The Exo Terra Night Heat Lamp is a dark blue incandescent bulb designed to provide low-intensity nighttime heating.
As with red bulbs, blue "moonlight" bulbs are largely unnecessary for reptiles, and may even be potentially harmful. Nocturnal reptiles have wonderfully sensitive eyes that allow them to see perfectly well in what is total darkness to humans, so supplemental nighttime lighting is largely unnecessary. Furthermore, providing light at night can negatively affect a diurnal (day-active) reptile's quality of sleep, and blue light in particular is known to have negative effects on eye health and circadian rhythm.
If you need a nighttime heat source due to nighttime temps too cold for your reptile's needs, we recommend the Exo Terra Ceramic Heater as an alternative.