Saving Electricity?

I've always been taught to turn off lights when I don't need them. But, my brother told me that it kills a camera's battery if you switch it on and off often/rapidly. So maybe your Mom just heard something like that and applied it to lights.

I have no evidence or any actual proof, so take it as you will.

That actually helps the battery. I find that when my camera says "Low Battery" and auto-shuts off, turning it on then off again will make it work for a short period of time.

However, to Kevin, turning on and off a light bulb rapidly does in fact decrease it's lifespan, as evidence from my childhood experiences that doing so may make the light snap and the coil break. However, just turning it off on and off in normal circumstances will not do anything. Only in rapid succession...