Metal halides are chemical compounds formed from metals and halogens. They typically consist of a metal cation and one or more halide anions, such as chlorine, bromine, or iodine. These compounds can be found in various forms, including solids, liquids, and gases, and are often used in applications like lighting, catalysis, and electronics. In the context of lighting, metal halide lamps are a popular choice for outdoor and industrial use due to their bright, white light and energy efficiency. They contain a mixture of metal halides, which produce light when an electric current passes through the gas inside the lamp.