Step up and get your own "dynamo hum"...(FZ). All jokes aside, its a simple dynamo light mounted to a Planet Bike light bracket. On about 6 cranks I get 20 to 25 minutes of light.
There is a 3.6 volt NiMH rechargeable battery that comes in the light. SO, by free I refer to your out of pocket cost on batteries.
Step 1: material
1. dynamo light....Harbor Freight, 2 for $8.
2. quick release light strap...most have a screw to change the mounting base, this is a Planet Bike
3. super glue
4. fingernail polish remover........or acetone