An electro-negative element or radical, which, by combination with a metal, forms a haloid salt; especially, chlorine, fluorine, bromine, and iodine; sometimes, also cyanogen. See Chlorine family, under Chlorine.
Five chemically related elements belong in the halogen group. They are astatine, bromine, chlorine, fluorine, and iodine. Minerals that are composed of the halogen elements are known as halides.
A high pressure incandescent lamp/bulb containing halogen gases such as iodine or bromine which allow the filaments to be operated at higher temperatures and higher efficacies. Halogens emit damaging UV rays, which cause color fading of sensitive fabric and artworks, just as the sun would. Lamps based on Halogen technology can not be handled by bare hands without shorting lamp/bulb life. Dirt, oils, grease, fingerprints must be wiped clean with rubbing alcohol before using your halogen bulb. Drug stores always carry rubbing alcohol, the 90% is better, as the 70% alcohol is 30% water. Contaminated bulbs will blister, shorting bulb life by either a breach of the Quartz lens or the filament not burning at an even temperature. Contaminates, dirt, oils on the lens create hotspots which lead to premature failure.