Mog or Mogul Base: The base of the metal halide bulb usually 175 Watt through 400 Watt. The diameter is roughly 2". The US standard is size E39 and the European standard is E40. The E39 base is slightly larger than the E40 base. Usually there are few problems screwing in the European E40 base lamp into the US E39 socket. The reverse of this is not true.

Med or Medium Base: The base of the metal halide bulb usually 70 Watt through 150 Watt. The diameter is roughly 1 3/8". The US standard is size E26 and the European standard is E27. The E26 base is slightly larger than the E27 base. Usually there are few problems screwing in the European E40 base lamp into the US E39 socket. The reverse of this is not true. Do not use incandesent sockets on metal halide bulbs.

Color Temperature: Color temperature, expressed in Kelvins (K) is one way to describe color tone. The higher the color temperature, the bluer the light appears.

Lamp: Another term for light bulb.

Metal Halide Lamp: A high-intensity discharge light source in which the light is produced by the radiation from mercury, plus halides of metals such as sodium, scandium, indium, and dysprosium.