The Science Behind Projector Lamp and Bulb Technology
The High Intensity Discharge Projector Lamp Burner
A projector or DLP television lamp module contains a High Intensity Discharge projector bulb (HID projector bulb), which is also referred to as the projector lamp's burner. The name High Intensity Discharge means that this type of projector bulb functions by producing light from a small yet very powerful electrical discharge. This is different to a normal fluorescent lamp, which produces light from a larger but less intense electrical discharge. The small, intense electrical discharge between the two electrodes in a High Intensity Discharge projector bulb causes the metal halide atoms contained within the bulb to glow, producing the projector's light output.
Projector Bulb Technology Seen In The Natural World
The electrical discharge in a projector bulb which causes the metal halide atoms in the projector bulb to glow is the same kind of effect that we see during a thunder storm. The lightning that we see during these electric storms is really just a high intensity discharge on a much larger scale, and with different gases involves. Instead of the metal halide gas in the projector bulb glowing, the high voltage that is discharged from storm clouds to the ground through the air causes the nitrogen atoms in the air to glow, producing a lightning strike.
Metal Gases Producing Light
Projector bulbs use a mercury halide gas mixture to produce light when these atoms are excited by an electrical current from the projector's power source. The basis for using a mercury halide gas is because this type of gas has an extremely high vapor pressure, and also has an increased percentage of emission in the spectrum of light that humans can see. This phenomenon was originally discovered by scientists performing flame tests on metals in the laboratory. These scientists found that when a metal is applied to a naked flame, different colours of flame are produced depending on which metal is used. Ordinary table salt, for example, contains sodium atoms which are excited by the heat to produce a bright orange coloured flame. When scientists first witnessed this phenomena, they tested other metals and found that mercury halide atoms glow a bright white when excited: perfect for producing light in an optical device like a multimedia projector.
The Inventor Of The Metal Halide Projector Lamp
The original inventor of the metal halide projector lamp was Dr. Gilbert H. Reiling, who made his discovery in 1962. Metal halide projector lamps can be further classified as "High Intensity Discharge" lamps and "mercury halide" lamps as well. The distribution of the three primary colors of light (red, green and blue) produced by all metal halide lamps is excellent, meaning that the bright white light that a metal halide lamp produces can compare to natural daylight, in terms of its colour rendering attributes.
How A Projector Lamp Functions
During the operation of a High Intensity Discharge metal halide projector lamp, light is generated by an electrical discharge between two electrodes in the middle of the projector bulb which causes the mercury atoms inside the bulb to glow. Metal halides are used simply because the metal atoms in a non halide form frequently do not have a sufficient vapor pressure to be discharged. Halides, on the other hand, vaporize much more easily, and have the benefit of being much less reactive than metal atoms by themselves, which means that corrosion of the projector bulb is minimized.
Why Are Replacement Projector Lamps So Costly?
Although the basic method in which bulbs inside projector lamps and normal fluorescent bulbs produce light is similar, the actual technology involved in producing light in a High Intensity Discharge bulb is quite different to that in a fluorescent lamp. The light output from a High Intensity Discharge bulb is much higher, and so the temperature and pressure stresses that the projector bulb must operate under are much higher too. The extreme temperatures and pressures mean that a high quality quartz must be used to manufacture the projector bulb to make sure that resistance to these temperature and pressure stresses is possible while still providing a very high quality light output from the bulb. The mercury gases that cause the projector bulb to produce its light are also much more expensive than the gases used inside a normal fluorescent bulb. In addition, the actual projector bulb may be blown by hand during the manufacturing process to ensure complete precision.
For these reasons, projector lamps often cost a lot more than light bulbs used for everyday purposes.
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