Do terrarium animals know when they have received enough UV radiation? Or in other words: Do the animals withdraw into the shade after they have received sufficient UV radiation from the UV light source or can they get sunburn?
Here it depends on the species and behaviour. Animals which can be exposed to too much UV radiation in the wild, like mountain animals (some chameleon species are examples of this), know when they have received enough UV-radiation. This is based on a variety of factors (amount of light in lux, humidity). Other animal groups, such as those living on the ground in the rain forest, never receive too much UV radiation in their natural habitat. These animals would be harmed by permanent, strong UV radiation.