I'm working on a wearable watch light meter for manual photography. I shoot film with cameras that don't have built in exposure meters and it would be nice to have one on my wrist. Doesn't have a display yet but I can use my iPhone to read the value via Adafruit's Bluefruit console. I just got this prototype working about 10 minutes ago :D
Code is here: https://gist.github.com/maxogden/1d9715a448f64513507623090f27c437
Sensor is the TSL2591 breakout from Adafruit. Watch is from https://www.tindie.com/products/deadbeelabs/strapon-purple/
Warning: I'm a software person, not a hardware person :)
I have the Puck's battery holder hot glued to the bottom of the circuit board to act as a pivot point so I can depress the entire watch face to have the puck's momentary button switch engage. It even works one-handed if I have the watch on snugly and flex my wrist upwards.