I rarely leave them on more than maybe 3-4 hours, and they really don't get hot at all. I put two per each DETOLF, but if you've got them close together, as I believe you do, you can just put one per, if you're really worried about heat buildup. I think IKEA sells LED style lighting as well in the same sort of configuration, and those put out little to no heat at all. It's worth looking into, as it really makes them look fantastic.