Understanding Contrast Ratio

Self explanatory really, use a real image and see what the projector can do with the ratio between the 100% black and 100% white points.

Blacks can only be as black as projection screen is in the ambient light:
If your room is not pitch black the screen will be reflecting some light. The lighter the room the less you need worry about a high contrast ratio. If you were that fussy you would paint your walls black like the cinema.

A few points to consider before getting carried away with contrast ratio:
The eyes Contrast Sensitivity Function is around 300 for the average person, it is dependent on the spatial frequency or the gap between parts of the image that vary in contrast.

1. In lower light conditions i.e. when LUX is halved, a doubling in image area is required to maintain the same contrast perception which means brighter images look like they have more contrast and a brighter projector with a lower CR may seem better than one with less ANSI Lumens (Lower LUX reading) but has a higher CR, especially in lit conditions. If the light output from the projector isn't higher than the room average LUX the image will look washed out as CR will count for little and ANSI Lumens are king.

2. At low light levels contrast sensitivity of the eye is approximately 8% of maximum. Dark adaptation takes 25 minutes to reach 80 percent adaptation, an hour for full adaptation. (In other words the first hour of the movie is not your best in this CR battle) This is why pilots (thinking of single engine light aircraft..) use red torches when flying of a night so in case of an emergency landing they have a chance too see where they are landing. Looking at a bright white light kills your night vision. So looking at a bright scene in a movie doesn't help your eyes sensitivity to the next dark one! (Can you see where I'm going with this yet?)

3. You can get a much better score or contrast perception by looking at static test patterns however as home cinema is normally of moving pictures this too can be misleading.

4. Don't confuse dynamic range with contrast sensitivity, the eye has the highest dynamic range around better than any electronic gadget under ideal conditions you can see in bright sun light or moon light once your eyes adjust. Most digital cameras are useless in starlight.

5. This doesn't mean that a projector with a CR of 2000:1 or more isn't better than one rated at 400:1 however the perceived advantage is a lot smaller than optimistic claims the manufacturers would have you believe. Note you must be viewing under ideal conditions to see the largest variance in contrast.

Some Helpful notes on contrast:
1. Your Notebook PC is about 300:1 too.
2. Cinema is 1000:1
3. Any light in the room makes higher than say 400:1 contrast ratio academic.
4. The loss of contrast sensitivity accelerates with age, at 60, the amount of light reaching the photoreceptors is only 33% of the amount seen at age 20. By the late seventies, the amount falls to 12%.
So what are we saying here?

Don't get all carried away with big contrast ratio numbers, your eye is the limiting factor, that and the amount of ambient light in the room. We haven't even touched on the source material.

The size of your projection room (how close the walls and ceiling are to the screen) plus the paint colour, carpets and fittings can change the ACTUAL contract ratio by at least a factor of five! I haven't yet seen a Home Theater room that didn't decrease the actual contrast ratio due to reflected light. Black walls, carpets and all.

More. . .

1. Aging eyes need more light, especially for low contrast tasks.

2. Aging eyes are more sensitive to glare.

3. Aging eyes function better with high contrast for many tasks, like reading.

4. Aging eyes need better lighting uniformity (but only if there is adequate contrast!).
   Peripheral vision may diminish.

5. Changing the eye's focus from one distance to another is more difficult.

6. Aging eyes respond well to reduced visual clutter and confusion.

7. As one ages, experiencing a more natural day/night cycle becomes increasingly important.
   
   In our opinion 2000:1 is fine for light controlled rooms and 400:1 for your family/living room or presentations.