Modelled on nature
Terrarium animals are cold-blooded animals, highly dependent on light, especially on the quality and intensity of the light. Activity, food intake, digestion or rest phases are influenced by the change of day and night and the intensity of light. Depending on the light source, there are differences in output and quality of the light.
Which light for which animals?
Only a few of the general statements are right. It is true that desert animals, which are active during the day, are exposed to strong UV radiation. For rainforest animals this is more complicated: As long as the animals stay under the leafy canopy of the rainforest they will have no or just very low UV radiation requirements. But whenever the animals live in the leafy canopy or at the riverbanks, their UV requirements can increase to that of desert animals! Therefore it is important that you deal with the habitat AND the habits of the animals.
An example: The tree python is a nocturnal animal and thus, at first glance, doesn’t rely on UV radiation. But it rests the whole day in the treetops and receives a lot of UV light. The decrease of UV radiation is the start signal for its activity phase. Consequently also this nocturnal animal needs UV-emitting lighting!