Charge/in use light
Typically the charge light will stay on as long as the phone is on the charger. After 16hrs, the battery should be fully charged. Leaving it on the charger constantly can actually overcharge the battery, shorening it's life. The best thing to do is use it until it tells you the battery is getting low, then charge it uninterrupted for about 8-12 hrs. Of course, that's ideal and can't always be done, but the more you can do that, the better.
Hope that helps, and please rate my answer, good OR bad.