It's interesting that people are real sticklers about turning off unnecessary lights. As you said, the electricity costs are negligible. Today's "bulbs" are either CFL or LED and they consume virtually zero electricity. But I still have this itch to turn each one of before going to sleep.
You're going to need 10 watts to light even a tiny room with a single bulb. You can run a raspberry Pi (not even really designed to be low power) on half of that.
If your house is so small you only need one bulb per room and has a couple of rooms (i.e., you live in an apartment), where the light is fove feet from you, nobody is going to market a product for that.
As the other responder said, you're still in for at a minimum 20 watts in a room for an actual house. Further, you pay for those watts again if there is AC (so more like 25-30 watts), the lights might not all be tied to the light switch, and they may not all be rooms you frequent. And then add on that rooms you don't frequent may still have incandescent bulbs in them because you stopped, like me, after replacing 20 or 30 bulbs and you're replacing the rest as they burn out.
