While reptiles come in all shapes and sizes, all require some mixture of appropriate temperature, ideal humidity, and exposure to the day/night cycle to live and thrive. Yes, even reptiles and amphibians that have developed in closed cave systems where the sun never shines still rely on the sun and moon—as well as their effects on seasons, air pressure, and tides—alongside the right temperature and humidity. In captive conditions, these are the three primary factors that require constant management from keepers as well.
However, it’s not necessarily a simple matter to measure temperature, humidity, and UV exposure in an enclosure. In fact, it’s common for keepers (and especially new hobbyists) to report that one temperature or humidity gauge is giving them wildly different information than another placed in the same habitat. What are you supposed to do in this situation?
To promote healthy, happy animals, it’s the keeper’s responsibility to understand how to accurately measure the many metrics inside an enclosure. Let’s take a look at the best ways to achieve the most accurate results.
Measuring Temperatures: Basking and Ambient
Because reptiles (and other exotics, like amphibians) are cold-blooded, they regulate their body temperatures using their environment. In a captive environment, this usually looks like an animal taking time to bask on a dedicated basking platform or going to the cool side of an enclosure if they become too warm. But how do you know that the basking spot is the right temperature—not too hot to burn your animal, but warm enough to support their digestion?
Many hobbyists will install a temperature gauge next to the basking spot, but this doesn’t paint an entirely accurate picture. There are two elements that make up an enclosure’s heat: ambient temperature and surface temperature.
Ambient temperature describes how warm or cool the air is. Electronic thermometers are typically the most accurate at measuring ambient temps because they can take precise readings at high speed. A digital thermometer will do this by measuring how easily an electrical current flows through the metal inside the thermometer; at higher temperatures, the flow experiences less resistance. This makes digital thermometers much more accurate than dial gauges, which are commonly sold in pet stores as simple “stick and use” solutions.
The basking (or surface) temperature in an enclosure is a reflection of how hot that specific material is to the touch. Because heat radiating from surfaces contributes to ambient temps, the basking temp is almost always hotter than ambient—which means if you’re using a nearby thermometer to measure the basking spot, your number is probably not accurate.
Instead, the most accurate method of measuring the basking spot is using an infrared (IR) thermometer. These devices are often simply referred to as “temp guns” or laser guns because they are hand-held devices that shoot a laser beam, which makes them look similar to a gun. This laser detects the radiation coming from a surface and converts it into a temperature reading, which is displayed on a screen on the device. Just be sure that the laser is reaching the desired object! Shining the laser through an enclosure door onto the basking spot will be reading the temperature of the door—the first solid object that the laser is interacting with—not the basking spot.
Measuring Humidity: Water Vapor and Saturation
Humidity is a description of how much water vapor is in the air. The higher the humidity, the more water droplets the air is holding—and the less space it has for more. When the humidity reaches 100%, the air cannot hold any more moisture; this is called the dew point.
Some reptiles need a lot of moisture to keep their skin and mucous membranes saturated. Others thrive in drier conditions. No matter which species you keep, you’ll need to have an accurate reading of how moist the enclosure is, and the best way to do this is using a digital hygrometer.
Hygrometers work by interpreting changes in material conductivity and weight as they interact with moisture. A digital hygrometer can do this instantly, which means that just like with temperatures, keepers should avoid using analog dials or gauges because they are known to be less accurate.
Additionally, the placement of the hygrometer matters. Heat rises, which also means that higher locations tend to be drier than lower ones. In an enclosure, the area immediately above the substrate is likely to be the most humid (aside from within the substrate itself). For the most accurate reading of average ambient humidity, place the hygrometer part-way up the side of the enclosure. It is often helpful to use more than one hygrometer—one for average humidity and another for targeted humidity, such as inside a humid hide.
Measuring Ultraviolet Light: Angle and Concentration
Most reptiles benefit from ultraviolet (UV) light, which comes from the sun. In captivity, hobbyists mimic this exposure using specialized bulbs that produce UVB radiation. However, one of the biggest challenges with this approach is that UV lights often continue to work (that is, put out visible light) long after they have stopped producing UVB radiation. Thus, many keepers don’t realize that their UV strip isn’t working and that their pet isn’t getting the exposure they need.
In general, it’s recommended to replace UV lights every six months to one year, even if they are still visually producing illumination. However, hobbyists who want to maximize how long they can use their UV strips can invest in a solarimeter (or pyranometer)—the gold standard in measuring radiation.
A pyranometer will tell you how much radiation is being produced by a lamp and at what distance. Radiation is typically strongest right next to the lamp and then tapers gradually the further the reading is taken from the UV source. This is an important consideration for reptiles, as placing their UV lamp too close to them can expose them to too high a concentration of radiation. Most reptiles thrive between 12 to 18 inches away from their UV light.
Another consideration when measuring UVB and placing lights is the angle. UV rays are strongest when they hit their target at an angle between 45 and 90 degrees; this is why humans are most likely to get sunburnt from 10am to 2pm, when the sun is slightly off-peak or directly above them (that is, at a 90-degree angle). Placing a UV light outside of this range, such as suspended on the side of an enclosure, can dramatically reduce your animal’s ability to absorb and benefit from UV rays. In addition, the intense light at eye level can harm their eyes over time. Stick to using UV lamps at the top of an enclosure—and remember that any mesh screens will impact how much UV radiation is penetrating through!