-life photographic lamps. Don - can you please post the manufacturer and part number of such an LED? When I look at the data for the most efficient white LED that can be purchased, which are the Lumileds Luxeon III LEDs operating at 700 ma, and then adjust for minimum guaranteed output instead of "typical" output and adjust for maximum guaranteed operating voltage instead of "typical" operating voltage and finally calculate the junction temperature for a heat sink temperature of 25C and adjust for the decrease in output as a function of junction temperature I get an efficacy of slightly less than 16 lm/W, which is about the same efficacy as a normal 100-watt, 750-hour incandescent lamp. SignatureVic Roberts http://www.RobertsResearchInc.com To reply via e-mail: replace xxx with vdr in the Reply to: address or use e-mail address listed at the Web site. >> Really good white LEDs are nowadays about twice as efficient as many >>incandescents, but have efficiency (or more appropriately luminous >>efficacy) still not exceeding that of short-life photographic lamps. > >Don - can you please post the manufacturer and part number of such an >LED? Nichia NCCW022, of brightness rank Jc - the rank that includes the 42 lumen output mentioned in: http://www.nichia.co.jp/product/led-smd-powerled.html That web page mentions 42 lumens as some sort of typical, and the minimum for brightness rank Jc is 36. This is at case temperature of 25 C, as opposed to Lumileds specifying a junction temperature of 25 C, according to Nichia's datasheet. Voltage drop is typically 3.6 volts, max. for the upper-middle voltage rank drop is 4.0 volts, and max for the highest rank (worst) voltage drop is 4.3 volts. 36 lumens at 4.3 volts at .35 amp works out to... 23.9 lumens/watt This is a real worst case assuming you get the brightness rank that includes the lumen figure mentioned in the above-mentioned web page. "Typical" (maybe a bit optimistic for now) is 42 lumens at 3.6 volts at .35 amp, which works out to 33 lumens/watt. I would be a bit concerned about these figures being a bit optimistic because most of the major manufacturers appear to have been one-upping each other in their claims recently now that Cree is in the 350 mA white LED game. However, Cree has been advancing somewhat steadily at least their claimed blue LED chip performance over the years, so I expect white LED output to advance enough for the current claims to soon enough be conservative rather than optimistic. Optimistic would then be the next round of even higher claims for output and overall luminous efficacy. (Cree has a 350 mA white LED with output minimum 40 typical 45 lumens supposedly hitting production next month. I believe, based on the datasheet for the "dice" (chips) that I believe they use, that the voltage drop is typically 3.4, maximum 3.9 volts. This works out to luminous efficacy of minimum 29.3 "typically" 37.5 lumens/watt. This is one of their "XL7090" LED "lamps". Cree specifies ambient temperature of 25 degrees C for their current XL7090 products in http://www.cree.com/Products/lmp_7090.asp -?? specify ambient temperature rather than case temperature for a product that requires a heatsink??) >When I look at the data for the most efficient white LED that can be >purchased, which are the Lumileds Luxeon III LEDs operating at 700 ma, [quoted text clipped - 5 lines] >efficacy of slightly less than 16 lm/W, which is about the same >efficacy as a normal 100-watt, 750-hour incandescent lamp. Close to what I got for Luxeon III "star"... I figure about 16.1 lumens/watt if the worst case voltage drop decreases with increasing temperature the same as typical voltage drop does. With a thermal resistance of 17 degrees C per watt and 3.06 watts, junction temp. is 77 degrees C. Looks like you get 82% of the light output that you get with the junction temperature at 25 degrees C. The Luxeon III "emitter" has a thermal resistance of 13 degrees C per watt as opposed to 17 for the "star", making the worst case junction temperature slightly over 12 degrees C cooler, increasing light output slightly over 4% (and voltage drop .5-.6%) higher - let's say worst case overall luminous efficacy is 3.5% better than that of the "star", or 16.6 lumens/watt. Of course this assumes cooling the smaller heatsink surface of the "emitter" to 25 degrees C. I do not like the way Lumileds has their nominal performance specified at a junction temperature that requires a heatsink temperature of typically -19 degrees C (-2 degrees F) (for Luxeon III "star") if operated continuously. - Don Klipstein (don@misty.com) >>> Really good white LEDs are nowadays about twice as efficient as many >>>incandescents, but have efficiency (or more appropriately luminous [quoted text clipped - 10 lines] > That web page mentions 42 lumens as some sort of typical, and the >minimum for brightness rank Jc is 36. Good find, but this is not a the real minimum that a customer would find in an order of these devices. Nichia states on their data sheet for this LED: "One delivery will include up to two color ranks, four luminous flux ranks and three forward voltage ranks of the product. THE QUANTITY-RATIO OF THE RANKS IS DECIDED BY NICHIA." [Emphasis is mine.] So, the customer has no control at all over what rank LEDs he or she gets from Nichia and cannot design a product or application around the so-called minimum output of the Rank Jc device. They must assume that some, or perhaps all, of the devices they receive will be Rank Ja, which has only one half the performance of the Rank Jc devices. > This is at case temperature of 25 C, as opposed to Lumileds specifying a >junction temperature of 25 C, according to Nichia's datasheet. [quoted text clipped - 7 lines] > This is a real worst case assuming you get the brightness rank that >includes the lumen figure mentioned in the above-mentioned web page. No, the real worst case is about half your number, based on the assumption that any order would include some or all Rank Ja devices. > "Typical" (maybe a bit optimistic for now) is 42 lumens at 3.6 volts at >.35 amp, which works out to 33 lumens/watt. [quoted text clipped - 20 lines] >-?? specify ambient temperature rather than case temperature for a product >that requires a heatsink??) I find only typical output data given at the link you provide. I agree that the specifying ambient temperature is a bit confusing for a device that needs an additional heat sink. >>When I look at the data for the most efficient white LED that can be >>purchased, which are the Lumileds Luxeon III LEDs operating at 700 ma, [quoted text clipped - 26 lines] > > - Don Klipstein (don@misty.com) SignatureVic Roberts http://www.RobertsResearchInc.com To reply via e-mail: replace xxx with vdr in the Reply to: address or use e-mail address listed at the Web site. >> (Cree has a 350 mA white LED with output minimum 40 typical 45 lumens >>supposedly hitting production next month. I believe, based on the [quoted text clipped - 10 lines] >that the specifying ambient temperature is a bit confusing for a >device that needs an additional heat sink. Sorry, the 40 lumen minimum for the soon-to-come part is in this Cree press release: http://www.cree.com/News/news210.asp - Don Klipstein (don@misty.com) > Sorry, the 40 lumen minimum for the soon-to-come part is in this Cree >press release: > >http://www.cree.com/News/news210.asp > > - Don Klipstein (don@misty.com) Thanks Don. SignatureVic Roberts http://www.RobertsResearchInc.com To reply via e-mail: replace xxx with vdr in the Reply to: address or use e-mail address listed at the Web site. > LED's typically have a projection of 20 degrees. Think that's rather old. I've been using 60 degree ones to replace indicator lamps in switches that were forever blowing. Signature*There are two kinds of pedestrians... the quick and the dead. Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. >> Filament lamps used for filming tend to be a lot more than 5% efficient >> - try at least 10%. A USA "standard" 100 watt 120V lightbulb, known as an [quoted text clipped - 5 lines] >save money in the home, but the efficiency of light sources in general is >abyssmal, as it seems they all give out more heat than light. I think 40% is high side in a good case for fluorescents, and I have some doubts even then. I think more like 30% for a really good one that produces white or whitish light. However, fluorescents do have one other advantage for "overall luminous efficacy": Phosphors can be selected with spectra better matched to the spectral response of the human eye than the spectra of daylight, incandescent, or "black body" radiation are. As one example, the reddish phosphor in triphosphor fluorescents produces an orange-red wavelength that the eye is more sensitive to than to most other red wavelengths. As a result, if a given fluorescent lamp is 3 times as efficient as a given incandescent lamp at converting electricity to light, then its "overal luminous efficacy" (lumens out per watt in) can be close to 4 times that of the incandescent. Yes, light sources are maddeningly inefficient. LEDs are advancing, but hardly anyone expects them to surpass fluorescent lamps in efficiency of producing white light anytime soon. I have heard of efficiency well over 50% for an underpowered low pressure sodium lamp in an oven - assuming you don't count the energy/power used to heat the oven. Low pressure mercury (as in a fluorescent lamp minus the phosphor) can reach/exceed 50% efficiency in producing the shortwave UV that excites fluorescent lamp phosphors, but the phosphors have a major loss. - Don Klipstein (don@misty.com) Sorry, I forgot to mention another "percieved" issue with LED light sources. Due to the optical nature of the human eye, LED's appear to be brighter than a broad beam light source (a bulb) because of the narrow beam nature of an LED. What this does is saturate the rods in the back of the eyes and hence the appear to be brighter. What you will notice though is that an LED will leave a small spot on your retina (when you close your eyes you'll see the negative image) whereas a bulb will leave a larger spot. Basically the angular concentration of light is higher for an LED and as a result it appears brighter. >>Touch an ordinary filament torch bulb while it is working, and then one of >>those new high brightness white LEDs. Notice the difference. Filament [quoted text clipped - 24 lines] > > - Don Klipstein (don@misty.com) > Sorry, I forgot to mention another "percieved" issue with LED light sources. Entirely appropriate quotes, as it happens. > Due to the optical nature of the human eye, LED's appear to be brighter than > a broad beam light source (a bulb) because of the narrow beam nature of an > LED. What this does is saturate the rods in the back of the eyes and hence > the appear to be brighter. Psycho-optical mumbo-jumbo. How can an effect that *prevents you perceiving the full brightness of something* cause it to appear brighter? > What you will notice though is that an LED will > leave a small spot on your retina (when you close your eyes you'll see the > negative image) whereas a bulb will leave a larger spot. An effect which does not require saturation. > Basically the angular concentration of light is higher for an LED and as a > result it appears brighter. *raised eyebrow* Unless you're extremely close to the light, this has nothing to do with the narrow-beam nature of the LED. You may be talking about size of the emitting area, but a lot of small bulbs have filaments similar inside to a typical LED, even before you add the magnifying lens on the front of most LEDs. B In sci.engr.lighting Bruce Murphy <pack-news@rattus.net> wrote: >> Sorry, I forgot to mention another "percieved" issue with LED light sources. > [quoted text clipped - 8 lines] > perceiving the full brightness of something* cause it to appear > brighter? Because it might be much brighter, hence need an aversion response to save the sight. > In sci.engr.lighting Bruce Murphy <pack-news@rattus.net> wrote: > > [quoted text clipped - 13 lines] > Because it might be much brighter, hence need an aversion response to > save the sight. It might well, but *how can it appear brighter*. B In sci.engr.lighting Bruce Murphy <pack-news@rattus.net> wrote: >> In sci.engr.lighting Bruce Murphy <pack-news@rattus.net> wrote: >> > [quoted text clipped - 15 lines] > > It might well, but *how can it appear brighter*. Because the brain is wired to safeguard vision. > In sci.engr.lighting Bruce Murphy <pack-news@rattus.net> wrote: > >> > Psycho-optical mumbo-jumbo. How can an effect that *prevents you > >> > perceiving the full brightness of something* cause it to appear [quoted text clipped - 6 lines] > > Because the brain is wired to safeguard vision. Irrelavnt. If we look at the post in question both the incandescent and LED sources were implied (thanks to the other serious misconceptions) to saturate the eye. Now, given that there is *no more detector range available* how can one appear 'brighter' than the other? This is a comparitive, not whether it appears bright or not, or even whether there is an aversion response to it. You can't handwave and say 'because the brain is hardwired that way' becuase under the circumstances that the OP described, there is no remaining capacity to make that judgement. That's what saturated means. B > Irrelavnt. If we look at the post in question both the incandescent > and LED sources were implied (thanks to the other serious [quoted text clipped - 9 lines] > remaining capacity to make that judgement. That's what saturated > means. OTOH, you can't argue with your own brain and iris. OK, what I was trying to say is the apparent brightness actually seems brighter because there *is* saturation of the rods. Now, with the eyes and the way in which the rods work, brightness is actually a perception between the ilumnation of some rods versus other rods. If most of the rods are in dakness and some of the rods are saturated, the saturated rods will send the message to the brain that the light source is very bright. With a larger dispersion of light (ie a wide beam) the apparent brightness seems to be less as there is less of a distinction between the rods. Apparent brighness is the difference between 2 intensities. It is not absolute. >> Irrelavnt. If we look at the post in question both the incandescent >> and LED sources were implied (thanks to the other serious [quoted text clipped - 11 lines] > > OTOH, you can't argue with your own brain and iris. >OK, what I was trying to say is the apparent brightness actually seems >brighter because there *is* saturation of the rods. [quoted text clipped - 9 lines] >Apparent brighness is the difference between 2 intensities. It is not >absolute. Not to be too nit-picky here, but I think you mean "cones" instead of "rods". The rods are only used at very low light levels, and are pretty much only in peripheral vision. The 3 (or so) types of cones are used for color vision and are packed into the fovea where you would be registering a small spot. Best regards, Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis www.daqarta.com > The 3 (or so) types of cones are used for color vision and > are packed into the fovea where you would be registering > a small spot. Most people have three types. Some women have four - which is probably why you get arguments about whether that dress/tie/whatever is blue or green. Yes seriously! ;-) SignatureJohn Cartmell john@ followed by finnybank.com FAX +44 (0)8700-519-527 Qercus magazine & FD Games www.finnybank.com www.acornuser.com Qercus - a fusion of Acorn Publisher & Acorn User magazines > > The 3 (or so) types of cones are used for color vision and > > are packed into the fovea where you would be registering > > a small spot. > > Most people have three types. Some women have four - which is probably why > you get arguments about whether that dress/tie/whatever is blue or green. I've come across this claim before. Do you have a reference for it? B > > > The 3 (or so) types of cones are used for color vision and are > > > packed into the fovea where you would be registering a small spot. > > > > Most people have three types. Some women have four - which is probably > > why you get arguments about whether that dress/tie/whatever is blue or > > green. > I've come across this claim before. Do you have a reference for it? It was reported in New Scientist sometime over the last couple of months or so. SignatureJohn Cartmell john@ followed by finnybank.com FAX +44 (0)8700-519-527 Qercus magazine & FD Games www.finnybank.com www.acornuser.com Qercus - a fusion of Acorn Publisher & Acorn User magazines > > > > The 3 (or so) types of cones are used for color vision and are > > > > packed into the fovea where you would be registering a small spot. [quoted text clipped - 7 lines] > It was reported in New Scientist sometime over the last couple of months or > so. So 'no' then :) B > > > > > The 3 (or so) types of cones are used for color vision and are > > > > > packed into the fovea where you would be registering a small [quoted text clipped - 8 lines] > > It was reported in New Scientist sometime over the last couple of > > months or so. > So 'no' then :) Shan't! ;-) You'd accept a reference if I gave you an issue but not page. This way you could still easily search the on-line index for NS and find the article. SignatureJohn Cartmell john@ followed by finnybank.com FAX +44 (0)8700-519-527 Qercus magazine & FD Games www.finnybank.com www.acornuser.com Qercus - a fusion of Acorn Publisher & Acorn User magazines >> > > > > The 3 (or so) types of cones are used for color vision and are >> > > > > packed into the fovea where you would be registering a small [quoted text clipped - 15 lines] >You'd accept a reference if I gave you an issue but not page. This way you >could still easily search the on-line index for NS and find the article. I subscribe to NS and I don't recall anything on the subject. So I did a search at: http://archive.newscientist.com/ and there's nothing there. Tomorrow, just to be sure, i'll dig out old copies of NS from my loft. It's so easy to claim attributes, but when it's so easily disconunted it seems foolish to do so (not that I disbelieve you). > > > The 3 (or so) types of cones are used for color vision and are > > > packed into the fovea where you would be registering a small spot. > > > > Most people have three types. Some women have four - which is probably > > why you get arguments about whether that dress/tie/whatever is blue or > > green. > I've come across this claim before. Do you have a reference for it? I've been stung into double checking and time is going faster than I imagined! New Scientist vol 181 issue 2432 31 January 2004 page 40 Colour is detected by millions of cone cells in the retina and in a normal person there are three types, responding to red, green and blue light. This makes humans trichromatic and in theory allows us to distinguish between more than 2 million different colours. Blue cones are very uniform but there are at least four versions of the gene that encodes the red visual pigment and four versions of the green. Because these genes are carried on the X chromosome, and men have only one X chromosome, the variant genes are readily expressed in men and often lead to subtle impairments in colour vision. But these variants don't just cause defects - they may give some women enhanced colour vision. Because women have two X chromosomes, it is possible for one X to carry the normal genes and the other to carry one or other of the variants. This means some women have an extra type of cone, making them potentially tetrachromatic. Deeb has now begun research on these super-sighted women and says the phenomenon may not be unusual. "Around 15 per cent of women are carriers of colour vision deficiency," he says. "Looking at 43 of these, two showed evidence of tetrachromacy." Samir Deep is at Columbia University, New York SignatureJohn Cartmell john@ followed by finnybank.com FAX +44 (0)8700-519-527 Qercus magazine & FD Games www.finnybank.com www.acornuser.com Qercus - a fusion of Acorn Publisher & Acorn User magazines > > > > The 3 (or so) types of cones are used for color vision and are > > > > packed into the fovea where you would be registering a small spot. [quoted text clipped - 9 lines] > > New Scientist vol 181 issue 2432 31 January 2004 page 40 thank you :) Now I'm going to tootle down to the library and see whether I can find any references for it. In my defence my 'so "no" then' was more to do with New Scientists breathlessness before accuracy editorial policy than anything else. B >>>> Most people have three types. Some women have four - which is >>>> probably why you get arguments about whether that >>>> dress/tie/whatever is blue or green. >> New Scientist vol 181 issue 2432 31 January 2004 page 40 > Now I'm going to tootle down to the library and see whether I > can find any references for it. Google for "Looking for Madam Tetrachromat" and "tetrachromacy". The story about scientists looking for (or testing and studying) possible tetrachromats - which, as suggested by genetic research, should all be women - was published in several magazines some 4 or 5 years ago. I read the original article (by Glenn Zorbette) from Red Herring, but it has been reprinted elsewhere, for example: <http://www.freerepublic.com/forum/a3a24199b1ef8.htm> <http://www.cs.utk.edu/~evers/documents/tetraChromat.txt> Signatureznark > Google for "Looking for Madam Tetrachromat" and "tetrachromacy". The > story about scientists looking for (or testing and studying) possible [quoted text clipped - 6 lines] > <http://www.freerepublic.com/forum/a3a24199b1ef8.htm> > <http://www.cs.utk.edu/~evers/documents/tetraChromat.txt> I found the following article somewhat more detailed and interesting. http://www.rmki.kfki.hu/~lukacs/TETRACH.htm B >> The 3 (or so) types of cones are used for color vision and >> are packed into the fovea where you would be registering >> a small spot. > >Most people have three types. Some women have four - which is probably why >you get arguments about whether that dress/tie/whatever is blue or green. Not to mention all the dichromats (color-blind) viewers of the world. There is an additional phenomenon recently described/proposed by my old friend Angela Brown. Seems the blue cones are easily damaged by UV exposure, which gives old vision a brownish tint (called "brunescence"). She and her co-author noted that in equatorial countries (lots of UV exposure) there tends to be be little or no distinction between shades of blue... most of the languages in those countries tend to call all bluish colors by the same general name, which translates to something like "dark" in each language. Tests on subjects show that they do indeed have significant brunescence by early adulthood, comparable to 90-year-old outdoor workers in northern regions. She has a demo of what the differences look like with and without this brunescence, and it's pretty dramatic. Unfortunately, it's not available on the Web anywhere... you have to attend one of her talks to see it, at the moment. Best regards, Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis www.daqarta.com <snip> >There is an additional phenomenon recently described/proposed >by my old friend Angela Brown. Seems the blue cones are easily >damaged by UV exposure, which gives old vision a brownish tint >(called "brunescence"). CORRECTION: Brunescence is not due to damage to the blue cones, but rather to damage to the lens. (I'd guess that might even protect the blue cones, by restricting the light reaching them.) "Senescence" is due to damage to little grey cells that make me forget these critical details! >She and her co-author noted that in >equatorial countries (lots of UV exposure) there tends to be be [quoted text clipped - 9 lines] >anywhere... you have to attend one of her talks >to see it, at the moment. Sorry for any confusion my senescence may have caused! Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis www.daqarta.com >Sorry, I forgot to mention another "percieved" issue with LED light sources. > >Due to the optical nature of the human eye, LED's appear to be brighter than >a broad beam light source (a bulb) because of the narrow beam nature of an >LED. Actually, the reason is small light source size. Consider a smallish welding arc the size of a smaller-than-average pea which may produce less light than a fluorescent fixture with four 4-foot lamps ("bulbs"). > What this does is saturate the rods in the back of the eyes and hence >the appear to be brighter. Separate issue - in favor of bluer light sources including most white LEDs over "warmer color" light sources. Wavelengths from mid-blue to mid-green (roughly 460-530 nm) are good for stimulating rods. Light with more of these wavelengths can have extra perceived "illuminating power" compared to light that has less of these wavelengths. Such an effect is greater in peripheral vision than in central vision, and is greater in dimmer illumination conditions where the function of the rods is more significant and less in brighter illumination conditions. This also makes cooler color compact fluorescents look better - but for room lighting illumination at lower level with cooler color easily appears "dreary gray". - Don Klipstein (don@misty.com) >Sorry, I forgot to mention another "percieved" issue with LED light sources. > [quoted text clipped - 7 lines] >Basically the angular concentration of light is higher for an LED and as a >result it appears brighter. Yes, concentrating the output of a light source will produce higher brightness when the beam is directed into the human eye, but to light a space we need lumens, not "brightness." Many LED manufacturers only provide data on brightness on their data sheets - only a few LED manufacturers provide data on total output in lumens. SignatureVic Roberts http://www.RobertsResearchInc.com To reply via e-mail: replace xxx with vdr in the Reply to: address or use e-mail address listed at the Web site. Agreed. Lumens over a certain angle also. Spot lights and wide beam lights of the same lumens values will have a different lighting effect. The light reflected will be more concentrated in the narrower beam lights. >>Sorry, I forgot to mention another "percieved" issue with LED light >>sources. [quoted text clipped - 17 lines] > provide data on brightness on their data sheets - only a few LED > manufacturers provide data on total output in lumens. anyone got a link to these leds? leslie In sci.engr.lighting "Daniel Kelly \(AKA Jack\)" <d.kellyNOSPAM@nospam.ucl.ac.uk> wrote: > Hello, > [quoted text clipped - 5 lines] > Has anyone tried this? What should I be careful of? Can I vary the colour > temperature of the lights by pushing more or less current through the LEDs? Generally no. No. > Even better - does anyone know of any LED lights suitable for film that I > could buy off the shelf here in the UK? Many. > Here's my dream LED light: > > - dimmable from 0-100% with no change in colour temp (ultimately I'd like to > build in a remote control so I can change dim the light whilst I'm looking > through the viewfinder on my camera) Not a problem. > - cheap! Extreme problem. Expect to pay well over 3 quid a watt, in quantity. > - highly efficient Nope, about as good as halogen bulbs, maybe a bit more if you go with mixed colours of LEDs, but then you run into new problems. > - stable and predictable colour temperature (it would be very cool if I > could change the colour temp with a switch... my research into LEDs so far > has hinted at the possibility of changing the colour temperature by > increased in the current). It alters, but generally not in useful ways. > Please do let me know your thoughts - any leads you can give me will be very > well received Wait a decade or two. Trimmed crosspost abit because server will think its spam... Hi from sci.engr.lighting > Hello, > > I recently saw an advert for some LED lights for filmmaking. They looked > perfect - very efficient, flicker-free, dimable from 0-100% etc. The > problem is that they're extortionately priced. So now I want to make my own > LED lights for use on film... Efficent ,er, um, see rhose MR16s your using at the moment, theyre probably abit more efficient.. > Has anyone tried this? What should I be careful of? Can I vary the colour > temperature of the lights by pushing more or less current through the LEDs? Not really, whites because theri blue with a phosphor go a bit of angry blue when you overdrive them though.... > Even better - does anyone know of any LED lights suitable for film that I > could buy off the shelf here in the UK? Sure I saw Kino Flo with some protype Luxeon LED film lights a while back, but then they make fluro compact film lights which fro general light are probably still a better bet. > Here's my dream LED light: > > - dimmable from 0-100% with no change in colour temp (ultimately I'd like to > build in a remote control so I can change dim the light whilst I'm looking > through the viewfinder on my camera) Thats kind of doable , but current white LEDs are basic phosphor wise,with a high colour temperature and not great Colour Rendering Index. RGB colour mixing does not give a good white , some units have started using RGB and Amber to warm it up a bit. > - cheap! cheap or bright? cannae have both > - highly efficient If you don`t need alot of light, say an LED macro ring it is efficient for the purpose, as replacement Redhead, not yet. > - stable and predictable colour temperature (it would be very cool if I > could change the colour temp with a switch... my research into LEDs so far > has hinted at the possibility of changing the colour temperature by > increased in the current). Going cooler CT wise in white, but cooking LED in practice, lowering efficiency, LEDs hit sweet spot at exceedingly low currents Negative temp co-efficient means output goes down as heat goes up Lowering lumen maintenace , cooked phosphors and LED dice put out less light as they age, hard life will age them faster > Please do let me know your thoughts - any leads you can give me will be very > well received http://www.ledmuseum.org/ http://members.misty.com/don/ HTH Adam > Thanks, > Jack "Daniel Kelly (AKA Jack)" wrote ... > I recently saw an advert for some LED lights for filmmaking. They looked > perf |
Enable EMail Alerts
Start New Thread
Reply to this Message