Agreed completely. As I said in the last bit: The proper solution is to put up proper lighting.
I can see this degenerating into some sort of efficiency metric that will be engineered around. For instance, it wouldn't be too hard to take the Google logo and make it a proper "light" with some LEDs. Or simply write out the name in white LEDs.
If you put a poster in front, the poster pays for the light.
Yeah I was purely viewing this from an environmental perspective, not an economical one. But you're right. This is of course the reason it's done that way.