I googled "bicycle lighting laws Tennessee" and got a link to the actual "bicycle law handbook" Regarding lighting it states;
Every bicycle when used at night must be equipped with a front white headlight visible at a distance of 500 feet, and a red rear reflector visible at a distance of 50 feet.
The 500ft distance is not the distance you should be able to see the light but the distance that if you are coming from in front of you that the light can be seen by others. Like a weak flashlight in the dark, you can't see far with it but people can see it from a long ways away.
You can look here for the rules in your state.
http://www.freewebs.com/92jeepwrangler/state%20bike%20laws.htm