Lumens: Projector brightness is measured in ANSI lumens. The higher the rating, the brighter the projected image. Front projectors start as low as 1,000 lumens and can reach an output of more than 2,500 lumens. For larger audiences or larger images, a higher lumens rating is necessary. Ambient light: Projectors with a lower brightness are perfectly adequate for lights-off presentations. However, if you present in rooms where ambient light is difficult to control, or if you want the advantage of presenting to your audience without turning off the lights, you'll require a projector with an output of at least 1,500 lumens. Audience size: The size of your audience also affects how bright your projector needs to be. Larger audiences require larger images, which also require higher lumen output. For larger presentations, brighter projectors outputting 2,000 lumens or more are quickly becoming the industry standard. Deciding on brightness: For low ambient light situations, 1,000 lumens is enough. For rooms with some ambient light, 1,500 lumens is the standard and the minimum for larger presentations. For presenting in ambient light, >2,000 lumens is recommended--and is ideal for large audience presentations. For presenting bright ambient light, >3,000 lumens is recommended--and is ideal for large churchs, board rooms, or auditoriums. Lumen Guide Below is a fast and easy reference for you to use to help determine how bright a projector you need for your room. 4:3 Screen Screen Size/ Lumens 72" (43" x 57") 100" (60" x 80 ") 120" (72" x 96 ") 150" (87" x 116 ") 1000 1200 1400 1600 1700 2000 2200 2500 3000 3500 3700 * Controlled lighting Low ambient light Some ambient light Bright ambient light Controlled lighting - If you plan to use your projector in a room where there are no windows, such as a basement, or if you use your projector primarily at night, any of today's projectors will provide a bright image. Low ambient light - Little to no lighting entering room. Some ambient light - Some additional light in room. Slightly dimmed, windows blinds leaking some light. Bright ambient light - Windows open during daylight hours, lights that cannot be dimmed like an open office settings. Bright enough for audience note taking.