How many hours of UVB per day

The table

Why photoperiod is worth bothering with

It regulates the day and night cycle, which supports circadian rhythm, seasonal cycling, activity and appetite. For leopard geckos specifically the guidance notes that having a light on during the day helps regulate that cycle, which is good for mental health and stimulates appetite. These are not marginal effects - inappetence is one of the most common reasons keepers end up at a vet, and lighting is one of the cheapest variables to get right.

Running it on a timer

A plug timer is sufficient. A smart timer synced to local sunrise and sunset is better, because it produces the seasonal drift automatically rather than requiring you to remember twice a year. The published leopard gecko suggestion is to bring the UVB on 59 minutes after sunrise rather than at the same moment as the daylight lamp, which approximates the way UV intensity ramps in the morning rather than arriving all at once.

Seasonal change is a feature, not an inconvenience

Reducing light hours in winter simulates the change of seasons. For crested geckos the published swing is large - 14 hours down to 10 - and it supports seasonal cycling. A fixed 12 hours year-round is better than nothing, but the seasonal version is closer to what the animals evolved under and costs no extra equipment.

Daytime illumination separate from UVB

For a bearded dragon the guidance adds a separate requirement: bright approximately 6500 K illumination covering 75 to 100% of the enclosure length, which may need more than one lamp. That is a third lighting channel on top of UVB and basking heat, and it is the one most setups omit entirely.