If you see a blinking red light, what is your first thought? That something is wrong and needs immediate attention. What about a steady blue light? Perhaps an on-off button on electronics.
Illumination allows for a quick and intuitive read of your solution making it easy for your operator to use the application efficiently.
However, illumination is not only about color and the length of the signal, but also about the placement, the size and intensity of the light source.