What is light pollution and how can it be eliminated?


Many people install their home theater in the living room. Unlike a movie theater, the living room is not always ideal for achieving good image quality. “Why?” you might ask. Because of light pollution.

What is light pollution? How does it appear on a TV or projector? How can you reduce sources of light pollution? Here are some answers.

Light pollution with a TV

With a TV, it is mainly reflections on the screen that alter the legibility of images. During the day, the television can behave like a mirror if it does not have an effective anti-reflection filter. Even when you turn the brightness setting to the maximum.

Reflections on a TV
A TV can behave like a mirror in broad daylight, especially when there is a window nearby. In this case, reflections can be very annoying.

The solution is to make the room dark. For example, you can install blackout curtains on the windows.

Do you like ambient lighting when watching TV? Be careful where you place your lights. If they are in the axis of the screen behind the viewers, they will be reflected! The same goes for reflective objects placed behind the spectators and indirectly illuminated ( glass cabinet, decorative frame, mirror…).

Reflections of ambient lights on a TV
When badly positioned, ambient lighting can generate light pollution on the screen. Here, the floor lamp placed at the back of the room, behind the viewers, is reflected on the screen. There is also the reflection of a computer screen.

Philips Ambilight TVs offer an ideal solution for those who want to maintain ambient lighting while watching TV. They have several LED strips behind the screen that emit colored light. This halo can even be matched in real time to the image displayed on the screen, to enhance visual impact!

Philips Ambilight TV

Light pollution in video projection

In video projection, the primary source of light pollution is ambient light. Try to project in a bright room: the image is dull, the contrast very weak. Daylight (or lighting) reflects off the projection screen, drastically reducing contrast. Unless you have a very bright projector (3000 lumens or more), or a technical screen capable of limiting reflections, projection conditions will most often be catastrophic.

Dull image in projection due to ambient light
Even in a room with dark walls, ambient light impairs the quality of the projected image, especially if a standard white canvas is used.

The simplest solution is to make the room dark, by closing the shutters and/or the curtains.

Darkness improves contrast and color rendering
In the dark, the projected image is more contrasted, the colors more vivid.

The color of the ceiling and the walls also impacts the quality of the image. Why?

Because the ambient light as well as that projected by the projector is reflected on the walls and the ceiling. If they are white or light in color, the reflections are greater and the projected image suffers. The colors appear washed out, the contrast is poor: the image is disappointing. Windows and bay windows pose the same problem.

Projection in a room with white walls
In a bright room with white walls, the projected image is dull: the contrast is weak and the colors lack vibrancy.

There are several solutions to these problems. First, you can paint the walls and the ceiling. Ideally a dark color, with matt paint to limit if not eliminate reflections. It is not necessary to paint the whole room! You can start with the wall behind the screen. If necessary, the ceiling and side walls located between the screen and the viewers can also be painted. This creates a sort of darker alcove around the screen. The image regains greater dynamic range with better contrast. Bright, well saturated colors are achieved.

If you do not want to darken the walls, you can use dark colored curtains. They can be installed on the sides of the spectators, and also on each side of the screen. The curtains also help eliminate glare on the windows. Simply draw them before the movie to improve the contrast and colors of the image.

Should you buy a technical screen for projection?

Some projection screens use a technical canvas capable of attenuating reflections and improving the contrast of the projected images.

High-contrast gray screens are particularly suitable for video projection in a living room with light walls. They are also recommended for 3D movies. Their high reflective potential compensates for light pollution, but also for the drop in image brightness when using 3D glasses.

Projection on a white wall in a bright room
In a very bright room, the image projected on a white wall (here with an ultra short throw projector) is far from ideal.

There are also specific screens for ultra short throw projectors. An example is the Lumene Movie Palace UHD 4K Extra Bright. This canvas has a layer shaped like a microscopic saw-tooth. This layer reflects the beam of light from the projector in the axis of the screen, towards the spectators. Ambient light, especially that reflected by the ceiling, is reflected outside this axis. These screens are most often referred to as ALR (Ambient Light Rejecting) screens. They are sometimes called CLR (Ceiling Light Rejecting) screens.

Projection on a technical screen in a bright room
With an ultra-short-throw projection screen equipped with a technical material, the image is more contrasted and the colors more vivid, even in daylight.

Unexpected sources of light pollution…

Finally, other sources of light pollution exist that we don’t automatically consider. For example, there is the finish of the speakers, the speaker stands and the furniture. It is therefore advisable to avoid clear or reflective surfaces such as lacquered finishes, as well as glass shelves. It is best to opt for dark and matte finishes.

Reflections and light pollution with lacquered white furniture
A white lacquered piece of furniture is not ideal, neither with a television, nor with a video projector (here an ultra short throw projector). It draws attention and generates white reflections under the screen.

To conclude

We often forget it, but seeking to eliminate the various sources of light pollution can greatly optimize image quality. Whether using a television or a video projector, it significantly improves the contrast of the image. This also helps to increase its dynamic range. This is essential to fully enjoy films, series and video games in HDR. In doing so, colors are also improved, which are then more vivid and saturated. This produces a much more pleasant and realistic image.

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