Each projector has a brightness rating expressed as ANSI lumens. ANSI is simply a standard method of measuring lumens. It was introduced so that you could easily compare one projector's brightness with that of other projectors. A typical classroom projector is likely to need somewhere between 2,000 and 3,000 ANSI lumens.
Projectors with a higher ANSI lumen rating will cope better with the onslaught of ambient light coming in through your windows and from ceiling lights. However, a word of caution: position the projector so that neither you nor your students are looking directly into the projector light, especially from a close distance.
If you plan to project onto an interactive whiteboard with a glossy surface rather than a projection screen, be aware that a highly reflective smooth surface may cause glare and the brighter the projector the greater the glare.
Projectors generate heat and the brighter the projector the more heat it will generate. Projectors are cooled with internal fans and the movement of the fan will produce audible noise. Some projectors mitigate this noise by enlarging the enclosure to make it easier to move air. Check the audible noise rating in the projector specifications. This number is measured in decibels (dB) and the lower the number the quieter the projector. As a point of reference, a decibel rating of 30dB is about the noise level of a library.
Things to Consider When Choosing Brightness
There are five primary considerations when choosing your projector's brightness.
- How far away is your farthest student? This determines the size of the projected image that is required for easy viewing by everyone present. The larger the image the brighter the projector must be in order to maintain a readable image. As a rule of thumb, the height of the screen should be about 1/6 the distance to the farthest student.
- How much light is in the room? A dark room will provide the best image regardless of projector brightness. However this is not ideal in an academic environment where interaction is the goal and some lighting for note-taking and eye contact is essential. A classroom where the lights cannot be turned off or dimmed from within the room or where the windows cannot be blocked or covered will require a bright projector. That same bright projector placed in a perfectly dark room may cause eye strain; however, most projectors offer an economy mode that allows you to reduce the brightness of the projector by 20% and at the same time extend the life of the lamp.
- What kind of projection screen will you be using? Many of today's projection screens allow light striking the screen at extreme angles to be absorbed by the screen rather than reflected. This helps to maintain the image quality by removing competing light and maintaining contrast and image quality.
- What is screen "gain"? A screen reflects a fixed amount of light. Where that light is distributed is determined by the gain of the screen. A screen with a gain of 1 provides the greatest viewing angle. This means students to the left and right of the screen can easily see the image. Screens with gains higher than 1 increase the brightness of the image toward the center of the room at the expense of a dimmer image to the sides of the room. This means higher screen gains have a narrower viewing angle. A gain between 1 and 1.5 is suitable for a classroom. If you need to go to higher gains, check with your installer or screen supplier.
- Can I use a wall or chalkboard for a screen? Yes, you can; however, image quality and brightness will suffer. Many of today's projectors, offer a Blackboard mode. When in this mode the projector determines the quality of the projection surface and attempts to optimize the color accordingly. If this is an option you would like to consider, seek a demonstration to be sure that you are satisfied with the results. Click here to see projectors that offer Blackboard mode.