Tegu Lighting: Basking Temperature, UVB, and Photoperiod

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Tegu lighting covers two separate jobs. One is heat. The other is ultraviolet exposure.

Argentine black and white tegus (Salvator merianae) are large, active baskers. In the wild they slow into brumation once temperatures drop into the low 70s Fahrenheit. A captive setup has to copy a strong basking spot, a real gradient, and enough UVB across a tall, wide enclosure.

Tegu basking temperature and the heat gradient

The basking surface should reach 95 to 100 degrees Fahrenheit (35 to 38 degrees Celsius). That is the actual spot the tegu lies on. Measure it with a temperature gun or a probe resting on the material, not the air above it.

The warm side ambient air should sit between 85 and 95 degrees Fahrenheit (29 to 35 degrees Celsius). This is away from the direct basking spot itself. It is the general temperature of that half of the enclosure.

The cool side should stay near 75 degrees Fahrenheit (24 degrees Celsius). A hot basking spot, a warm side, and a cool retreat form the gradient. A tegu moves through all three to regulate its own body temperature during the day.

Two veterinary sources agree closely on these numbers. LafeberVet gives the figures above. Chicago Exotics Animal Hospital lists a cool end of 73 degrees, a warm end of 85 degrees, a basking site of 95 to 100 degrees, and a nighttime floor of 72 degrees Fahrenheit.

A zoo lighting reference, the UV-Tool published in the Journal of Zoo and Aquarium Research, lists a basking temperature of 35 to 40 degrees Celsius (95 to 104 degrees Fahrenheit) for this species. The top of that range is for the hottest point of the basking surface only. A tegu should always be able to move off it.

A tegu that cannot reach a true cool zone will struggle after a large meal or in warm weather. One with a weak basking spot cannot digest food properly. It also cannot reach normal activity levels.

Tegu night temps and brumation cues

An active adult tegu should not see a sharp nighttime drop. Nighttime temperatures should hold near 75 degrees Fahrenheit (24 degrees Celsius). That is the same figure as the daytime cool side.

A ceramic heat emitter or a radiant panel usually holds that number overnight. It should run on its own thermostat, such as the Exo Terra Dimming and Pulse Proportional Thermostat. The basking bulb and any visible light shut off once the photoperiod ends.

Captive tegus slow down and retire to their burrows once temperatures fall into the low 70s Fahrenheit, often beginning around mid September in the northern hemisphere. Wild tegus in Florida survive true winter cold the same way, by burrowing underground and going dormant. The UV-Tool lists brumation as part of the species’ natural annual cycle.

A captive tegu kept on a stable schedule year round, without a seasonal drop, usually will not brumate. It stays active and feeding through the winter months instead. That same gradient supports normal tegu behavior patterns all year.

Some keepers let an adult tegu brumate on purpose. They drop temperatures gradually over several weeks with veterinary or mentor guidance.

An unplanned cold snap from a failed heater is not a brumation cue. Treat it as an emergency instead.

Heating a large tegu enclosure evenly

Adult tegus need enclosures measured in many square feet of floor space. That size is exactly what makes even heating hard.

One overhead bulb over a six foot or eight foot enclosure makes a single hot spot. The rest of the cage stays cool and drafty.

Most keepers split the basking heat from the ambient heat. A strong basking bulb or mercury vapor bulb covers the hot end. Radiant heat panels or a ceramic heat emitter run lower and steadier across the rest of the warm side.

Deep substrate matters because tegus dig and often thermoregulate below the surface. Under tank heat mats are a poor primary source for an animal this size.

A strong digger can push one against the glass or scratch it loose. It also does nothing for the air temperature a large lizard actually lives in.

Digestion of a normal tegu diet depends on hitting these temperatures. A tegu that cannot reach full basking heat cannot process a meal well. Placement checks matter as much as wattage.

Use multiple digital thermometers at basking height, warm side floor level, and cool side floor level. A single gauge misses dead zones a large enclosure often has.

Recheck readings after any change to substrate depth, decor, or bulb wattage. All three shift how heat moves through a big enclosure.

Tegu UVB requirements: 5.0 or 10.0

The percentage printed on a UVB tube states the share of the bulb’s total output that is UVB. It does not state how much ultraviolet actually reaches the animal. A large basking lizard like a tegu is best served by thinking in UV Index, or UVI, at the basking spot instead.

The UV-Tool, a peer reviewed guide written by zoo reptile keepers, places the Argentine black and white tegu in Ferguson Zone 3, the open or partial sun basker group. Zone 3 animals live at a UVI of 1.0 to 2.6 through the day, with a maximum of 2.9 to 7.4 at the basking spot. A UVI of roughly 3.0 to 4.0 at basking distance sits inside that zone, and it matches the LafeberVet target for large basking lizards.

The rest of the enclosure should read lower, tapering to near zero in the hides. That gradient lets the tegu choose its own dose. Measure UVI with a handheld UV index meter made for reptile keeping.

Reaching that target reliably calls for a high output T5 tube. A compact bulb or coil bulb rarely reaches it at a useful distance. Tube type and distance from the basking spot decide the delivered UVI far more than the percentage on the box.

A low wattage compact bulb, even a high percentage one, produces far less usable UVB than a full length high output tube. Total output scales with bulb size and design, not the percentage figure alone.

That is why “5.0 or 10.0” has no single universal answer. What matters is the UVI a meter reads at the actual basking surface in a specific enclosure. Getting this right is part of the real cost of owning a tegu that new keepers often underestimate.

UVB tube type and distance for a tegu basking spot

Older T8 tubes have lower output. Even with a reflector, a T8 tube typically only reaches a UVI near 4.0 at about six inches from the bulb. That distance is too close to be practical over a basking platform sized for a large lizard.

A high output T5 tube from a reliable line of UVB lighting performs very differently in a quality aluminum reflector. A 12 to 14 percent UVB T5 tube of this type can reach a UVI of about 4.0 at roughly 18 inches from the basking surface. That suits the taller enclosures and raised basking platforms a full grown tegu needs.

UVB output fades before the visible light dims. A tube that still looks bright can already deliver little ultraviolet. Annual replacement is the standard recommendation for quality brands.

Check a tube monthly with a UV meter where one is available. That habit catches a fading tube before it becomes a hidden gap. A gap like that can sit inside an otherwise correct tegu lighting setup for months unnoticed.

Tegu lighting setup and photoperiod

A tegu benefits from 12 to 14 hours of light each day, including the UVB tube. The UV-Tool lists a 13 hour day and 11 hour night for this species. All bulbs that emit visible light should switch off for a true dark period at night, including the basking bulb.

A basic mechanical or digital timer on the basking and UVB bulbs is the simplest way to hold that schedule. Pairing it with a dedicated thermostat keeps heat and light on separate, independently checked controls.

Natural, unfiltered sunlight is a useful supplement whenever weather and safe outdoor access allow it. Sunlight delivers a full ultraviolet spectrum no bulb fully reproduces.

Glass and most plastics filter out the UVB wavelength. Sunlight only counts toward a tegu’s ultraviolet needs when it reaches the animal directly and unfiltered.

Some keepers shorten the photoperiod slightly in winter. This mimics a seasonal change without pushing the animal into full brumation. It is a judgment call, not a fixed requirement, for a tegu kept at stable temperatures year round.

Thermostats and tegu heat requirements

Every heat source in a tegu enclosure should run through its own thermostat. This includes the basking bulb, any ceramic heat emitter, and any radiant panel. Do not rely on a lamp dimmer or a bare outlet timer alone.

A quality basking bulb paired with a thermostat needs a probe at the basking surface or at warm side floor level. That probe shuts the heat off, or holds it at a set output, before overheating becomes an emergency. A burn or heat stress event can happen fast in a small mistake left unchecked.

Pulse proportional and dimming thermostats generally hold a tighter, steadier temperature than a simple on and off unit. That precision matters more as enclosure size grows. Small swings become large amounts of heat across many square feet.

Keep a backup plan on hand. A spare bulb, a spare thermostat, and a written note of current settings all help. That backup protects against one equipment failure turning into a multi day cold snap.

Tegus are strong, persistent diggers and climbers. All wiring, bulb guards, and thermostat probes need a secure mount that resists chewing and digging.

A probe buried in substrate, or knocked loose, reports the wrong temperature. That failure can let an enclosure run dangerously hot or cold with no alarm at all.

Frequently Asked Questions

What is the ideal basking temperature for a tegu?

The basking surface should read 95 to 100 degrees Fahrenheit measured directly on the material the tegu lies on. A digital infrared thermometer aimed at the basking platform gives a more accurate reading than an air gauge hung nearby.

Do tegus need 5.0 or 10.0 UVB?

Neither number alone answers the question, since the percentage only states the share of UVB in a bulb’s output. The species sits in Ferguson Zone 3, so aim for a UV Index of roughly 3.0 to 4.0 at the basking spot, which a high output T5 tube reaches at a practical distance and a low wattage bulb of any labeled percentage does not.

Can a tegu enclosure get too hot?

Yes, and it is a real risk in a large enclosure running several heat sources without independent thermostats. A cool side near 75 degrees Fahrenheit gives the animal an escape route, but only if the warm side and basking spot also stay within their target ranges.

Should tegu lighting stay on all night?

No, visible light and UVB bulbs should switch off after 12 to 14 hours of daytime light. Nighttime warmth near 75 degrees Fahrenheit should come from a source that does not emit light, such as a ceramic heat emitter on its own thermostat.

How do I know if my tegu is trying to brumate?

A tegu heading into brumation typically slows down, eats less, and seeks cooler, darker retreats as temperatures drop into the low 70s Fahrenheit. That is a seasonal response tied to falling temperature, so a sudden slowdown at a stable 75 to 100 degree setup is better treated as a possible health issue.

How often should I replace a tegu UVB bulb?

Annual replacement is standard for quality UVB tubes, since ultraviolet output declines well before the visible light dims. A monthly check with a UV meter catches a fading tube early, before weak UVB starts to affect bone or muscle health.