Projection screens can become yellowed because of environmental effects on the screen surface, such as smoke. More often, it is a problem that results in the projector reproducing an image with incorrect colours. This could also be an internal issue with the projector or a problem with the video signal coming into the projector. Discovering the variables that cause a yellow appearance on a projector screen will also help you troubleshoot the source of the problem and reduce the chances of it happening by exercising some simple preventive measures.
The cable that connects the projector to the source of the video signal could be faulty. If using a VGA cable, it is possible that there is a bent pin on one of the connectors preventing a colour from being displayed on the screen. An intermittent connection on a VGA or BNC twist-on type connector would cause the same problem.
The lamps used in projectors are rated for a certain number of hours of use. This rating is an approximate value and the actual life is dependent not just on the amount of hours used, but the number of times the lamp was turned on, or "struck." The higher the number of hours on the lamp and the more times a lamp is struck, the lower the intensity of the lamp and the more discolouration in the projected image.
Projectors have cooling fans that run and draw air through them which in turn brings a certain amount of dust and other environmental elements into the projector. If using a fog or haze machine, the results are accelerated. Dust and film build-up on the internal optics can cause discolouration and a loss of image clarity. Check for dust build-up by adjusting focus in or out until the debris on the internal optics comes into focus. Removing build up requires disassembly of the projector for cleaning.
Bad Optical Components
Within an LCD projector, there are polarisers that control the colours when they pass through the LCD panels. Over time, these panels can fail to pass colours properly and uniformly. Polarisers generally fail gradually and are identified by spots of discolouration, then eventual full-screen discolouration.
Projectors can have a longer lifespan when properly maintained and cared for. Most projectors have air filters at the air intake vents. Frequent cleaning of these filters will allow for cooler operation, more effective filtering and cleaner internal optics over time. Leaving the projector running creates less wear on the lamp than turning it off and having to restrike the lamp if it is only unused for a few hours. If the projector is not needed for more than four hours, it would then be beneficial to turn it off. The striking of the lamp has a significant impact on the lamp life. LCD projectors as compared to DLP projectors will have a slightly green and yellowish tint to the image. DLP projectors replicate colours more accurately, with less yellowing of the image due to different internal processing of the video signal.