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If you’re looking to project images onto a wall, instinct says you’ll need a white wall. After all, projector screens are white. But is that the case, or will a projector work on grey or black walls?
A projector will work on grey or black walls, particularly if there’s ambient light in the viewing area. The more ambient light in the room, the higher the light output you’ll need from your projector. You may also need to increase the reflectivity of your wall to maintain image brightness.
It seems counter-intuitive to use a projector on colored walls. Yet, the wide availability of both grey and black projection screens suggests it’s possible. Before you whip out the paintbrush, read this primer to help you achieve the best results.
Read my article on the best types and colors for projector screen paint.
Why Use a Projector on Colored Walls?
To understand why you might want to use a colored wall, let’s look at the issues that arise with white projection surfaces.
Using a Projector on White Walls
If you remember those white screens, you’ll also recall closing curtains and turning off lights before viewing.
And that’s the issue with white screens. They’ll work well if you can black-out your room.
It’s all down to the way a projector works.
Understanding How a Projector Works
A projector projects light onto the viewing surface. The image you see is from the light reflected off that surface to your eyes.
The projector uses red, green, and blue light in various combinations to create the colors you see.
For example, to display a red color, the projector emits red light but blocks the other colors. White is all the colors transmitted at the same time.
Black is different because black means there’s no light. So, the black on the screen is really an area of no illumination.
Using a White Screen in a Blacked-Out Room
The black you see on your screen will only be as black as the screen is under the available light conditions.
You can see this in practice with a simple experiment. Take a white piece of paper into a blacked-out room. It’ll look black. And that’s the best representation of black that you’ll see under black-out conditions when you run your projector.
Because the black is dark, it provides contrast with other colors, so they appear bright.
Using a White Screen in Ambient Light
Let’s get back to the experiment. Add some ambient light to your previously blacked-out room. You’ll see that the white paper appears more grey than black. With ambient light, that greyish color is the best representation of black that you’ll see from your projector.
That’s because the white paper is reflecting the ambient light source, diluting the color you see. Instead of black, it becomes grey.
The effect is the same on other colors, which become diluted or washed out by the ambient light.
It’s due to a reduction in contrast. The additional light from the ambient source makes what you see brighter, but it reduces contrast.
So, if you can’t or don’t want to eliminate ambient light in your viewing area, grey or black screens may help.
Using a Projector on Grey Walls
Now, repeat the above experiment with a grey piece of paper. You’ll see that the grey paper looks much darker than the white did when you introduce ambient light.
A colored surface absorbs ambient light. So, with a grey surface, even when there’s ambient light, there’ll be more contrast between the dark areas and the lighter surrounding areas.
But, of course, the grey surface impacts the other colors in the image as well. The effect is to give a grey tone to white areas and what should be bright colors, reducing their vibrance.
Using a Projector on Black Walls
The black surface just takes the concepts that apply to grey surfaces a step further.
By making the projection surface black, you improve the black level even more than on a grey surface.
The black screen absorbs more ambient light. So, it’ll display darker blacks better than a grey screen when you start increasing the ambient light level.
Because the blackness is enhanced more, it amplifies the contrast between the black areas and other colors. A black screen can avoid some, but not all, of the dulling of colors that a grey screen produces.
In general, the more ambient light you have, the darker the projection surface you may need.
This video puts white, grey, and black screens side-by-side to show how they perform under different lighting conditions. It’s based on a particular type of painted surface but is a useful guide to what might be achievable.
But, things are never quite as simple. Various factors determine whether the wall you want to use will produce good results.
What to Consider When Using a Projector on Grey or Black Walls
If you already have a grey or black painted wall that you want to use, try it out. If it gives you the desired image quality in the lighting conditions you want, you’re ready to go.
Otherwise, to project onto grey or black walls you should consider the following in addition to ambient light levels:
- the amount of light your projector emits, plus the distance from and size of your screen area
- the amount of light your wall reflects.
How Much Light Does Your Projector Emit?
The amount of light emitted by a projector is measured in lumens. Higher lumens means more light and a brighter picture.
The lumens you need depends partly on your screen size and the distance between it and your projector.
If you’re using a darker surface, which absorbs light, you’ll need more lumens to compensate for that. Otherwise, you’ll lose some brightness.
How Much Light Does Your Wall Reflect?
Reflection from your wall is another factor influencing the image you’ll see.
The degree to which it reflects light is referred to as the gain. The gain is a ratio.
A gain of 1.0 means the light reflected off the surface to the viewer equals the light coming from the projector. You might expect a white screen to have a gain of around 1.0, or even 1.4.
In contrast, a negative gain, say 0.5, means the surface reflects less light to the viewer than it’s receiving from the projector. So, 0.5 gain means it reflects half the light. This is what you’d expect from a darker surface.
With a darker surface, you’ll get good blacks, but other colors may lack brightness.
You could invest in a higher lumen projector to overcome this. Or, you can increase the gain of your surface with special paint designed for use with projectors.
For example, Paint On Screen Projector Screen Paint (Amazon link) says it gives your surface a gain of 2.0. That suggests you could use it with a modest lumen projector because it will reflect twice the amount of light coming from your projector.
Or, you can fix material designed for use as a screen to your wall. This
Ambient Light Rejecting Projector Screen Material (Amazon link) is the type of thing you’d be looking at.
You can see similar materials of different colors in this video. It demonstrates how each performs under various light conditions.
As you can see, it’s possible to use grey or black walls as a projection surface.
But you’ll need to consider:
- the ambient lighting in your viewing room
- your projector’s lumen level
- the screen size and distance from your projector
- your wall’s gain
Play around with different combinations of these elements to get the right image quality for your circumstances. With the equipment and materials out there, you’re bound to find a combination that works for you.
Also read : Projection on screen vs a wall – key differences