Zoo Med's ReptiSun Terrarium Hood is designed to fit terrariums 20" wide and up (10 gallons or larger). This hood can hold one 18" T8 linear fluorescent lamp. UVB is needed by reptiles for proper growth and maintenance of strong bones. Without UVB (and the appropriate temperatures), your reptile can develop metabolic bone disease which results in soft, rubbery bones within 6 months. Dimensions: 20.25"L x 4.25" W x 2"H.