And you've got to have enough light energy for it to actually do something. Shining a torch at the moon just isn't going to cut the mustard, much as setting off from England to drive to India with a teaspoon of petrol in your tank just isn't going to work. So just turning a light on in a room doesn't exactly create huge quantities of energy just bursting to get out and travel at a couple of hundred thousand miles a second. You really need a great big fucking electron beam to do that properly.