The big problem with these lights are that the clips break!  The hinges are weak, the spring inside the clip is strong, and when I expanded the clip to attach to our tree branch, they just fell apart.  Artificial trees have thicker branches than live trees, and in order to attach the candle, you have to fully expand the clip, and that's when it breaks.  Seven of the ten candles broke immediately.  Since I purchased these last July, and I know they are now out of stock ( it's Dec 6th.), and I could not get a replacement, my husband came up with a fix; he took clothespins, shortened the length, hot glued the candle to it, and painted it dark green.   I now have useable candle lights for my tree.  Thankfully, I have a smart, resourceful husband!  I do not know if they would be ok with a real tree, but I think that repeated use would result the same way.