[BIair]

I wonder what percentage of street lights actually have activity below them? What about a motion sensing light that has dual-brightness levels? A lower level when no pedestrian or car activity is detected, and a brighter level when it is. Not only would this save energy, and look very cool when a car drives down a deserted street as lights brighten in advance of it, but it could enhance security as late night prowlers would have attention attracted to them by neighbors and police.

[ytjohn]

Most of the lights near my towns exit ramp work off of light sensors (dusk to dawn style). There are a couple where the sensor is either too sensitive or angled incorrectly (so it picks up vehicle headlights). As your car approaches, the light turns off. It's rather disconcerting when it happens.

[ars]

That would be very annoying to people living nearby.

It could work for highway interchanges though.

[InclinedPlane]

Those already exist.