Our Picture Quality Tests

Brightness

The main component of our brightness testing is the White Light Output test. The primary goal of this test is to determine how much light a projector emits. The two examples below show the difference between a projector with low brightness (left) and one with high brightness (right). The VANKYO Leisure 3 is incredibly dim—so dim that it's hard to even tell that the projected image is supposed to be white. The Epson Home Cinema 3800 looks much better overall and is bright enough to overcome some ambient light.

VANKYO Leisure 3 - 41 lm

Brightness Uniformity - 45%

Epson Home Cinema 3800 - 2,287 lm

Brightness Uniformity - 94%

To run the test, we set up the projector in our completely black, light-controlled room. We connect the projector to a computer, which we then use to display a full white screen. We measure the luminance of each section using a Konica Minolta T-10A illuminance meter. We then take a picture of the screen, and an overlay is added to show the brightness of each section.

These nine measurements are great, but they represent spot readings over nine points, not the total light output from the projector. To arrive at a final measurement, we take the average of the nine boxes to determine the average light output and multiply it by the screen area to arrive at the final white light output number in lumens. As part of this, we also need to apply a geometric correction to account for the measuring distance between the T-10A illuminance meter and the screen.

An example of a DLP color wheel (source: projectorjunkies.com)

The peak brightness measurements with white slides are great, but nobody watches white slides, so how does this represent real usage? That's where the Color Light Output test comes into play. Instead of measuring pure white, this test aims to see how bright colors are.

In a perfect world, colors would be just as bright as pure white, but this isn't always the case, depending on the projector technology used. Regardless of the light source, three-chip projectors use separate channels for red, green, and blue, so for those projectors, white is simply the three channels combined, and pure white brightness is the same as the color output.
Single-chip DLP projectors, however, usually use color wheels like the one shown here to display each channel. Color wheels used to just consist of separate red, green, and blue channels that were used to make any color as well as pure white.

Manufacturers started adding white sections to some of these wheels, though, as a way to increase the overall peak brightness and deliver brighter whites. Projectors with a white section on the color wheel don't combine red, green, and blue to produce pure white; white is usually significantly brighter than the peak color output, as it's just the light from the lamp shining straight through. This results in dimmer colors, as colors on these projectors are produced by shining light through an imperfect color filter. This effect is so significant that on some projectors, colors are up to 60% dimmer than pure white.

To test the color light output, we use the same setup as the white output, but instead of measuring pure white, we use the three different test images shown above. We measure the brightness of all nine rectangles in all three slides for a total of 27 measurements. We then add up the brightness measurements from each rectangle across the three slides and take the average.

Taking the white light output numbers as a starting point, there's another interesting test we can run: brightness uniformity. As the name suggests, this test looks at the measurements we took in the previous test to see how uniform the brightness is. After all, we don't want a brighter screen in the center than on the edges. Looking at the same two projectors from above, the VANKYO Leisure 3 has very poor brightness uniformity, and you can clearly see it as the sides of the projected image are significantly darker than the center. On the other hand, the Epson Home Cinema 3800 is very uniform. There's some variation in lux around the corners, but it's not noticeable.

VANKYO Leisure 3 - 41 lm

Brightness Uniformity - 45%

Epson Home Cinema 3800 - 2,287 lm

Brightness Uniformity - 94%

So, how do we actually calculate the uniformity? Turns out, it's really simple. We take the average of the four corner boxes and divide that number by the center. There are multiple ways we could do this, and different manufacturers use different methods to arrive at their own numbers, but this is one of the most commonly used methods.

While running the White Light Output test, we also use a Konica Minolta LS-100 luminance meter to measure the brightness of each square in cd/m², or nits. We take the average of those measurements and add it to the review. We do this simple test to give you a rough idea of how bright a projector is relative to a TV. When comparing these numbers, though, it's important to remember that the perceived brightness of a display, regardless of type, is relative to the size of the screen. A 100" projector screen at 200 nits will look brighter than a 55" TV of the same brightness at the same viewing distance.