# Calculating Spectral Power Distribution of White LED

• kaje
In summary, there are three main methods of producing white light from an LED, each with a slightly different spectrum. These methods include color mixing, using a UV LED with RGB phosphor, and using a blue LED with a yellow phosphor. While it is possible to have a continuous spectrum that appears white, the appearance of objects may vary due to metamerism. Unlike incandescent lamps, white LEDs do not follow Planck's law and therefore do not have a simple method for calculating their spectral power distribution.

#### kaje

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

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

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-...wer/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

## 1. What is spectral power distribution (SPD) and why is it important for white LED?

Spectral power distribution refers to the distribution of light energy across the visible spectrum. It is important for white LED because it determines the color quality of the light emitted, as well as its efficiency and energy consumption.

## 2. How is spectral power distribution of white LED calculated?

The spectral power distribution of white LED is calculated by measuring the intensity of light emitted at various wavelengths using a spectrometer, and then plotting the data on a graph. This graph shows the relative intensity of light at each wavelength and can be used to determine the SPD of the LED.

## 3. What factors affect the spectral power distribution of white LED?

The spectral power distribution of white LED can be affected by several factors, including the materials used in the LED, the design of the LED chip, and the phosphor coating used to convert blue light into white light. Environmental factors such as temperature and humidity can also affect the SPD of white LED.

## 4. How does the spectral power distribution of white LED impact its color rendering ability?

The spectral power distribution of white LED directly affects its color rendering ability, which is the ability to accurately reproduce colors. A balanced SPD that covers a wide range of wavelengths results in better color rendering, while a skewed or narrow SPD can lead to poor color rendering and color distortion.

## 5. Can the spectral power distribution of white LED be adjusted to improve its performance?

Yes, the SPD of white LED can be adjusted through various methods such as using different phosphor coatings, altering the LED chip design, or using filters to modify the light output. These adjustments can improve the color quality, efficiency, and overall performance of white LED.