Since the 1980s, overhead projectors have enjoyed widespread use in classrooms, businesses and churches, but they come with limitations. Although many are being replaced with digital projectors, they still find use today, and it is important for the presenter to understand their disadvantages.
Overhead projectors are bulky, and it can be difficult to find ample space to operate them. First, there is the size of the unit itself, which can require up to four square feet on a solid surface if the projector handles larger-size transparencies. They also must be placed a proper distance from the screen to achieve optimum clarity. Finally, additional space is required for storage of erasable markers and transparencies.
While the projected image may be visible with lights on, older overhead projectors, or those with older bulbs, may produce images that are blurry due to interference from other light sources. Ideally, the room should be darkened, but this too can pose problems by making it difficult to see which transparency to load next, or finding markers to make notes on the transparency.
Even small projectors can weigh over 30 lb., and the larger models can easily weigh 80 lb. or more. This can make it difficult to transport the unit from one room to another. Another consideration is that the projector must be placed on a surface that can support its weight.
Perhaps the biggest disadvantage to overhead projectors is the cost of the materials required to operate them. Transparencies cannot be reused unless you're using dry-erase markers, and can become stained over time if they are not cleaned properly. New markers must be periodically purchased as well because they run out of ink. Finally, the bulb in the unit will need to be replaced every couple of years, and they are significantly more expensive than standard light bulbs.