[Not math, but hopefully fun] Automotive lights: Besides the traditional yellowish white headlights, we're seeing cold white, and pale green, blue, pink, and lavender. Plus those annoying prismatic things. But crawling down I280 tonight, I was struck by the uniformity of the red in the miles of taillights stretching out before me. Both LED and conventional. Is there some strict spectral standard? Or does my color discrimination roll off fast at the red end? hgb>To a first approximation, today's "white" LED and today's "white" fluorescent light are the same: They both excite a fluorescent dye with a blue/ultraviolet light. They differ in how the blue/ultraviolet light is created. The visible "white" color (or color "temperature") is dependent upon the type of dye. The dyes can be made from "quantum dots", which can be engineered to have the appropriate spectrum. "White" light can also be made using 3-4 colored LED's (green LED's are less efficient, so you tend to need RGGB instead of just RGB); this is used in large LED billboards and for LED TV's. Since you need 2 G's anyway, you can use G's with 2 different wavelengths to get a wider "color gamut" -- RGG'B. There are some LED TV's that utilize this idea. There are now LED stage/studio lights whose colors can be computer-programmed for different colors using these combinations. I would speculate that white light made from LED's of individual colors _might_ be more efficient (in terms of electrical power) than the white light from downconverted UV, but I haven't been able to confirm this. My best guess is that downconverted UV is cheaper/simpler to use, because it requires only one type of bulb, and because it draws upon a century of fluorescent light technology. At 04:50 PM 12/3/2012, Warren Smith wrote: The news hype media is full of stuff about how David Carroll, prof. at Wake Forest Univ. in NC, has invented new wondrous lighting technology, environmentally friendly, efficient as LEDs and "at least twice as efficient as fl.tubes," but simpler and looks better, wholy solid state, simple, most any shape (sheets, rods, bent rods,...), glowing capacitor using magic nanoparticles embedded in plastic, no toxic mercury like fl.tube has, long lived (>10 years), will be commercialized with in 1 year. I tracked it to this press release http://news.wfu.edu/2012/12/03/taking-the-buzz-out-of-office-lights/ and this pre-paper of some ilk: http://www.sciencedirect.com/science/article/pii/S1566119912004831 What the media hype machine never mentioned in about 10 articles I saw, but is revealed in the latter document, is that they incorporate substantial amounts of Iridium and Indium. That sounds like an immediate major lose right there. -- Warren D. Smith Just today I daydreamed about making a platinum-iridium disk puzzle which people couldn't game thermally. --rwg