Quote:
Originally Posted by j.p.s
Do 4 lead, three die (R, G, B) LEDs count as white? They have been around for quite a while.
|
A regular "white" LED is blue or violet with one or more phosphors to give broad spectrum (colour rendition) so they can be used to illuminate.
An RGB LED only has narrow almost monochrome red, green and blue light. The relative red and blue adjusts the apparent colour temperature, but the colour rendition is absolutely terrible. Actually near monochrome yellow, orange, cyan, violets (rather than true magenta which is an illusion as it's a lack of green) etc will be the wrong colour or dark.
Quote:
|
White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device.
|
But the non-phosphor method is useless for room or street lights.
https://en.wikipedia.org/wiki/Light-...ode#White_LEDs
See Colour Rendition to understand why all viable commercial LED lights to replace incandescent or CFL etc uses phosphors.
Quote:
|
Numerically, the highest possible CIE Ra value is 100 and would only be given to a source whose spectrum is identical to the spectrum of daylight, very close to that of a black body (incandescent lamps are effectively black bodies), dropping to negative values for some light sources. Low-pressure sodium lighting has a negative CRI; fluorescent lights range from about 50 for the basic types, up to about 98 for the best multi-phosphor type. Typical white-color LEDs have a CRI of 80 or more, while some
|
A tri-colour R G B LED with no phosphors would be near zero CRI
Note that higher CRI (80 to 95) have lower efficiency than low CRI of 50.
https://en.wikipedia.org/wiki/Color_rendering_index
So an R G B LED source can be used for LCD backlights, and projectors onf any kind as those are not room illumination, but playing back a signal created by filtering the image to match the average human eye response to three channels, either R G B or brightness and two chroma channels. As the filterin was done at the camera or scanner, the display can use narrow R G B at approximately the peaks.
Pure R G B sources are terrible for actual general lighting.