Zoo Med's new 18 inch ReptiSun Terrarium Hood is designed to fit terrariums 20 inches wide and up (10 gallons or larger). This hood can hold one 18 inch ReptiSun Linear Fluorescent lamp. A built in reflector allows for deeper penetration on visible light and UVB into your terrarium. UVB is needed by reptiles for the 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. Reptiles and amphibians can see things illuminated by UVA lighting that people can't. UVA is important for the psychological well being of reptiles and amphibians.