Determining your projector's brightness
Relating visual impact to screen size and room lighting levels
There’s no simple way to choose the brightness you need when you buy a projector. The quality of the image can be predicted by a formula relating screen size, screen gain, projector brightness, contrast ratio, and the ambient light level of the room. Most often engineers and buyers specify the projector using their own judgment and experience.
Brighter is not always better when you buy a projector. It’s very possible to buy one so bright that it washes out detail or is uncomfortable to view.
When you consider brightness, realize that the blacks in your image can never be darker than the screen material you project on. In a well lit room, white or gray material will never look black, so, in theory, you’ll always get the best image in the dark. But in reality your eye will be fooled by the projector’s contrast. Unless the image is very dark –for instance, a movie scene shot at night– you can get very good results in high ambient light.
Realize, too, that screen size is critically important to projector brightness. With a larger screen, you’ll need to spread the projected light over a larger area, and brightness will fall proportionately. Before you decide on the brightness of your projector, you’ll have to calculate the size of your screen.
We present this chart not as the last word in choosing projectors, but as a guide designed to help the average buyer benefit from our knowledge and experience. Often a lower-lumen projector will be acceptable to many users, but when you want superior image quality, follow these guidelines.
Other factors to consider
Here are a few more rules of thumb that can help with your projector choice:
In making this chart, we assumed that you will use a matte white screen or a rear projection screen with a gain of 1. If you’re using a screen with a different gain factor, say .8 or 1.5, simply multiply the brightness of the projector by the gain to get the new, apparent brightness at the center of your seating area.
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