When entering the herp-keeping hobby it soon becomes apparent that there are several approaches to providing heat for our animals. It can all be overwhelming especially as standards continue to improve over time. Here we will go over the what, why, and how of heating for reptiles to better explain the best ways available to keep your animals heated in the ways closest to nature. Much of this information has come from the expertise provided by Dr. Frances Baines and Roman Muryn, who have advanced the field of reptile husbandry through their dedicated time researching different lighting and heating methods. They provide much of their findings and advice in the Facebook group Reptile Lighting – I would highly recommend joining and benefitting from the files and discussions there.

What is heat to a reptile?

Reptiles are ectothermic. This means they cannot regulate their body temperature internally. Consequently, they must use the environment around them to warm up and cool down. This is ultimately what determines the natural distribution of reptiles (and amphibians), and why their diversity is at its height around the equatorial tropics.

All physiological processes in their bodies depend on this temperature regulation, stemming from rates of oxygen consumption. The hypothalamus in the brain acts as the internal ‘thermostat’ that prompts reptiles to seek warmer or cooler areas to regulate their temperature back to their natural “set-point”. They are more active when sufficiently warm, which means more opportunities to eat, fight or reproduce. Water loss also ties in closely with temperature regulation, especially in amphibians. Changes in temperature stimulate behaviours such as hibernation, followed by reproductive cues when the temperatures rise after this period. Temperature is also critical for incubation and in some cases even the sex determination of offspring.

Other significant reasons for reptiles basking in heat include: circadian rhythm maintenance, managing viral infections or parasites, healing wounds, drying and shedding.

To maintain our reptiles and amphibians to the highest quality we can, it’s important that we give them as close to the complete spectrum of light and heat as possible, presenting the options for their own regulation within an enclosure. To see what we need to offer, we look to nature’s heat lamp: the sun.

The Lamp in the Sky

In the world of reptiles, the sun provides all heat and light radiation needed for their physiological activity. Estimations vary, but around 50% of the sun’s radiation is infra-red, ~40% is visible light, and the remaining percent is UV rays. We already know it is important to provide a source of UVA and UVB light which are essential for vitamin D3 production, among other processes. UVC is blocked out by the ozone layer.

The radiation that provides heat – infrared – is also grouped in three ways, depending on the penetrative quality. They are named far-infrared (IRC), mid-infrared (IRB) and near-infrared (IRA). Think of standing in direct sunlight on a summer’s day compared to standing near a radiator on a winter’s night and how those heat sources feel different on your skin.

This graph is based on work done by NASA – it can be presented in many formats. This one features attenuation dips that represent energy absorption by water and carbon dioxide. This allows a good visual for separating the various groups of wavelengths.

Heat and Reptile Physiology

As we have mentioned, an appropriate heat source is an essential factor of life for herpetofauna as they are ectotherms that must rely on external conditions to regulate their body temperature. Most know this related directly to general activity levels and digestion of food, but it’s more complex than that. All physiological processes that occur within their bodies are temperature dependent, and this includes biological mechanisms that relate to disease resistance.

Many reptiles are also temperature-dependent in the embryonic stage. TDSD, temperature-dependent sex determination, is known among all crocodylians, some turtles and many lizard species. Generally, warmer temperatures will yield more males and cooler temperatures yield more females, while in some cases a median range will produce a mix. New studies have observed genetically determined species to be influenced by extreme incubation temperature changes.

Seasonality of temperature influences the reproductive cycles of reptiles and amphibians as well. It is common for a cooler period to result in a semi-hibernation known as ‘brumation’. After this, when the weather becomes warmer again, signals the breeding season of many species. Captive keepers who breed reptiles can artificially simulate this temperature seasonality to spur on reproductive activity in their animals, and allowing brumation is often considered beneficial for the long-term health of reptiles that do it as a natural part of their life history – such as tortoises.

So, temperature directly affects herps even before they are born, and influences their activity level, performance, and therefore ‘fitness’ and biological success in the wild.

The habits encompassing thermoregulation differ between species, due to differing environments and weather patterns. A commonly observed pattern is for reptiles to bask in the early part of the day, until they are sufficiently warm enough to perform other daily activities, and in some environments, avoid weather extremes such as temperatures exceeding their tolerable maximum or heavy rainfall.

Reptiles are also described as “heliothermic” – getting their necessary body heat from the sun. The behaviour of basking to the optimal temperature and then retreating to shaded areas throughout the day is known as “shuttling heliothermy”.

What’s more, the concept of ‘belly heat’ that has circulated the hobby for years is pretty much debunked when you look at the natural heat source – overhead, from the sun.
This concept was in relation to the need of heat for digestion and the use of heat mats and sometimes hot rocks (hot rocks are not recommended as they easily cause surface burns, unable to be controlled by thermostats).

It’s understandable to want to apply IRC given off of surfaces to this idea, and it can’t be argued that reptiles were indeed kept for a long time often with no other heat source than an IRC-emitting heat mat.

The problem is the lack of efficiency, as we know from the penetrating ability of each infra red wavelength type. For proper heating of the internal tissues and organs, IRA would do the best job. Your reptile should not have to be soaking up the heat source constantly in order to digest, as they would likely have to when only supplied with an IRC source from below.

Coming back to the infrared categories, we mainly need to understand how they affect our animals directly. Shorter wavelengths have higher energy, and the reverse is true for longer wavelengths. IRC is long-wavelength heat that in nature is usually found re-radiated from objects heated by the sun in the day, like rocks or road surfaces. We often call this “background” or “ambient” heat. They warm the air slightly, but you would have to touch it to feel the warmth, and it would only heat the outer layers of your skin. You can use this effect in your own enclosures by using flat rocks or slate that will absorb IRA and re-emit it in the evening for a while as IRC. Other heater types as we will cover later emit solely or the grand majority IRC, and are used as ‘supplementary’ or ‘ambient’ heating. IRC from the sun doesn’t actually reach the earth directly, it is re-emitted from surfaces such as rocks that have absorbed IRA.

IRB has slightly better penetration (~1-2mm) but does not reach the deepest tissues and blood vessels.

IRA is considered the best for thorough heating, as it penetrates up to 10mm into the body, effectively warming deeper tissues and blood vessels. It means that a reptile basking under IRA will be warmed more thoroughly and more quickly – as they would under strong sunlight. They don’t have all day to wait around to get warm in the wild!

So, what heating equipment should we use? The aim is to provide as full a spectrum of light and heat wavelengths as we can. Ideally, we simulate the full range to give our animals the choice of exposures as they regulate throughout the day and night. For animals that bask, it is especially important that a source is provided that will efficiently and evenly warm them up as the sun would every morning in the wild. This, in conjunction with UVB exposure, is an essential part of our animals’ daily routines and overall health.

Incandescent Lamps

These lamps, especially tungsten-halogen lamps, are currently regarded as very good choices for basking spot apparatus. They produce a lot of visible light, but IRA is also produced as heat (more so in the tungsten and halogen lamps mentioned because of the filament used). In the case of keeping reptiles, it is good for lights to be ‘inefficient’ since they produce more heat as ‘waste’ energy. A good proportion of this heat is deep-absorbing IRA, followed by some IRB and C as well. Because of the bright light and IRA heat, they make a good basking spot for mimicking the sun for reptiles. They also complement the use of UVB tubes very well, as they provide red-yellow light, while UVB tubes provide blue, giving a ‘full spectrum’ of visible light when paired together at the hot end/basking site.

Metal Halide Lamps

Metal halide lamps are a popular choice for basking reptiles but have some caveats to consider. They are not compatible with thermostats and therefore should only be used in vivaria large enough to prevent overheating. Most do not produce any UV, although some that do are in development. They are extremely bright and require an external ballast and need to be positioned at a safe distance. Used correctly they can be very good for daylight basking reptiles, paired with the right UVB lighting as well.

Mercury Vapour Lamps

These also reach high temperatures due to incompatibility with thermostats, so they should only be used in large enclosures following manufacturers’ instructions for placement. The appeal of these lamps is that some produce UVB, which puts together lighting and heating in one convenient lamp. A flood lamp style that creates a wide spread underneath is best for even exposure onto the animal below. This creates an artificial ‘sunspot’. If using these for UVB, make sure they produce enough for your species.

Infrared Projectors

Also a fairly new innovation, these produce heat with barely any light at all. It is mostly IRB and C, with a small amount of IRA, making them the popular choice for evening or supplementary heating alongside a primary light source. IRB and C re-radiated from the substrate and surrounding objects creates a nice warm ambient temperature. Alone, they would not expose a species heavily reliant on daytime basking (such as a bearded dragon) to quite enough IRA for thorough warming through the whole body.

Ceramic Heat Emitters

Another lightless heat source, CHEs are a popular choice for secondary heating, especially for ambient warmth at night. A common misconception is that they are suitable as a heat source alone, but they only produce IRC and some B at best. The ideal way to use these lamps is as overhead long-wave heat, especially where the substrate is deep and prevents the use of a heat mat. If you have a particularly large enclosure, CHEs can help to extend and maintain the thermogradient. Low power ceramics are great for overnight heating if your house is too cold for your animal. Be aware that they need their own ceramic fitting installed and a guard if your animal can reach the lamp in any way.

Heat Mats, Cables, and Radiant Heat Panels

Heat mats and cables emit almost solely IRC. They will warm the skin of reptiles in close contact and the air very slightly but do not produce the full spectrum of infrared radiation needed for thorough heating. With the widespread acceptance of deep loose substrates increasing, heat mats are becoming less useful as more than an inch of a substrate on top presents a risk of overheating the mat and blocking the heat produced from reaching the animal properly. Heat mats and cables can be used as supplementary heating, so long as they are not obstructed. Quarantine housing for animals that cannot be on a loose substrate can utilise heat mats/cables effectively. They can also be stuck onto the side of glass tanks for some ambient warmth if fittings for ceramic lamps are not feasible.

Coloured Heat Lamps

Red, green, and blue or purple bulbs are common in the exotic pet market. However, there aren’t any beneficial reasons to use these and they may even be harmful long-term.

It used to be said that reptiles could not see into the red spectrum, especially if they were nocturnal. However, while some nocturnal reptiles do lack red-sensitive cones in their eye structure, their green-sensitive cone does respond to the light source – meaning they are aware they are not in darkness. Night lamps such as ‘moonlight bulbs’ are in reality much brighter than the light provided by the moon, so they are definitely detectable at night. The main consequence of this is the interruption of your animal’s circadian rhythm. Even if they are nocturnal, it can be disturbing and detract from their natural behaviours. The closest simulation of natural moonlight was achieved by placing a single LED in a ping pong ball.

In terms of heat, these bulbs generally put out infrared warmth in varying ratios, so they will contribute to ambient heat. An appropriate way to use them would be in conjunction with white lights to dilute the intensity of the colour, adding a small desired aesthetic effect without obscuring reptile vision to a huge degree. This is usually done to achieve an effect such as “green rainforest light”, but again we emphasise that this isn’t in any way necessary or beneficial and so the animal’s welfare should not be disregarded for aesthetic pursuits.

Thermostats are essential – here’s how to pick the right kind for your heat source

When keeping exotic pets warm with a heat source it is imperative to use a thermostat. This safely regulates the temperature in the appropriate range for your animal and prevents the risks of overheating, which can even cause fires. As there are different kinds of heating sources, there are also different kinds of thermostats. Each will be better suited to different heat sources. We will go over these here in order to explain the best uses for each.

On/Off Thermostats

These are the most basic and usually cheapest kind of thermostat. As the name suggests, they turn the heat source on or off depending on the temperature reading of the probe. Because this causes the heat source to repeatedly cool down and heat up to meet the set temperature, it maintains a range of temperatures around the one that has been set. This can be problematic if you don’t want too much of a temperature fluctuation.

This type of thermostat is not suitable for any light emitting heat sources. The light would be repeatedly turning on and off, interrupting the enclosure’s photoperiod as well as causing the bulb filament to blow very quickly. On/off thermostats are most commonly used for heat mats and heat cables. The temperature probe should be very close to or in contact with the surfaces of these heat sources to properly control the temperature the animal will be in contact with.

Pulse Thermostats

Often called pulse proportional thermostats, these are also best suited for non-light emitting heat sources and are more commonly used for ceramic heat lamps. They work by monitoring the temperature at the probe in comparison to the set temperature and adjusting the intensity of the electrical pulses sent to the heat source to power it accordingly. This action would not be suitable for light sources because it would wear them out faster as well as being visibly perceivable to the animal in the enclosure. The probe should be positioned at the main warm spot in a direct line from the source, or on the cool side if you are using the heat source for ambient warmth, to ensure . The increase or decrease in electrical pulses as the temperature reaches the set point creates a reliable and stable temperature.

Dimming Thermostats

This is the type of thermostat best suited for light sources – but are generally suitable for most others as well. They are the most accurate kind of thermostat, as well as the most expensive. Dimming thermostats work by adjusting the amount of electricity provided to dim or brighten the light output, which alters the heat output at the same time. If the heat source is lightless then it just alters the flow of electricity to the heat source. The dimming and brightening is extremely subtle and does not cause disturbance. It is also very well controlled and accurate. You still need to purchase a light with the correct wattage for the temperature output you want or the thermostat will overly dim/brighten it to meet the set temperature.

Quick Guide

• On/Off Thermostat: lightless sources, usually heat mats and cables
• Pulse Thermostat: lightless sources
• Dimmer Thermostat: most heat sources; ideal for light emitting heat sources

Other considerations

Whatever thermostat you end up choosing, the wattage of the heat source you are choosing should still appropriately match the temperature you are looking to achieve. Often the packaging will have guides for this. You should also make sure that the wattage of the thermostat is not exceeded by that of the heat source you are connecting it to. This also goes for thermostats that can control multiple apparatus.

Temperature probe placement needs to give a good reading for the area you are trying to control. For basking hot spots, place the probe directly in line of the heat source, where the animal will be exposed. To monitor ambient temperature, placing the temperature on the cool end of the enclosure can help to ensure that the temperatures do not get too high and a cool refuge is maintained. Thermostats should be used in conjunction with accurate thermometers in your enclosure, as well as a hygrometer if appropriate.

Thermostats can usually be connected to multiple heat sources at once, which is useful if you are housing multiple individuals of the same species under the same conditions. Some more advanced thermostats are now on the market, including touch screen models that are programmable with day/night temperature changes, alarms when an extreme has been exceeded, and timers for heat sources.