Emergent Density Maps

Large spaces like libraries tend to have absurd amounts of very diffuse lighting. Most of this light is unnecessary. What would be nice is to attach to every light a micro controller that senses movement and light levels. In the most basic case, it would only turn the light on if there was movement and the light already available was below a certain threshold.

More advanced versions could learn about how much movement there was during different times of day, and how long people hung around in that space.

This seems like a fairly basic idea, so it has probably already been tested and rejected because it's too distracting or for some other reason.