LED white light

LEDs are not natural sources of white light: they emit almost monochromatic light.

There are two main ways of producing white LED light:

• Combining multiple monochrome LEDs (e.g. red, green and blue) to create an RGB system and obtain white light
• Applying a yellow phosphorus coating over the die of an LED with a short wavelength (blue or UV), obtaining white light from the sum of blue and yellow.

The second method is the most popular one, as allows for greater efficiency and a better color rendering compared to an RGB system. To obtain different color temperatures, you can vary the wavelength of the LED, the composition and the thickness of the phosphorus coating.

The choice to use white light in imaging applications should be limited to cases where a true chromatic response is really needed, obviously along with a color camera.

In all other cases, the use of white light affects the performance of the optical system, due to the chromatic aberrations that are inevitably generated and due to the loss of resolution of color sensors.