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Author Topic: white l.e.d.s as a light source Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 03-23-2003 08:28 AM                     How about tri-color LEDs? They are coming out with all sorts of neat-o devices that have three (sets of) colored elements inside them. By varying the intensity of the three colors, any color can be made. I can't imagine that LEDs would be good enough for projection on anything but the smallest screen... If any. But I can imagine that LEDs would be a nice light source for small viewers. (Movieola style) Combine a small-screen viewer with the variable color LEDs and I imagine you would have a nice way for directors, editors and film technicians to judge the quality of scenes shot on film under different conditions of light. (Color temperature?) Question: If the words "Color Temperature" only apply to light generated from certain types of devices then wouldn't the words "Color Quality" (or something to that effect) be a better term for light that is not emitted from black body ratiators? (Just thinking...)  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 03-23-2003 10:42 AM                    Soitenly. But it's not going to be a single number when you've got some sort of strange curve.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 03-23-2003 12:16 PM                        "Color Rendering Index" is usually used to quantify the ability of a discontinuous spectrum light source to render colors accurately.  |  IP: Logged Bobby Henderson "Ask me about Trajan." Posts: 10973 From: Lawton, OK, USA Registered: Apr 2001 posted 03-23-2003 12:40 PM                     LEDs are costly and that alone would make them impractical for use as a light source where many thousands would be needed. We deal with LEDs a lot these days in indoor and outdoor electronic signs. They've all but replaced wedge based "light bulb" style lamps and the flipper type message centers are all gone. Lately, banks and schools with time/temperature signs or message centers with flipper based discs are needing them replaced with LED units when new maintenance issues arise. I would really love to see prices on the things take a dramatic drop. Then such items like full color outdoor video boards would lower into more practical price ranges. Right now customers must pay hundreds of thousands of dollars (or even millions of dollars) for large outdoor LED video displays. LEDs are costly, but when that cost is amortized out over the total maintenance cost of standard lighting the LEDs often win. This is why many new traffic signals and crosswalk lights are converting over to LED. LEDs last longer, with some rated for 10 years of life. But not really all that many LEDs are used for things like an LED cluster in a traffic light. Oh, and I do agree some of the newer LEDs are very bright.  |  IP: Logged Matt Hale Expert Film Handler Posts: 123 From: Vancouver, Canada Registered: Dec 2002 posted 03-23-2003 01:02 PM                        Well I have done a little more research and, unless I am not understanding something, it looks like it would only take 469 leds to equal the light output of a 1kw xenon. I have lost the links to the spec sheets, but as an exmaple, the Osram XBO1000 bulb has a rated light output of 3000 cd. The leds I am looking at are rated 6.4 cd apiece. That is significantly less leds than I thought it would take. Building the array out of seperate red green & blue diodes would definitely give you better control of the colour spectrum, and probably reduce the cost a bit. Where it would complictae matters is in ensuring that the light is sufficiently mixed before it hits the film that you do not have coloured blotches in the image. I have been trying to figure out what sort of lens(es) would be needed for this, and to convert the multiple beams from the many sources into one parallel beam, but I do not know enough about optics (like that wasn't obvious already.)  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 03-23-2003 03:59 PM                    While LEDs have made great inroads into signals and indicators I haven't seen them being used yet for general lighting although that may very well be next. I'm just mentioning that because I think you'd need to reach that point, where they are practical to produce a mass amount of light, and then be able to go beyond that and produce it in a way that is efficiently collectable. How boring an LED lamphouse would be!  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 03-23-2003 04:00 PM                     lets see that would be one awfully big "point source" so i doubt you could collect it very efficantly  |  IP: Logged Matt Hale Expert Film Handler Posts: 123 From: Vancouver, Canada Registered: Dec 2002 posted 03-23-2003 04:47 PM                        Check out http://pro.colorkinetics.com/showcase/ They make some very cool architectural lighting for various applications, including theatres. More general leds lights, including incandescent replacements, flourescent replacements, even streetlights, is at http://www.theledlight.com/120-VAC-LEDbulbs.html This stuff is coming very quickly. I remember hearing that BP (or maybe it was Shell) is going to convert all their gas stations to white led light.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 03-23-2003 08:12 PM                        Check out the new Organic Light Emitting Diode (OLED) technology from Kodak, coming soon to a digital display near you. http://www.kodak.com/US/en/corp/display/index.jhtml http://www.kodak.com/US/en/corp/display/kodakAndOEL.jhtml http://www.kodak.com/US/en/corp/display/overview.jhtml  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 03-23-2003 08:18 PM                     John I remember reading abut some organic memory simms that kodak was developing that was faster than any current computor memory  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 03-23-2003 08:49 PM                        All thinking humans have "organic memory", don't they? Link to Kodak R&D: http://www.kodak.com/US/en/corp/researchDevelopment/  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 03-23-2003 09:27 PM                    Finding a thinking human would be a problem there...  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 03-23-2003 09:32 PM                        At Los Alamos? Lots of non-military research now.  |  IP: Logged Christopher Seo Jedi Master Film Handler Posts: 530 From: Los Angeles, CA Registered: Jun 99 posted 03-24-2003 05:19 AM                     Steve made some good points earlier. What if the LEDs were engineered so that the R,G,B spectral emission peaks of the LEDs involved coincided with the spectral response peaks of the C,M,Y dyes in the film? Or, taken to the hypothetical extreme, what if only the peak wavelength for each dye were used as illumination, as with lasers? Would the projected image of a well-shot film look any less rich or vibrant? Granted, discrete spectra are bad for viewing real-life objects, but it would seem to be different for projection, where the "object" we are viewing is color dyes with precise spectral characteristics to which the discrete light source can be optimized. And lasers certainly make a good point source....  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 03-24-2003 07:06 AM                    Oh, "there" referred to the concept of finding a thinking human (!) in general not anyplace specific.  |  IP: Logged

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