Fixture and bulbs in one convenient package! UVB light output promotes proper calcium absorption for reptile bone health Simulates natural daylight and fulfills photo-biological requirements of reptiles.Zilla Slimline Reptile Fixtures offers high-quality fluorescent lighting in a convenient, ready-to-use fixture. It's compact and light weight design makes it easy to install and suitable for applications where space is limited. Slimline Desert Fixtures:Slimline Desert Fixture includes a 18" Desert 25 T8 fluorescent bulb with a UVB output of 25 microwatts per second/cm2 @ 12"Ideal for Desert Tortoises.