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Projector Terms ANSI Lumens Resolution Contrast Ratio Throw Distance

What the heck do all those numbers mean? There’s a lot of numbers associated with video projectors. Here is a brief rundown of what they mean and why they’re important.

ANSI Lumens

Dictionary.com defines “lumen” as “Abbr. lm Physics. The unit of luminous flux in the International System, equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions.” Essentially, this means that a lumen is the measurement of light given out by one candle at a distance of one foot. Obviously, you need a lot of candles to create a lot of light. ANSI stands for “American National Standards Institute”, the governing body over such things as measuring actual light output. Before ANSI standards, projector brightness was measured at the center of the projected image, with significant drop-off toward the edges. The newer ANSI standard breaks the screen into 9 parts, with brightness being measured as an average over the entire surface of the projected image, instead of just at the middle.

Is brighter better? Not necessarily. Most home theater projectors max out at 1000 ANSI Lumens or so, while a decent business projector is twice that, or more. The difference is because the people who design these projectors have determined that you have more control over ambient light in your home. You don’t have to compensate for a wall of windows in a boardroom, or keeping the lights on so you can scribble notes. Instead, you’re probably trying to replicate the kind of experience you get in a movie theatre. Psychologically, we’re more likely to be immersed in an image that isn’t competing with other visual distractions. Dimming the light levels on all other objects in our field of view, other than the screen, actually improves our perception of it.

Resolution

The actual number of pixels, or individual picture elements, measured in columns and rows. Resolution will vary, on a 16:9 projector, generally from 850x480, 1024x576, to 1280x720. Note that while the actual pixel numbers change, the ratio remains the same – 16:9. Pixels are arranged in a grid like pattern. The larger number is the left to right pixel count, the smaller number is the top to bottom. The higher the resolution, the greater the detail (or so it would seem… see “Contrast”, below). True HD starts at 1280x720, and goes all the way to 1920x1080. A home theater purist would probably opt for the native 1280x720 display, other considerations not withstanding. This is a big thing right now in the HT crowd: pixel matching. One pixel on the source image equals one pixel in your home. I personally won’t say that you’ll get a “better” picture pixel matching. IMHO there are too many other important factors that go into creating a bright, vibrant, beautiful picture.

Contrast Ratio

The most important number associated with projector performance, and also the most misunderstood. Simply put, contrast ratio is the relationship between the brightest and darkest point of a given image, measured in discreet steps. The farther apart the numbers are, the greater the detail in the darker areas. As a result, larger contrast ratios imply better picture.

Now, this is where it gets tricky… remember that brightness measurements are standardized, largely as a result of poor practices by projector manufacturers of the past, in rating the brightness of their projectors. Currently, contrast measurements are not standardized – everybody uses methods and formulae that are advantageous to them. As a result, ignore this number. It’s not a good indication of projector performance, and won’t be until everybody starts using the same methods. To illustrate, the Da-Lite Screen Company, suggests “… the contrast of the page before you is about 80:1. If you are looking at them on a monitor, the ratio is closer to 50:1. If you go to the movies and watch a good, clean print, the ratio, given the right scene, might be 500:1.” (“Angles of View”, Volume III, Contrast – From Dark to Light).

Throw Distance

Indicates the minimum and maximum distance between the projector and the screen. Don’t rely overmuch on these numbers. The idea is to achieve the largest possible picture (which is a function of throw distance) while retaining excellent picture characteristics, like brightness, colour saturation, etc. Rather than using these numbers, consult with an AV professional who can help you determine what image size, and projector location, will work best for you.

Bottom line? It’s not all about the numbers. They only tell you so much, and in certain cases, like contrast ratio, they tell you very little. I’ve seen projectors that, on paper, aren’t particularly impressive, but get them out of the box and playing a movie, they really shine. Pun intended.