Build a 100~ lux light source which attached to your keychain
Step 1: 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.
Step 2: 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...
Step 3: 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.
Step 4: Result
now you got 100 lux light in your pocket.
time: 1 hour