How to lower heat on mercury vapor bulb?

Hey guys, this is kind of urgent so I would really appreciate any advice asap. I use the Powersun 160w on both of my girls' 75gal enclosures (48"l, 18"w, 21"h), but at it's hottest point the surface of the basking spot can reach up to 115 degrees. I thought a dimmer would solve my problem, so I got one yesterday... but now I'm reading that you can't dim these kinds of bulbs. Is that true, and if so then why? How do I reduce the temperature without a dimmer? Right now the lamps are sitting right on top of the screen lids of their enclosures.

Also, wanted to add... the temps at the highest point they can get to actually stay between 100-105 degrees, but they have lower level basking spots that they prefer to use most of the time. These consist of a clay turtle shell and a rock cave, which are the surfaces getting up to 115 degrees. I think it's more the materials these things are made of, which absorb more heat than the wooden branch will, that make it too warm as opposed to the actual light or ambient air temperature. Will my dragons get burnt climbing on top of a 115 degree surface, or how much do I need to worry about this? Thanks!

The reason you can't dim a mercury vapor bulb is because they are self ballasted, and they are actually two types of filaments inside one bulb. Put on some sunglasses and look at the bulb when it's on - you'll see both filaments lit up. The incandescent filament can be dimmed, but the one that emits UVB can't.

The basking spot you're describing is actually just fine for the cage sizes you are using. With that much space to escape the heat, the basking spot can get quite toasty without being an issue for the beardie. Consider their behavior; they are selecting the lower down basking areas with hotter surface temperatures over the higher basking areas with lower surface temps - they are telling you they not only are okay with such high temperatures, but they prefer it.

115 won't burn them as long as they are able to escape the heat. Sounds like you have it set up just right.

If you are still concerned with the high temps, the best way to decrease the temps is to get a lamp stand and raise up the light from the top of the cage. Just moving it a few inches above the screen can have a dramatic effect on the high temps within the cage.

-Jen

Thank you so much Jen, all of that makes a lot of sense! I figured if they were too warm then they would just move. However, I am also under the impression that that they don't sense heat from their undersides so I didn't want them to unknowingly burn themselves. I'm not even sure how true that is anyway.

I'll just leave it the way it is for now, but I do think they need another light to brighten up the cool side of their tanks. It already gets up to 80-83 degrees, but it's dim. Do you know what kind of bulb I can use to add light but not heat? Thanks again for all of your help!

XtinaLotusMonster":1kz711e4 said:

Thank you so much Jen, all of that makes a lot of sense! I figured if they were too warm then they would just move. However, I am also under the impression that that they don't sense heat from their undersides so I didn't want them to unknowingly burn themselves. I'm not even sure how true that is anyway.

I'll just leave it the way it is for now, but I do think they need another light to brighten up the cool side of their tanks. It already gets up to 80-83 degrees, but it's dim. Do you know what kind of bulb I can use to add light but not heat? Thanks again for all of your help!

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The issue with the belly heat thing is that it's not that they can't feel heat on their bellies, it's that when provided with a heat source such as a heat rock (which is usually somewhere involved in a conversation saying that beardies or any reptile can't feel heat on their stomach), they'll stay on it to the point of burning themselves. They do so because they need to warm up all the way through their bodies, but can only hug the rock for heat. So, in order to get warm through their entire bodies, they'll ignore being burnt on their stomach to try and warm up their entire body enough to function properly. It's not that they can't feel it, or are too dumb to move - they have to be a certain temperature to function, and will simply sit on or under a heat source until they reach that temperature, and when it's not a suitable heat source burns can happen. This same effect can happen with a small spot light that is too close, as well, but you see it less often.

I would say just pick up a 2.0 UVB bulb or even one of those energy saver bulbs to just put on the cool side. It'll brighten it up without putting out too much UVB (the powersuns put off enough all by themselves).

-Jen

Really useful information, thanks a bunch - I very much appreciate it! It's easy to misunderstand things with all the "unofficial" information out there. I'll try one of those lights