Do crested geckos need UVB?

The honest version of the answer

You will be told crested geckos do not need UVB because a high-quality prepared diet supplies the D3. The guidance we cite accepts that not having UVB will not necessarily kill a crested gecko - and then recommends it anyway, on the grounds that there is a growing body of evidence that providing UVB substantially increases health and quality of life for reptiles previously thought not to need it.

There is a second argument that has nothing to do with vitamin D: UVB bulbs also emit UVA, which reptiles see as an additional color. Keeping an animal without it is a visually impoverished environment in a way that is easy to overlook because we cannot perceive the difference ourselves.

The dose

Target UVI 1.0-2.0 at the basking branch at the branch, measured with a Solarmeter 6.5. Because crested geckos are arboreal, the "basking spot" is a branch near the top of the enclosure rather than a rock on the floor - which means the distance you care about is from the lamp to that branch, not to the substrate.

The temperature point that matters more than UVB

For this species, heat is the bigger risk than light. Target 82-85 F (28-29 C) at the top of the enclosure at the top of the enclosure and 70-75 F (21-24 C) at the bottom at the bottom, with nights at 65-72 F (18-22 C). Sustained temperatures above 85 F can cause stress and heat stroke; at or below 72 F you get lethargy, poor appetite and illness. In many homes a crested gecko needs no supplemental heat at all, and adding a lamp without measuring the room first is the more common mistake than omitting UVB.

Photoperiod

14 hours in summer, 10 hours in winter, preferably with gradual transitions. This supports circadian rhythm, seasonal cycling, activity and appetite. Do not run any light at night - crested gecko eyes function perfectly in the dark, and night light disrupts the cycle.

The full crested gecko lighting setup is here, and the temperature and humidity page covers the ceiling.