Confused about lights and temperatures

[Mykilleon]

Hi! I'm setting up an enclosure (don't have the lizard yet) but I'm having trouble getting the temperatures just right. This will be a long post but I want to include anything that may be applicable so please read carefully.

I have a slate basking platform that is 13" from the basking light. I am using a Klein dual-sensor infrared and probe thermometer. The IR sensor reads 107°F in the hottest spot, as pictured. But, if I lay the probe in the same spot and wait a few minutes for it to stop updating, it only reads about 80.

I have another digital probe which I've placed about 6" from the center of the basking spot (you can see it in the bottom of the picture where I'm using the probe end of the Klein gun) and it reads 78, seemingly confirming an air temperature of about 80° around the basking spot, which seems really cold given the surface temp.

If I place the digital probe right in the center of the basking spot, it gets to about 103° but only after being left for about an hour. The 96.8 reading pictured was after about 20-30 minutes of being sat there.

I am using a Philips 72W halogen flood light, but it's on a dimmer and turned down about halfway. If I turn it up closer to full power I can get the air temps to 90-95°, but then the IR thermometer reads 120-130° in the center of the basking spot! It's cooler (about 100-110°) as I move away from the very center, but the hottest spot is way hotter than the recommended temperatures. When I put the black digital probe right in the center of the beam with the light at higher power, it also gets up to about 120° after an hour or so.

There is an LED light on the other side of the enclosure for plants. The UVB tube is not turned on as I'm expecting it won't affect the heat much. The room is about 70°F right now. The top of the enclosure is a wide mesh (pictured) so I know a lot of heat is lost that way.

Why is my basking spot so much hotter than the air around it? Is it actually okay for it to be >120° in the hottest spot since it's just soaking up and holding this heat, and it's significantly cooler just a few inches away? Or, should I leave the bulb on the lower setting and cover parts of the mesh top to hold in more heat? Should I use an entirely different kind of bulb? Should I add a CHE and leave the bulb on its lower power?

Thanks so much for taking the time to read this, please let me know what you think!

 

[xp29]

I think you kindda nailed the issue in your post. The slate is absorbing and holding the heat. Maybe try testing your temps with a different type of media under the basking buld. The probes are going to give you the best idea of the actual temperature ofvthe light.
Your also correct about the uvb, it isn't going to add much ambient temp.
Some of the resin hides like from petsmart or a piece of driftwood for the basking might help you get the temps where you want them. Just remember every species of evergreen are toxic to reptiles, especially cedar.

 

[Mykilleon]

Thanks! I always thought you wanted something like slate so their belly gets warmed up, but doesn't keep heating from underneath like a heating pad.

I'll try removing the slate and see if things work out better. I need to let the bioactive stuff get settled for at least a few weeks, so I have plenty of time to find something that works!

 

[Axil]

It looks like your light (and thus the heat) is hitting a very concentrated area. In some of your pictures I see a noticeable bright area right under the dome.

Are you using a par38? I use a Phillips 100w halogen heat bulb which is a par38 and while it doesn't cast an angle as wide as I'd like it to, it doesn't create a light halo like yours seems to either. *edit* the light I linked cast in a 55 degree angle for reference.

Just a thought if changing the basking material doesn't work. Also make sure you leave the door shut when taking probe temps. My enclosure drops 10 degrees the moment I open the glass door.

 

[Mykilleon]

I removed the slate; the surface underneath is insulation foam, painted with Drylok and then brushed with thin layers of acrylic paint.

ThIs did not seem to solve my problem. The digital probes were still getting up above 120° in the center of the beam.

I tried angling the light and turning it up near full power (picture attached, the bricks are temporary, I'll anchor it more stably). The probe in the beam currently reads 109.5 and the one on the log on the right reads 88.1. I've had everything in this position for about 30 minutes now and the temperatures seem to be staying right around there. The Klein IR gun is definitely less accurate on the painted Drylok, as it's showing over 140° in the spot where the probe is, yet I can hold my hand on the surface without a problem.

I think I might still try covering at least a part of the top mesh to raise ambient heat. I may also experiment with steeper light angles or raising it up an inch or so.

Any other thoughts or comments that might be useful?

 

[xp29]

Wider domes also help spread the heat out a little more evenly.

 

[Mykilleon]

FYI this is the exact light bulb I'm using. Philips 429373 Halogen PAR38 90 Watt Equivalent Dimmable Flood

The dome is 8.5".

 

[Axil]

FYI this is the exact light bulb I'm using. Philips 429373 Halogen PAR38 90 Watt Equivalent Dimmable Flood

The dome is 8.5".

Unfortunately the beam angle isn't disclosed on that light (that I can see) so it's hard to say how much the light is focusing it's heat. I've seen floods as narrow as 25 degrees, most don't disclose.

Since the reflector is built into the light I don't think the dome itself can do much to spread it out anymore. Covering part of your enclosure top to keep the heat in is probably going to help get your warm side correctly heated.

You still may need to raise the light or find a different bulb if a small area is getting most of your heat. The dragon should be able to get at least his head in body into the basking temp zone.

 

[Mykilleon]

I googled it and looks like it's about a 25° beam angle a wider-angled light would probably really help, I'll try that.

 

[Axil]

Ok, according to response to a question on this bulb on the home depot site, Phillips says your bulb has a 25d beam. If your fixture is deep enough you may be able to use a halogen with the traditional bulb shape (A22 style I believe) that would spread out the heat a lot.

Alternatively the bulb I linked earlier is the same shape as yours but has more than twice the dispersal

 

[Mykilleon]

The dome is actually pretty shallow, so much so that the bulb I'm using actually touches the mesh when it's not raised into anything. I think the bulb you linked might be exactly what I need!

 

[Axil]

I googled it and looks like it's about a 25° beam angle a wider-angled light would probably really help, I'll try that.

Beat me to it!

It aggravates me they consider that a flood.

 

[Axil]

The dome is actually pretty shallow, so much so that the bulb I'm using actually touches the mesh when it's not raised into anything. I think the bulb you linked might be exactly what I need!

Sounds like the same dimensions as my 8.5 dome. A par38 sticks out like half an inch.

It aggravated me so much I just bought a deeper one today so I don't have to worry about bumping it and throwing my temps five degrees off.

 

[Claudiusx]

The Klein IR gun is definitely less accurate on the painted Drylok, as it's showing over 140° in the spot where the probe is, yet I can hold my hand on the surface without a problem.

Your IR gun is most likely plenty accurate, but you're using it wrong, and this is the issue with IR guns and why I don't recommend them.

Your probe thermometers are giving you the true temperature. Any adjustments you make need to be based off of your probes, not your IR gun.

The issue with IR guns is they measure temperature by measuring light coming off an an object in the IR spectrum, and this gets measured in the device and converted to a temperature. The issue is different materials absorb and reflect IR spectra differently. This metric is called Emissivity, or E-value for short.

Most IR guns come pre programed to measure surface temperatures of objects that fall into an E-value around .95. This is pretty good for a majority of items. But for some items, this falls way out of the range of what is needed to accurately measure temperature.

For instance, Slate has an E-value of 0.67 - 0.80. This is WAY outside of the range of the average IR gun, which means your IR gun is not going to give you an accurate temperature. It is also why you can hold your hand on a surface that is reading 140 degrees. It's because the surface is not actually 140 degrees, your IR gun is only assuming it is based on the assumption that it's E-value is .95, which it clearly is not.

Digital thermometers with probe ends do not have this issue. Place your probe on the spot you want to measure and let it sit for 10 minutes or so. That is going to be your accurate surface temp. Probes don't only measure air temp. They end up measuring surface temp too once set in place long enough (10 minutes) as the probe will heat up to equilibrium with the surface it is resting on.

IR guns can still be used, but they need to be confirmed first by using a probe. If the two measurements agree, you can assume your IR gun is reading the surface temp right. If they don't, the surfaces E-value falls outside of the range of your IR gun.

You also can buy IR guns with adjustable E-value settings, you just need to know what the E-value of your material is.

-Brandon

 

[Mykilleon]

Probes don't only measure air temp. They end up measuring surface temp too once set in place long enough (10 minutes) as the probe will heat up to equilibrium with the surface it is resting on.

TYSM for your response! I knew some of that about the emissivity but that's by far the most thorough explanation I've gotten for it.

One more question about the bit I quoted above, just because I want to be absolutely clear. The actual probes of my thermometers are like inside of a little plastic cage (you can see what I mean in the pictures on the original post). I'm worried that this affects the temperature as they sit under the light and the plastic heats up. Is this something I should be worried about? If I leave it under the light too long, will it start to be inaccurate?