I think it is more for the same reason as why you don't only eat fat and nothing else. They hurt it not with concentrated light, but with filtered light through the coloured lens thingy that they say "Poisons" the light as they eat it. Guess if they get all the light spectrum they are happy having a nice balanced diet…

The bothering was supposedly cause of the red lens thingies they used. It filters the light a bit which as the picts described it "Poisoned" the light. Kind of like how you need a balanced diet to be healthy.

I really like the Random Number Angle.