Ultraviolet “B” light (280-320 nanometers) is primarily used in the production of D3. It is also important to the removal of excess D3. D3 is used to assimilate Calcium and Phosphorus into bone.

UVB is produced in bulbs containing mercury. Only bulbs that are made with quartz glass and coated with phosphor compounds can emit UVB. The more or less phosphor determines the amount of UVB emitted. These compounds break down over time. Always read the manufactures suggested replacement time and mark the bulb with the date of installation.

What % of UVB you use depends on the reptile. Most Forest dwellers are fine with a 5% bulb. Desert species may need up to a 10% bulb. Some nocturnal reptiles benefit from indirect UVB. For these 2% bulbs can be used. They will help regulate photoperiods as well.