Thursday, February 25, 2010

Brightness vs Contrast in Home Theater Projectors

Brightness vs Contrast in Home Theater Projectors

What Is Brightness?

How much illumination your eyes perceive on the screen depends on two factors: (1) the light output of the projector, and (2) the reflective properties of the screen.
There are two common methods of measuring light in a home theater. One is the ANSI lumen rating of the projector. That measures the light energy capable of being generated by the projector itself. The second is foot-Lamberts (fL), which takes the screen into account and measures the total light that is being reflected back toward the audience. Of the two, foot-Lamberts is the better method to use for setting up your home theater. However, since that number depends on your screen size and screen gain, there is no fL specification published by the projector manufacturers.

So how much light do I need?

When it comes to home theater projectors, brighter IS DEFINITELY NOT BETTER. What you want is a projector that produces enough light to fill your screen with good contrast, but not so bright that it creates eye fatigue when viewed for any length of time.

It is safe to ignore the published ANSI lumen rating—it is irrelevant for a variety of reasons. In a dark room, a luminance level on the screen in the range of 12 to 16 fL is in the ideal comfort range.

In theory, lumens and foot-Lamberts are related—one foot-Lambert of luminance is equal to one lumen per square foot. But there is no direct relationship between the ANSI lumen ratings from the manufacturer and the foot-Lambert measurements as reported in the Calculator. That is because the Calculator factors in reduced lumen outputs for video optimization and average lamp usage, in order to estimate a typical viewing experience.

Don't Get Misled by ANSI Lumen Specs

Whatever you do, don't make any assumptions about a projector's brightness based on its ANSI lumen rating. Some models have video optimization incorporated into their ratings and others do not. That means there are projectors out there which are officially rated at 700 ANSI lumens that are actually brighter than models rated at 1500 ANSI lumens. So the spec sheets, as far as lumen ratings are concerned, tend to be meaningless for home theater.

What is contrast?

Contrast is the difference in brightness between maximum white and deepest black in an image. The greater the difference, the higher the contrast.

Why is Contrast so important?

With business projectors, lumen output is of primary importance, and contrast is a secondary concern. Home theater projectors are the exact opposite. Contrast is arguably the SINGLE MOST IMPORTANT MEASUREABLE QUALITY in a home theater projector. A high contrast projector produces a picture with a rich, dynamic look, good shadow definition, and deep color saturation. Contrast gives "depth" to video images. A projector with excellent contrast can make a two-dimensional image appear almost three-dimensional.

Contrast Ratios

The contrast ratios noted on a projector's spec sheet can be reported in one of two ways. If it just says "Contrast," it usually indicates On/Off contrast, which is the ratio of the whitest white and the darkest black that the projector is capable of producing. If it says "ANSI contrast," the ratio has been determined by displaying a checkerboard pattern of white and black squares and measuring the relative brightness of each. On/Off contrast is always a larger number, and more typically listed on projector spec sheets, but ANSI contrast is a more accurate representation of what your projector is actually capable of during normal use.

Typical Contrast Specifications

Some typical On/Off contrast figures for home theater projectors are as follows:
• 3000:1
There are many entry-level projectors rated at 3000:1 on/off contrast. 3000:1 is typically enough to give satisfying black levels and color saturation, enough to avoid the sense of flatness or muddiness in a picture.
• 6000:1
Projectors rated at 6000:1 are usually capable of better blacks than 3000:1 projectors, and shadow details are better defined. In today's market, 6000:1 represent the midrange of performance for good home theater projectors.
• 50000:1
As of this writing, if you want the best contrast that money can buy, you want a projector rated at 50000:1 contrast or higher. These projectors offer deep, inky black levels and excellent shadow detail that should be sufficient for even the most demanding content.

Dark Room Needed for Best Results

You've noticed that commercial movie theaters are dark, including dark ceilings and walls. That is because any front projection system looks its best when there is no light in the room. Once you introduce ambient light into the room, that light will hit the screen and make blacks look more like dark gray. This reduces the contrast of the image, and makes it look flat or washed out. And this will happen no matter what the contrast capability of your projector is.


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