Our light is a 100% UVA light. There are no harmful UVB/UVC rays. These other rays can sometimes cause skin irritation. The whole hand can go into the light. The inside of the light is wrapped in mirrored film so that the rays can be bounced around the whole inside so that the entire product will cure. There is an automatic timer of 2 minutes. The product will not over cure; it doesn’t matter how long your hand may be in the light. Be sure not to under cure. This can happen if there is a heat sensation and the client takes their hand out of the light. Just restart the light and have them put their hand in it one extra time.