The different types of projection bulbs can be categorized based on the devices they are designed for or the method the lamps use to generate light. Projection bulbs are required in a variety of different equipment, from overhead projectors used in instructional settings to television sets and other devices used for entertainment. Each of these devices requires a different type of projection bulb to operate. There are also many different technologies used in these bulbs. Most projection bulbs were once halogen lamps, though xenon arc and metal halide have become more popular choices due to factors such as longevity and brightness.
Any device that projects a small image onto a large screen by using a light source requires some type of projection bulb. Some of the simplest devices that operate on this principle are overhead projectors, which send light through a transparent picture and then uses a mirror to enlarge the image and impose it on a screen. Similar devices that are found in entertainment, instructional, and business settings are used to convert video signals into an image that can be projected onto a screen. Rear and front projection televisions also require lamps.
The most commonly used projection bulbs contain halogen at one point due to the bright light they were capable of producing. Halogen lamps operate at very high temperatures and can produce a yellow-tinted light that may not be desirable for some applications. One common use of halogen bulbs was in overhead projectors, which typically had powerful fans to keep the lamps cool. Over time, these lamps were replaced by various other technologies.
Another type of projector bulb uses an electric discharge through a metal-halide to generate light. These projection bulbs are sometimes referred to as ultra high performance (UHP) or other names, and often contain mercury vapor. Metal-halide lamps are capable of producing bright light with a full color spectrum that eliminates the yellow tint associated with halogen bulbs, and they can last around 10,000 hours before a noticeable degradation in quality appears. Various types of metal-halide lamps are used in televisions, projectors, and other devices.
Many of the projection bulbs found in theaters use xenon arc technology. These lamps are filled with ionized xenon gas and can create very intense white light. Depending on the application, these bulbs are capable of putting out between 900 watts and 15 kW.
Some projectors and televisions also make use of light emitting diodes (LEDs). Instead of a single high powered projection bulb, these devices use an array of LEDs that can put out roughly the same amount of light. Most projection bulbs have a half-life of between 10,000 and 20,000 hours, though LEDs can last substantially longer.