If you're a big-time movie fan, do you ever wonder if watching all those movies in the dark is good for your eyes? This article takes a look at how the human eye reacts to light and pictures. Televisions.com hopes to bestow some handy tips upon you along the way, to make sure you are doing the best for your eyes. After all, you only get one pair.

The iris adjusts to let the right amount of light into the eye. The problems begin when this system gets confused.

In a movie theater, all the lights are turned off, yet at home we are warned from a young age against doing exactly that. What is the difference, and what other important factors need to be considered?

For those looking for a bit of background, we begin here with an introduction to how the human eye perceives light. Then, from a more practical point of view, we'll run through a few crucial aspects for optimizing the lighting for your own TV viewing.

We all know the effect from visiting the movie theater in the afternoon. You come outside afterwards and you're blinded by the daylight. Your eyes need some time to adjust, since the picture on a movie screen is not as bright as the light outside. In fact, we could play back movies with even less than the standardized 16 footlamberts of brightness. However, if the picture is too dark, it will actually lose sharpness.

When the eye is in a dark environment, the iris opens wider to allow in more light. The problem is that it allows in more light from the sides, and therefore more scattered light, giving a less accurate picture on the retina. A bright screen, on the other hand, gives a crisper, more contrast-rich image.

Too much light, however, is also not ideal. The standard for work terminal displays in studios, for example, is between 100 and 120 cd/m2, which is just a fraction of that seen on today's monitors and TV screens. The reason for this voluntary limiting is simple: The eye should not have to adjust itself if you look away from the screen to an object in the room, for example to look a piece of paper.

Besides the iris, it is also a question of the eye's receptors, that is, the light-sensitive cells on the retina. These can take relatively long to adjust, for example when driving into a tunnel or back out the other side. So, the important factor is the change of lighting. Therefore, large differences in illumination should be avoided for the eye's sake.

Factors to be considered

So far, only Philips has come up with an optimal solution. Its "Ambilight" technology uses fluorescent bulbs - and more recently LEDs - around the picture's frame to cast a soft, diffuse light onto the wall behind the set. This reduces the brightness difference between the picture and its surroundings.

Perfect: Ambient illumination should come from behind the screen, as seen here with this "Ambilight" TV from Philips. Philips also offers a stand-alone version of the system, known as "Living Colors".

Putting a lamp on the audience's side of the picture is totally wrong. The light from any lamps would then reflect off the screen, effectively doing more harm than good. It is crucial that the lighting does not fall directly on either the viewers or the screen.

Illumination in the room will harm the picture's contrast, since the blacks will no longer be as black. On the other hand, if there is too little ambient light, differences between the black levels on good and bad sets will become more obvious.

Tip: If needs be, use a small light to illuminate the floor or the ceiling, so long as nothing there will reflect the light back to you.

The eye will get used to more than just the level of brightness. The color temperature, or the exact color mix displayed for white, is another important factor. The brain will subconsciously record a sort of "white balance", as a camera does, using various objects that usually have a neutral color temperature: for example a piece of paper or a wall. So, if you put a "warm" lamp (with a large red component) next to the TV, this will make the picture look "cold" (a large blue component), and vice versa.

LCD displays often have a cold color temperature and therefore look more pleasant under "cold" light sources, such as fluorescent tubes, which make the TV picture look warmer. Or, a plasma TV with a rather tepid picture can be made to look clearer with a warm light. The best scenario, of course, is to have a well balanced screen with neutral ambient light (near to the ideal color temperature of 6,500 Kelvin).

Red sky at night: Getting the correct color temperature is central to a sunset's allure.

Typical flat-panel displays with diagonals of around 40 inches (102 cm) are simply too small to keep the human eye fully occupied.

At the same time, the screen is also often way too bright, causing a slight "burn-in" effect on the retina, whereby you can still see a glow from the TV screen when you close your eyes. One way of relieving this effect is to increase the ambient lighting, as seen with the "Ambilight" technology from Philips. But, it is better to tackle the root of the problem: The picture is just too small.

The picture in the movie theater fills around thirty degrees of the field of vision. This corresponds to the so-called "central field of vision", in which the human eye sees images sharply, as opposed to the "peripheral field of vision", which is blurrier but more sensitive to motion. Since the picture fills the central field, the eye is not distracted by other objects, as it was with the small TV screen, and can correctly adjust to the brightness of the picture. This situation therefore needs no ambient lighting, which could actually be counterproductive.

This is therefore what you should aim for in your living room or home-theater. We often talk about a rule of thumb that states: Ideal viewing distance = 2 x the width of the image. If you follow this rule, the picture fills your central field of vision, and the subconscious is better able to lock onto the action in the movie.

Only with a big screen like this can you afford to sit several meters away from the picture. Otherwise, the eye will not be able to adjust properly.

Ultimately, there are arguments supporting both sides to the dilemma: Should I watch TV in the dark? However, this is only the case if you haven't properly addressed certain other factors. If your screen is big enough, and its colors are properly adjusted, the answer to the question becomes a clear "yes". But, not everyone has a big enough screen for this, and the cinema-purist's motto applies: You will only need ambient lighting if the screen is too small.