Light of different color temperatures is used to create a certain ambiance. The term color temperature comes from the light that a black material radiates when it is heated to a certain temperature. It is measured in degrees kelvin (k). It is the same thing as when you are saying something is red hot or white hot.

The question is how broad the range is the lamp should support. White LED's produced for general lighting are usually produced from 2700k up to 6000k. To get a broader range it is possible to use amber and red LED's on the low end or blue leds on the high end.

The hypothesis is that the lowest color temperature should be around 1850k to reproduce candle light and sunrise/sunset and on the highest temperature 6500k to reproduce daylight.

The proof of concept board will contain multiple channels with 2700k and 6000k leds. Testing should provide data whether this is enough.

Spectral color mixing

To get a specific color temperature we will mix the light from different LED's. Each LED has a spectral intensity, it outputs a certain amount of light at a certain wavelength.

Here i have overlay-ed the spectral intensity graphs of two different Wurth LED's, the 158301227 and the 158301260. Although these are relative charts you can get an idea what can be achieved. The resulting light output of these two LED's combined is what you get when you add their spectral intensities together. By varying the power to the different LED's we can vary the resulting spectral intensity.

When the peaks in spectral intensity are too far apart the resulting light will not be natural and will not look nice. An example is the "white" light from RGB LED's. It looks off because it is really just red green and blue light.

Next update will be about the test results of the color mixing.