# White LED

## Main Question or Discussion Point

Hi there, how one can compute the spectral power distribution of white LED ,i,e like black body radiator that has a formula of calculation..

regards

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Doug Huffman
Gold Member
A white LED is a composite. LED's emit single wavelength photons no one of which is white.

what I meant that the resulted spectrum of the combination ..does it have IR-radiation in that spectrum

CWatters
Homework Helper
Gold Member
Acording to Wikipedia there are at least three ways to make a "white" LED and all will have a slightly different spectrum.

http://en.wikipedia.org/wiki/Light-emitting_diode#Other_white_LEDs

There are three main methods of mixing colors to produce white light from an LED:
• blue LED + green LED + red LED (color mixing; can be used as backlighting for displays)
• near-UV or UV LED + RGB phosphor (an LED producing light with a wavelength shorter than blue's is used to excite an RGB phosphor)
• blue LED + yellow phosphor (two complementary colors combine to form white light; more efficient than first two methods and more commonly used)[91]
Because of metamerism, it is possible to have quite different spectra that appear white. However, the appearance of objects illuminated by that light may vary as the spectrum varies
The wiki article includes the spectrum for a white LED made using RGB LEDs...
http://en.wikipedia.org/wiki/Light-emitting_diode#mediaviewer/File:Red-YellowGreen-Blue_LED_spectra.png
and a white LED made using a Blue LED and a phosphor...
http://en.wikipedia.org/wiki/Light-emitting_diode#mediaviewer/File:White_LED.png

thanks,,as it is known for continuous spectrum that resulted from incandescent lamp,Planck law is employed to plot the spectral power distribution of such a source, but for the white LED I could not find a way to do the same as it is not treated as a black body radiator...thanks