Any of the non-metallic elements fluorine, chlorine, bromine, iodine, and astatine existing in a free state – halogens are enclosed within the arc tube of a Metal Halide (MH) lamp.
Merriam-Webster Online Dictionary
halogen (noun) any of the five elements fluorine, chlorine, bromine, iodine, and astatine that form part of group VIIA of the periodic table and exist in the free state normally as diatomic molecules
containing, using, or being a halogen - a halogen lamp
halide, reactive nonmetal, group 17 element, fluorine family, salt-former
