Metro 2033 Light Sensor
I'm working on a Metro 2033 cosplay costume and being the gadget-geek I am I'd like to make a working copy of the light sensor Artyom carries on his wrist. For anyone who haven't played the game (or read the book, I bought it today but I don't know it he's got the same thing there) it's basically just three LED:s (red, yellow, green) that light up depending on how well illuminated you are (red=fully illuminated=people will see you instantly and shoot, yellow=partly illuminated=people will see you unless you take cover, green=as good as invisible unless you give away your position with noise or flashlight).
In the game it's abut the size of a 9v battery but flatter and for simplicity I'd like to keep it like that; I don't fancy carrying around an Arduino or something like that on my wrist.
Here's a picture:
So, my question is: Is it possible to make something like that small and simple enough to be stuck to a wristband?