Old Christmas-tree lights need to be disposed of properly because they contain lead--which, if it seeps through cracks in the bulb or is released from a broken bulb, is a health hazard to those who come in contact with it. There are places you can send or take your old lights to dispose of them safely.
Find an old box that can be used for shipping. Place the lights inside. Do not add anything else to the box, such as fabric, plastic bags or old newspaper. Just place the lights into the box by themselves.
Write the name of the company and address to which you will be sending the lights on top of the shipping box. Please visit the resource below for more information on where you can send your lights.
Take the lights to the post office. Make sure that you have placed a return address on the box. Also, make the post office aware of what is inside the box.
Tape an envelope to the box with your e-mail address inside so the company will be able to send you a coupon to help pay for new LED Christmas lights.
Take the lights to your nearest Home Depot.
Drop the lights off at the service desk. They will dispose of them properly.
Ask for the money-off coupon they offer (as of 2009) for new LED lights.