LDR Grid + Smartphone = ? Answered
I've got an idea but I don't know what it can be used for, yet. Maybe you'll have some ideas for useful applications based on this concept.
The idea is to make a grid of LDRs which fits the size of a smartphone/tablet screen, write some code which draws a similar grid on the screen (or just switch images of that grid) so that each LDR will be affected by the light (and color) provided by each cell from the screen.