Mega-Ray Mercury Vapor Bulb - 100 Watts (120V) provides the necessary UVB, UVA and heat for your UVB-dependent basking reptiles disperse usable UVB in a 30" circumference at a 20" distance MINIMUM distance setting of 12" will produce approximately 150-200 microwatts per square centimeter (uW/cm2) of UVB and 900-1200uW/cm2 of UVA MAXIMUM distance setting of 20" will produce 50-75 microwatts per square centimeter (uW/cm2) of UVB &#9989 Use with recommended fixture, such as a wire clamp lamp. Not to be used with dimmers or rheostats.