How Projector Lamps Work
Projector lamps come in many shapes and types and are the most frequently replaced part in projectors. A few projector lamps are available to both commercial and residential consumers. The capacity in which the projector is used will determine the appropriate lamp to choose.
o Overhead projectors use a special type of incandescent light called a halogen light. Incandescent lights work by running an electric current through a thin tungsten filament. The filament resists the flow of the current, turning the electric power into heat. As the filament heats up, it begins to glow, which is what creates the light.
o The halogen bulbs used to create the light in projectors are a bit different than normal incandescent lights in a couple of ways. Normal incandescent bulbs leak a lot of heat, wasting a lot of energy. Halogen bulbs use quartz crystal instead of normal light, which works as an efficient insulator. More of the heat is trapped inside, heating the filament to higher temperatures, and causing it to produce more light for the same amount of power.
o Another advantage of halogen bulbs has to do with the gas in them. In normal incandescent light bulbs, the tungsten slowly evaporates from the filament, coating the inside of the bulb. This darkens the bulb, lowering the light output. It also wears out the filament, causing the bulb to burn out more quickly than it otherwise would. The higher temperature in halogen bulbs, combined with a special gas in halogen bulbs, creates a reversible reaction different than in incandescent bulbs. The iodine will still evaporate, but as it cools it tends to be deposited back on the filament. This stops the filament from thinning and wearing out as quickly, and keeps the inside of the bulb clear