Repta-Sun Incandescent Lighting For Basking Animals. Repta-Sun Incandescent light bulbs provide the radiant heat (infrared light) that reptiles need. Reptiles are ectothermic and depend on their environmental temperature to regulate their core body temperature. If a reptile is not provided an appropriate environmental temperature range (ETR) it may be predisposed to chronic infections. Because ETRs vary from species to species ask your pet professional or review available literature for guidance in determining the appropriate ETR for your pet.