Temperature help!

[Stevievee]

Firstly apologies for all the questions, this will ease off as I become more confident...
My question is about heat and basking! I have a 100w spot with separate UV. I have a probe at shell height that never seems to get above 25c. The lamp is about 30cm above the substrate. As the day goes on the heat intensifies. Substrate getting upto 35c, with surrounding substrate temps being up to 32c. Probe still saying 25c. I checked it this morning with a temp gun after the light had been on an hour and the substrate temp was 25c. The substrate is never hot to touch, just warm! I am having to wake Titus in a morning and I'm wondering if I'm doing something wrong? This temperature thing just isn't sinking in for some reason. Should the probe say 30c, thus ground level getting pretty hot, especially over time as the day goes on. The heat beating down on one spot for a number of hours would do this surely??? He has been under the lamp now for 20 minutes, but still feels cool to the touch! Help!!!!

[Nina]

No apologies necessary, and keep those questions coming! This is a really interesting -- and difficult -- question, and something we all struggle with. There are two temperatures, as you've discovered -- the air temperature and the surface (substrate) temperaturre). I tend to measure the air temperature and neglect measuring the surface temperature, which is neglectful of me, because they are both important -- and they can differ widely, because the substrate absorbs the radiated heat from the bulb and becomes much hotter than the surrounding air. In the same ways a tortoise''s shell is also very good at absorbing the heat from you bulb. I just found a good (if long) explanation of this on The Tortoise Forum, from someone called 'Turtlesteve' (lol, any relation?) in 2020: Here is what he says (please note that an 'IR thermometer' is the same as a 'temp gun'.

______________________________________________________________
When measuring temperature in a tortoise enclosure, there are two temperatures that you can measure:
- The AIR temperature in the enclosure
- The SURFACE temperature in the enclosure

Both of these are important.

In an enclosed place without light, such as inside a hide box, these temperatures will be almost the same. Everywhere else they will be quite different.
So first of all, why do they both matter and what should they be? We want to make sure the tortoises are not overheated or chilled, especially for hatchlings. So when the tortoise is hiding in a hide box, or somewhere in a dark corner of the enclosure, the body temperature of the tortoise will gradually reach the air temperature. But when the tortoise is out and basking, they will rapidly heat up, by absorbing radiation. This is where the surface temperature matters. So, the minimum air temperature should be kept high enough to prevent the tortoise being chilled, and the maximum surface temperature should be some reasonable value to avoid overheating. I prefer much lower temperature gradients than are often recommended. For tropical tortoises I tend to aim for 80-85F air temperature and 95F surface temperature in the basking area. For hatchlings I will narrow the range even more. Nighttime air temps can drop (and I think this is beneficial). I like 75-80 for tropical species and 70-75 for temperate species. I feel like most of the time, tortoises are being kept under EXTREME temperature gradients that are not beneficial. Part of the problem is that temperatures are not being measured right. The rest comes from people (in the past) pushing extremely powerful basking bulbs and open/ventilated enclosures...

So now with regards to how this is measured:

AIR TEMPERATURE: Should be measured with a probe thermometer in a shaded area (indirect light only). It is not possible to measure air temperature with an IR thermometer but you can estimate it as noted below. Other thermometer types are acceptable (liquid thermometers etc.). If the thermometer is directly exposed to the basking light it will read wrong.

SURFACE TEMPERATURE: Should only be measured with an IR thermometer. However, you will often NOT get a useful reading by pointing the thermometer at some random surface. The surface temperature depends on the surface! IR thermometers will generally give bad readings on white or highly reflective surfaces. The proper way to make this measurement is:

- Find a "standard" surface. Generally you want to make sample coupons that are matte black in color and 2-3" in size. I use cardboard packaging inserts (that were dyed black) and cut them into squares.
- Any time you want to measure IR temperatures, put these sample coupons in the enclosure where you want to measure temperatures. In this case you want the coupon to be exposed to the basking light as the tortoise would be. Let them reach equilibrium.
- Use the IR gun to measure each surface sample and use this as your surface temperature measurement.
- Tortoise shells are very good at absorbing IR and will heat up much more than the surrounding substrate. This method is a better estimate of how hot a tortoise will get than pointing the IR gun at the substrate.

If you only have one thermometer, it should be an IR type. But it is very helpful to have a non-IR thermometer for measuring air temperature. You can estimate the air temperature by hanging a sample coupon in the air, in a shaded area, and measuring it with the IR thermometer.
________________________________________________________________________
-
Does that help at all? I just measured the temperature of the air and substrate on my two lamps and one is 30C air temp and 37 substrate temp, and the other is 29 air temp and 36 sub temp, and I think that's a bit high, but I'm not going to change the lamps because at the cooler end of the table it's 21C, which is fine. What is important is that your tortoise is able to wander away from the hottest area and into a cooler area in order to thermoregulate, and this is what they do in nature. It's another reason why I like having the separate UVB tube, because when the tortoise is in the cooler area he can still get UV and doesn't have to be under the lamp to get it.

Nina

[Stevievee]

[attachment=0]PXL_20240324_114304851.jpg[/attachment][attachment=1]PXL_20240324_114239997.jpg[/attachment][attachment=2]PXL_20240324_114234201.jpg[/attachment]

Thanks, that's great and your last paragraph has answered my question. I've been worrying about substrate temperature, so not allowing my ambient temperature to get up high enough. So he's been cold bless him. I have made a small white shield so the probe is not in direct light. Titus' shell temp is 30.2c where is is sitting at the moment (in photo). Cooler end a consistent 20ish. I have now lowered the bulb to get ambient air temp of 30c.

I have literally scoured the internet with no luck and you've just explained it perfectly!! Thank you Nina

[jamesthompson]

Some substrates, like wood chips, don't retain heat as well as others. While the substrate might feel warm, the surface temperature directly under the lamp could be much higher.

[Stevievee]

Hi, I have a mix of soil and sand this obviously retains heat well. I was just worried substrate temp at 35c was going to be too high. I now realise that's probably fine, so have started paying attention to probe temperature, trying to keep this a consistent 30c.

Thanks for all the advise, much appreciated.

[Stevievee]

Hi all
Quick question about shell temperature when basking. Titus got up this morning and is currently warming himself up for the day ahead. He has been under his lamp for the past hour and when I've temp gunned his shell it is 32c. I'm assuming he's a little radiator and his shell will heat up to this, even in the correct temperature, retaining the heat from the lamp? He seems quite happy and can move if he wants I suppose! Cooler end still a steady 20c.
He's eating well, not pooing much, roughly every 3 days or so. Wee is fine and urates toothpaste like. Bathing every day at the moment.

He's chilling while I'm killing myself building his outdoor enclosure in the back garden!!

Thanks again for all the help and reassurance.

Steve

[Nina]

Hi Steve,

It sounds like you and Titus have it all sorted -- absolutely perfect conditions, temperature, urates etc. -- he is one lucky tortoise!

Would love to hear/see your plans for the outdoor enclosure. Just make sure that he can't dig under and out of any walls (so sink them in the ground), or climb up and out. A nice little lip facing inwards will prevent escapes, as will ensuring that there is nothing next to the wall (plant, hut for sleeping etc.) that he could use as a ladder to climb out. I've probably posted these to you before, but in case you hadn't seen them, here are some photos of Horsfields defying the laws of gravity and trying to escape.

Nina
[attachment=0]Tortoise climbing wall.jpg[/attachment][attachment=1]Tortoise climbing fence.jpg[/attachment]

[Stevievee]

A work in progress... I post pics once it's complete!