What wattage heat bulb for a reptile?

Why the question has no fixed answer

A wattage figure is a power draw, not a temperature. The same 75 W halogen lamp produces a very different basking surface temperature at 8 inches than at 16, in a 36 inch glass tank than in a 4 ft PVC enclosure, in a 78 F room than in a 62 F one. Any guide that gives you a single number per species has silently assumed all three of those variables and has not told you which ones.

The published figures are surface temperatures, so that is the variable to control. Wattage is just the dial you turn to get there, and the thermostat is what holds it once you arrive.

The figures to actually hit

A sane starting point, then measure

Start low rather than high - it is easier to add wattage than to recover an animal from an overheated enclosure. Broadly: a small enclosure with a short lamp-to-surface distance starts around 50 W, a 4 ft enclosure with a mesh top and a 12 to 14 inch drop starts around 75 to 100 W, and a cold room pushes both up. Published guidance for a crested gecko basking area, for example, names a 50 W halogen in a 5.5 inch dome.

Then take a surface reading at the basking site with the lamp at working height and the thermostat set, wait for it to stabilise, and adjust. Adjust distance first, wattage second - raising or lowering the lamp is free and reversible.

The thermostat is not optional, and the type matters

A heat source without a controller will keep heating, and the ways that ends are all bad. The controller type has to match the source: a light-emitting lamp needs a dimming or pulse-proportional unit, because an on/off controller will strobe it visibly and shorten the filament's life. An on/off controller is acceptable only for a lightless source such as a ceramic emitter, a radiant panel or a mat. That is the whole decision, and it is laid out in which thermostat each heat source needs.

Daytime and night-time are separate purchases

Halogen is what current guidance prefers for daytime basking, because it produces more Infrared-A - the deeply penetrating band - than a ceramic emitter does. It also emits visible light, which makes it unusable at night. If your room drops below the species night minimum, night heat is a second, lightless source rather than a different wattage of the same lamp. The two lightless options are compared in radiant heat panel vs ceramic heat emitter.

And before you buy a night source at all: measure the room overnight. A leopard gecko tolerates a fall to 60 F and a bearded dragon's night range runs to 55-75 F (12-24 C), so plenty of homes need no night heat whatsoever.

What never decides wattage

• Gallon rating. It is a volume, and it hides both the lamp drop and the floor area the heat has to cover.
• Whatever came in the kit. Starter kits are built to a price, not to your room temperature or your lamp height.
• A colored bulb. Red and blue night bulbs are a product class we do not recommend at any wattage - see night lighting mistakes.
• A mercury vapour combination bulb, run without a meter. Combining heat and UVB in one bulb removes your ability to adjust either without moving the other.

Fire safety scales with wattage

A higher-wattage lamp is hotter at the fixture as well as at the basking site. Use a ceramic socket rated for the wattage, keep a cage guard on anything the animal can reach, and keep combustible material away from the dome. Heat lamp fire safety sets out the three failure modes in detail.