Given the natural desert habitat of the Horsfield tortoise, sunlight, and specifically the components of sunlight are crucial to giving your tortoise a long, happy and healthy life. However, with so much choice in the market, along with the make-up of heat and light lamps, it can be confusing to understand what is required. This article is for use in an indoor enclosure.
Understand the Horsfield Requirements
Using our Ferguson Zone calculator, we know a Horsfield Tortoise is in Zone 3, Partial or Open Sun Baskers, and require a UVI range between 1.0 – 2.6 over most of the enclosure, and between 2.9 – 7.4 in the basking zone.
From their natural habitat, their basking area needs to be between 32-25 degrees celsius, and the enclosure as a whole needs to be a minimum of 17 degrees celsius.
Choosing bulbs can be quite complicated and without a solar meter to measure UVI ranges in your home, you must always use the recommended set up specific to each brand and bulb. The reason being, is that the major companies like ZooMed and Arcadia, record the UVI range at varying height distances so we know where it needs to be placed - without following their instructions, your tortoise may not be getting the right UV due to incorrect height.
The diagram below from Arcadia shows the possibilities. As you can see, T8 and T5’s are both acceptable. Note that:
You can use a 12% bulb in either a T8 or T5 size, but the T5 needs to be further away because it's a lot more efficient.
Alternatively, you can use a weaker percentage 6% T5 Forest bulb, and this is effectively equivalent to a 12% T8 Desert bulb so they can be used at the same height.
How to measure UV Height
When setting up the light in your enclosure, there are a few things to consider.
The light must always be facing directly down (like the sun) to not damage your tortoises eyes.
The bulb used must offer a large enough UV area at the correct height to cover the entirety of the tortoise. In practise, this means using a tube light, or a bulb from a reputable supplier. Alternatively, you can use multiple lights in a similar area, but I'd only recommend doing then when you have access to a solar meter to check the overall UV exposure in that area as it may end up being too high. A blog post is coming soon to show what this looks like.
Height must be measured from the top of the shell, if not, the body of the tortoise may be the correct temperature, but the shell may be overexposed.
The basking area must be raised up to the light, so the tortoise can self-regulate and essentially move down the hill.
On top of UV, Horsfields also require heat, and a simple heat lamp is sufficient for this. When purchasing a heat lamp, also purchase thermometers so you can find the correct height for the temperature required - the lower the bulb, the hotter the area and vice versa. There is no set height for heat lamps as it depends on how warm your house is so it needs to be done manually by you.
Example Light & Heat Set Up