OPTIMIZING YOUR VIDEO DISPLAY
by George McKechnie
In the Gallery, we provide an overview of the different flat-panel and projector technologies available today for displaying video in a home. Here, we’ll help you choose the right video display for your purpose, by looking more closely at the factors that determine success in Home Theater installation: selecting the right technology, the display size (relative to viewing distance and seating arrangement), screen brightness, and the all-important control of ambient light.
- Screen Size. If you sit too close to a digital display, you’ll see the pixels. This is not good, as the human brain is accustomed to experiencing the nice, continuous images of nature and everyday life, not ones broken up into the picture elements that make up the scene. Today, a scan rate of 1080p (progressive) is standard, but 4K (ultra high definition) displays are selling briskly in the marketplace and are rapidly becoming the dominant technology.
- Until true 1080 progressive scan HDTV replaced 480p and 720p resolution a few years ago, it was easy to determine the best screen size for your viewing distance. You could simply put an high-definition image on the screen, view from a close distance, slowly move back until you could no longer see the pixels, then a bit further until the fuzziness disappeared. This would be the nearest viewing distance for optimal image quality.
- If you try this today with even a 1080p screen, you’ll wind up at a distance that is too close for comfort, even though it looks great. The limiting factor is eye muscle strain. If the screen is too wide for your eyes to take it all in without continually moving left and right, they will get tired. It’s like sitting in the front row of the movie theater.
- Viewing Angle. Whichever display type you watch, the best seat in the house will always be in the middle horizontally (left to right) and vertically. This should also be the sweet spot for audio performance. For Plasma TVs, off-axis viewing is superb (one of their main selling points), although the technology has largely been replaced by LED TVs. For LCD and LED TV’s, off-axis viewing (both horizontally and vertically) has improved dramatically (think of early LCD screens on laptops for reference). And even if you don’t pay a price visually for sitting off axis with a LED or LCD today, the audio balance will be less than ideal.
- For a projector system, the maximum acceptable off-axis viewing angle depends on the reflectivity of the screen—known as Gain. A low-gain screen (e.g. gain of 1.0) reflects the light back into the room widely, so that viewers sitting off-axis will see about the same image brightness as those in the perfect spot. High-gain screens (e.g. gain of 2.5) are different. They are used where the ambient light in the room is bright, and cannot easily be controlled. This type of screen takes that same amount of light from the projector and concentrates it—reflecting it back over a narrower angle. People viewing the screen at a narrow angle will see a brighter image—to compensate for the brighter ambient light. But an off-axis viewer (one sitting beyond the manufacturer’s recommended angle of view) will see a darkened image, odd optical effects, or not much at all.
- Image Brightness. LED and LCD TVs provide a brighter picture than the old Plasma units, but the difference is not great enough to matter practically in many applications. If your room is a bit brighter than you’d like (but without any direct glare on the screen), then an LED or LCD TV may provide an acceptable image. But for a very bright room, with glare directly on the screen, none of these technologies will give acceptable performance. Better to address the problem directly: by installing window shades, tinting the windows, re-positioning lights, or mounting the TV on a swing bracket, so it can be pointed away from the glare when needed.
- For a projector, image brightness is more complex. It is determined by four factors: light output of the projector, screen size, screen gain, and viewer distance from the screen. For a given projector, a larger screen will reflect the same total amount of light, but less per square foot—which is what the eye’s retina uses to gauge brightness. A high-gain screen will look brighter than a standard-gain one, because it focuses the reflected light back into a narrower pattern—unless you’re sitting too far off-axis, in which case the image will be decidedly dark. The farther you sit from the screen, the less usable light will reach you eye.
- In designing a projector-based system, the size of the screen is usually chosen first, and is determined by the seating pattern and distances plus room aesthetic considerations. Then screen material can be chosen (using manufacturer’s specifications) that will provide even illumination across the total range of seating positions. Finally a projector model will be selected which provides the level of illumination desired for the specific use. A “movie theater” experience (with people sitting in a darkened room) will require much less light output than watching a sporting event with friends. Or a power point demonstration during a lecture.
- Experienced judgment plus careful calculations are essential here. Home theater specialists typically use a projection calculator to find solution(s) that optimize among the above factors—and to make sure the combination chosen will meet the specific needs of the consumer, and conform to room parameters.
To summarize, the final video image quality of a theater in a home typically depends at least as much upon careful design and equipment specification, than it does about the quality or the equipment per se—although superior equipment (when appropriate) will always yield the best results. For installations involving Flat Panel technologies (Plasma, LED, or LCD TVs), screen size, viewing distance, and angle of view are critical. For projector systems, screen sizes are typically larger relative to room size, so viewing position may be less critical per se, so long as the manufacturer’s specifications are observed for screen material selection. But assessing and controlling ambient light are critical, as it strongly influences projector brightness (and cost), screen gain, and ultimately viewer experience.