I keep bearded dragons. A few years ago I ordered new Mercury UV lamps for my bearded ones, but the regular brand I bought was out of stock so I had to settle for what was supposedly an equally reputable brand. I changed 3 bulbs at once and a few days later found that one of my bearded men had vision problems and kept his eyes closed most of the time. I was concerned but didn't plug it into a lightbulb until a second bearded man started having the same issues and then a third a few hours later also showed signs. I immediately removed all 3 bulbs as they were obviously the culprits. My two remaining bearded men who were not given these onions had no symptoms. All three affected bearded men recovered, but the first blind man took longer to return to normal. I have since learned that this problem was almost certainly caused by dangerous ultraviolet radiation, which is used to kill bacteria and viruses and is very harmful to living things and particularly harmful to the eyes. I've also found that reptile UVA and UVB lamps are NOT properly regulated and don't have much consistency even within the same brand. By having this meter that tells me exactly how much UV light different bulbs put out and how far away they are from the bulbs, I know my precious children will never be harmed by another poorly made bulb. Yes, I know this solar panel. A gauge might seem like a big expense, but it will save you and your favorite reptiles from what mine went through and it's worth every penny.