> > It's reported that paintings from around 1890 which use the "Chrome > > Yellow" > > yellow pigment are at risk of rapid fading when LED lighting is used. I > > surmise (possibly incorrectly) that this is caused by the strong blue > > component in such lighting. > > http://rt.com/art-and-culture/news/van-goghs-changing-color-901/ I also wondered if the yellow from the LED phosphor happened to match Chrome Yellow especially well. [Ponders absorption and color aspects in mind. Decides this should not be the issue. But ...]. > I am never surprised when supposed experts who are trusted to care for > our most precious resources do such stupid things. Obviously the lesson > they learned with fluorescent lights many years ago did not stick. > Artwork is halogen-only, with UV-blocking filters. That is the standard > for galleries. You'd certainly think that they'd look at the high energy end of the spectrum. The trouble with phosphor LEDS in this context is that the blue is part of the necessary light to fool the brain into seeing white, and filtering is therefore not possible. With halogen light, filtering at the UV & blue end will move your color* temperature down somewhat and potentially move you off the black-body radiation line which we see as white. With LEDs it would just give you yellow:-). > Not to mention the horrible color rendition of todays LED lighting. It's > fine for a laundromat art show, but van Gogh, really? CRI (color rendering index) for the best LEDs is getting very good. This is still (AFAIK) subjectively assessed using test pictures - but I'd expect that they will or have got to where an eye model and light output curce would allow it to be computed. CRI =3D 100 =3D tungsten equivalent The following is 'out of my head' subjective based on modern LEDs. 90 =3D good enough for all but the very best 80 =3D entirely bearable for most tasks including reading. Color pictures somewhat off. 70 =3D still perfectly usable. Color cast is not evident until you think about it if you don't have to make colour decisions. 60 =3D Color cast obvious (usually blue cast with LEDs) but fine if you value maximum light per $ over color rendition. Perfectly OK for writing or study. Don't expect picture color s to be correct, even if they look OK. Field surveys show that in developing country use, people using LED lighting for night time business illumination (food stalls etc) will usually choose low CRI lights over high CRI if there is a useful gain in brightness for equal cost - as there usually is. For most purposes I personally much prefer "cool white" or similar to "warm white" high CRI lighting. I find a CCT*** (correlated colour* temperature) of about 5000-6000 K acceptable). Lumen output (apparent light energy) is a weighted curve with eye response included**. Most Phosphor LEDs use a blue emitter with various amounts of yellow phosphor to adjust the blue/yellow balance. Lumens per Watt improves as you shift towards blue. Color temperatures (equivalent black body temperature) of 6000 - 8000 Kelvin tend to give CRIs in the 60-70 range but substantially more light per $. Some manufacturers are now making LEDs with multiple phosphors or "light bulbs" with external multi-phosphor mixes illuminated by blue LEDs, or using multiple colors of LED die as the light source*. All these approaches are aimed at providing high CRI. * Separate RGB LEDs or other mixes were the standard means of producing white or other colors before Nichia 'changed the game' by inventing the brilliant but retrospectively obvious phosphor LED. ** Blue light has an extremely low eye response. So much so that whereas longer wavelength colors have output specified in lumens, blue LEDs are usually specified in milliWatts output This is also because blue LEDs tend to be used either as an energy source (eg for dental filling material curing) or as phosphor drivers to produce light at other wavelengths, and eye response is not of relevance in either case. A top Royal Blue LED will output more than 500 mW of light energy per Watt of DC input. Helps cooling :-). Russell McMahon * color =3D colour for we Antipodeans and those in the motherland. *** CCT Kelvin Black body temperature / Source | | 1800 Candle 2000 Sunrise / Sunset 2800 Incandescent 3200 Halogen 5600 Midday sun 6000-8000 increasing shade Wikipedia http://en.wikipedia.org/wiki/Color_temperature CCT & CRI demystified http://www.lowel.com/edu/color_temperature_and_rendering_demystified.html Adjustable color temperature display http://www.lrc.rpi.edu/education/learning/terminology/cct.asp CIE1931 chromaticity diagram with black body "white" line shown http://upload.wikimedia.org/wikipedia/commons/b/ba/PlanckianLocus.png --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .