So it's possible to make a photo sensitive switch. It's also possible to make a dimmer that gets brighter as ambient light increases, but what about a dimmer that gets brighter as light decreases. I want to do this to control a joule thief, or self regulating oscillator. So the brightness of the LED stays at the point I set (with a pot on the base of transistor) As the battery charge goes down. Yes I realize this will flatten the battery faster... Sorry for bumping an old thread. Been googling for a couple of hours and all I can find are photo-sensitive switches, not dimmers.