100lux in Pocket
Build a 100~ lux light source which attached to your keychain
Find a Case and Make the Battery Pluggable.
usually garage door remote or cheap mp3 player cases works. find a small piece of conductive metal and glue it as battery connector. don't forget to solder wires to it.
Led Module and Button Placement
i used this one http://www.dx.com/p/2w-9-smd-led-126-lumen-6500k-w... in this sample. using it almost 1.5 years. not bright as first day but still got enough battery to use it in emergency cases.
push-button was salvaged from an old pc case (probably power button) you can use something similar which in same size or purchase together with led module: http://www.dx.com/p/3-pin-push-button-switches-red...
Final Connections
to prevent corrosion, connect the wires and solder them. then glue the led module to back. hot silicon also can protect the led module.
Result
now you got 100 lux light in your pocket.
cost: ~$3
time: 1 hour