I’m a bit late to the show on this one but this was my solution to a similar problem:
http://www.instructables.com/id/Throwduino-Basic-Light-Sensing-Flashing-Throwie-/
It’s a throwie consisting only of an LED, an ATTiny85 and a CR2032. The trick is that the LED can also act as a photodiode and the ATTiny has an analogue voltage sensor so you can read the ambient light level without any additional parts.
Message me on instructables (or here if the facility exists – looks like it might) if you want a hand with code that could fade up & down as you were looking for.
Ugi
