Do you know any switches which turns on/off based on day light?
I was just looking at light switches last night at Home Depot.  There's enough options to make your head spin.

Photosensitive light switches are mainly used for outdoor applications, but some look like they should do fine indoors if oriented properly.

Automatic Dusk to Dawn Light Control - Screws into a light socket

Photocell Light Control Indoor Plug-in - Plugs into an outlet