A light is not a light without a light source. The theatrical world commonly uses instrumentation that either use incandescent, quartz or gaseous lamps. The industry is also transitioning to LED units which use diodes. - Louie Lumen
A three letter system that has been devised to describe lamps of different manufacture but the same application.The letters have no relationship to lamp description, but the same letters always designate the same type of lamp.Some of the application parameters they define are wattage, base type envelope size, and light center length.