Projection Lamp Life

LCD and Overhead Projector Bulb Tips:

While these tips apply to LCD projectors, they are also applicable to OHP bulbs as well. In general, any bulb that operates hot and has a very hot filament, would survive longer with proper care.

LCD projector bulbs for the majority of the new projectors are of the "metal halide" variety. These bulbs work like an arc lamp. They require a high voltage to startup. When the bulb has heated up to a high enough temperature the voltage is reduced considerably, while still maintaining a steady arc. The bulbs are very expensive and the light output decreases as they age. A newer type of bulb known as UHP ( Ultra High Performance ) maintains it brightness, for a greater length of time, over its’ rated life. It was not uncommon for some older LCD projectors to have a bulb life of 400 - 500 hours of operation. At a bulb replacement cost today of $300.00 - $400.00, these are not very economical to operate.

Most new projectors have a bulb life of more than 1,000 hours, with some as high as 4,000 hours. Regardless of the rated life of a bulb, there are precautions that can be taken to prolong the life of a bulb. Vibration and heat are two of the biggest contributors to the early demise of these types of bulbs. When using an OHP or an LCD projector, it is important to let it cool down before unplugging the power cord or moving it.

An LCD projector has a standby mode which allows the lamp time to warm up and cool off during the power-up and power-down mode. Most OHP’s have a thermal sensingswitch which allows the fan to run after shutting off the lamp. It is important to NOT unplug the OHP, or LCD projector, until they have completed the cool-off period. Moving either type of unit, while it is hot, can cause the bulb to vibrate excessively, shortening it’s rated life. When changing an OHP bulb it is necessary to use a paper towel or tissue, to keep any oils from your fingers, or hands, from getting on the surface of the bulb.

The bulb operates so hot that a bubble can form on the glass envelope of the bulb, the gases inside can escape, rendering the bulb useless. The replacement bulbs for LCD projectors come in a module that is user replaceable, if one is very careful. Again, it is important to not touch the bulb or reflector surface on this module. It is not advisable to reset the hour counter (if equipped), on an LCD projector to prolong the life of a bulb that is in it. Some projectors will allow a manual reset, that can, in a pinch, allow one to continue using that particular bulb. If the machine has automatically shut-down, due to it’s reaching the rated hour limit, it is not recommended to reset the counter.

What should I consider when buying a monitor (CRT)?

The monitor is the part that you will be looking at most of the time, so it pays to get the right one for your purposes. You will have to decide what size is appropriate for your work. The most common monitor sizes are 15", 17", 19" and 21".

Typically, CRT manufacturers today do not specify theimage performance such as focus, convergence, and geometry, out to the edges of the tube. As a result, you have to evaluate these parameters for yourself. Also, users typically do not want their images overscanned as in TV displays, especially when using GUI's. If monitors overscanned, parts of the image near the edges of the screen may not be visible.

First make sure that the monitor has warmed up for at least ten minutes. The heat escaping from the rear of the monitor should not be much more than that generated by a color television. Some monitors are now coming with fans installed for positive ventilation. Next, adjust the brightness so that the illuminated part of the screen has the same brightness as the unilluminated border. Increase contrast to a reasonable level (fairly high) and reduce screen glare as much as possible. Now you're ready to check the following:

Focus: It is important that the electron gun be focused in the center of the screen and near the corners. The corner areas are typically problematic. Look at bright text on a dark background in the center, and in the corners of the screen. Letters should be quite legible, and pixels shouldn't bleed into each other at the screen edges.

Convergence: Look closely at white lines on a black background. If the lines are white along the edges, convergence is good. If, however, a band of another color is visible along the line, then color reproduction of small objects such as characters or lines may be poor. Even if color banding is present, the monitor may still be within the manufacturer's specification. If you can see distinctly different colored lines, chances are the monitor does not meet the specification, but color fringing, while possibly considered objectionable, is likely to be present in almost every monitor built.

Geometric Distortion: Move an object of consistent size ( a window works well) around the screen and measure its height and width with a ruler. Significant variations in the size at different locations indicate geometric distortions that may not be correctable.

Color Purity: Display pure red, green and blue and for each look for color inconsistencies in the display that may indicate poor color reproduction.

White Purity: Display a totally white screen. The brightness should be reasonable uniform and there should be no objectionably obvious colored or tinted splotches.

Bleeding: Display bright primary colored object - red, green, and blue. There should be no colored trails off to the right of the bright areas.

Moire: This will depend on resolution and size. There should be no objectionable contour lines visible in the background or smooth areas of the image.

Overall Impression: Is the image clear, bright and sharp? Remember that you will be looking at the monitor for hours at a time, and that a minor flicker may become irritating over time. When possible, look at the specific monitor you want to buy, as each monitor has undergone a calibration procedure and some may be better than others - even of the same model. This is one big advantage that local stores have over mail order companies - you can look at the monitor before paying.

Failure Rate: Inquire about failure and repair rates for each model. Sometimes retailers stop carrying products because of high returns. How long has the manufacturer been in business? Do they have a good reputation for reliability and performance? Will the retailer deal with any warranty claims, or do you have to go directly to the manufacturer? Will the manufacturer supply parts and schematics for your monitor in the future? You may not be doing the work yourself, but a monitor repair technician may need these sometime after the warranty period expires.

If you have any further questions, or would like more help on monitors, please call
Technical Services 253-361 ext. 198 or ext. 187