The heart of the projector is its lamp, which is its primary component. This lamp is accessible in most of the models behind the projector door, for easy replacement. At times projectors come equipped with two lamps, both of which function together, or one may take over when the other one fails. You may have come across the term UHP when purchasing a projector. This stands for Ultra High Pressure lamps which are commonly used in projectors, the other lamps are metal halide, and, for larger and upper range projectors, Xenon lamps. Xenon lamps give better color images than metal halide, but need more energy to operate and have a lower life span. What is being called the lamp is actually an entire lamp module comprising of the bulb, the reflector both encased in housing with leads for power reception.

There is an integrator which receives the light of the bulb which is thrown on it by the reflector, through a system of lenses. It is a very efficient system that processes the image to appear sharp and all the pixels are uniformly illuminated without wastage of light. The reflector is designed to process all the light optimally. This is a very sophisticated system which a layman does not need to understand, but, I am given to understand that many papers are written about the system by technical people dealing with the science of optics and photography.

What a end user of the projector needs to know and understand is that the reflector concentrates the light from the projector bulb through a series of lenses or a single lens so that as much light as possible can be delivered on the screen, so that we get extremely sharp and life like images.

Bulb size and the problem with stray light rays

The manufacturers noticed problems arising from stray light rays. These, since they were not directed directly on the screen, reduced the efficiency of the projector by striking various other walls of the projector and also leaking through the vents. If they escaped the projector they could strike the screen in various places affecting the image and the color. So innovative minds worked at this problem and found a solution, which is to reduce the source of the light. The theory is that smaller the light source, smaller the leakage, hence the size of the projector bulbs started getting reduced.

Innovative ways to make the small bulb create a great illumination have been adopted. For instance metal halide lamps have a gas filled gap through which light is created. However this has led to unwanted tungsten deposits that darken the lamp and reduce its brightness. UHP lamps were introduced by Philips which employs a pure mercury vapor arc under extremely high pressure to create illumination. The arc gap is smaller than the halide gas filled gap, and sidesteps the tungsten deposit problem. It also creates much better light.