In my device, the lighting tests were carried out with the help of the histogram.
I did it with my own software, but the same procedure can be done by obtaining images of the illuminated window and observing the histogram of the image.
In my opinion, the ideal lighting image should have a histogram consisting of three vertical lines (blue, green and red curves) superimposed. This would mean that all the pixels would receive the same light energy. The image should be a neutral light gray color throughout.
Obviously this situation is ideal and in practice impossible to achieve, but we must get as close to it as we can.
I have followed the following method:
First we turn on the lighting and leave it on long enough for the lamp to reach thermal equilibrium.
In this state, we take images of the illuminated window so that it covers the entire window but does not include borders or dark areas.
The exposure time was adjusted so that the peak of the histogram curves was around 200 (for an 8-bit color depth).
In these conditions, if we have a lamp with independent colors, we are adjusting the intensities of the colors until the three curves overlap.
My lamp does not have the latter, so I did it by adjusting the camera’s color gains.
The narrower the base of the curves, the better. If the base is wide, it would mean that there are many pixels that receive more or less light than the average, which would be at the peak.
This image is from the histogram of the light of my lamp, obtained under the aforementioned conditions.