UVB is an invisible ultraviolet spectrum of light. It is essential to all living animals, but especially to diurnal reptiles (definition: reptiles active during the day)
. Nocturnal reptiles also benefit from UVB, but it’s not as crucial. UVB light allows the body to synthesize vitamin D3, which is required to metabolize calcium. Without it, reptiles are unable to use the calcium in their diet and begin to take it from their bones which causes medical issues with their bones and nervous system and will eventually lead to death.
All reptiles should follow a day/night cycle and diurnal reptiles especially need a good amount of daytime light but they also require nighttime, where there is no bright light so they can rest. Research your specific reptile breed's particular needs, but as a general rule 12 hours of the day should have daytime light & heat as well as UVB. Those lamps should be shut off for the second 12 hours of the day but there needs to be constant heat and use of a red/black night heat lamp or heat pad so it won't disturb the animal.