How do I test the brightness of an LCD display?

LCDs are internally analog devices like CRTs, where an analog signal and circuitry control the brightness of each pixel. However, LCDs have digitally addressed pixels, behave quite differently from CRTs, and require a different evaluation approach.

Brightness

When selling electronic products like LCD screens or monitors, some parameters are essential to consider, such as backlighting, colors, brightness, and backlight control. However, brightness is the most important parameter when it comes to customer satisfaction and free reviews. The brightness of LCD screens ranges from 250 units to over 1000 units, with light output being about 350 to 450 candelas (cd) per square meter. The brightness or luminance of a screen is crucial in determining which LCD screens need replacement, repair, or are irreparably damaged. LCD screens can also help distinguish different models based on their luminescence and viewing angle.

Candlestick

One way is to buy a photometer that measures brightness in candelas per square meter (cd/m^2). Then, turn off the lights in the room, blocking any outside light. The LCD screen must remain on. Next, maximize the brightness of the LCD. The LCD's background screen must somehow become completely white to get a standard display. Either enlarge a blank document or open a Word document to achieve the desired results. The next step is to place the area of the photometer's sensor on the screen and take a measurement according to the instructions provided with the photometer. Placing the photometer on the screen ensures observation of maximum intensity and standardizes the measurement process between screens. Measuring from the usual position of computer users introduces too many variables, distorting the one authentic reading. Placing the sensor on the white screen is especially important if the desired result is a standard measurement. It may be useful to take some measurements from different angles, especially if one wants to limit the observable area. For example, all readings could be taken at a 30-degree angle to the screen to standardize the measurement. For precision, it might be advisable to have a protractor nearby.

Methods

Computer experts recommend different types of tests, including hardware and software tests. By applying the trichromatic filter method, the luminance colorimeter can measure brightness, color temperatures like CIELAB, CIELUV, and color differences. The four measurement angles can also be switched. It is suitable for luminescence measurement in the low brightness range, which requires a small measurement angle, e.g., 0.1°/0.2°. For remote measurement, the extension line is used for both the main engine and the inductor.

Input color coefficient and brightness deviation are some of the functions that can be achieved with an additional instrument keyboard. Luminance colorimeters also prove useful in computers for analysis and printing, lighting technology, film, television, data storage, architecture, and other fields.

The software "Monitors Matter Check Screen" is a professional method for testing LCD brightness software, which not only detects industrial LCD screens, but this software also tests CRT (cathode ray tube) displays. Due to the numerous functions installed in it, this software can also detect the color of the LCD, the text display effect, response time, bad spots, and other important indicators.

Displaymate Multimedia

For LCDs, creating dark gray and black colors is quite difficult. Therefore, the black level of an optimally adjusted LCD should be quite close to absolute black, unless the LCD is placed in dimly lit environments. DisplayMate offers a visual black level test for such authentication. The brightness level of the LCD should be adjusted from minimum to maximum to evaluate the black level of the LCD.

Positive or negative shadows, known as banding, often appear visibly on the right side of the screen. However, severe banding obscures image details in front of it. Image distortion is most noticeable in high-contrast situations, and LCDs show a tendency towards both horizontal and vertical banding.

The video bandwidth index is used to measure the visibility of high-frequency details in an image. A result of 100 is perfect and signals that both high and low frequencies are produced identically. LCDs that use a digital input should also have such an output. For analog LCDs, however, a result with a value of 100 is not possible, and values below 100 are considered second-level performance. To achieve optimal results, it is essential to perform this test on a green background. Values closer to or above 100 indicate either overheating or compensation, which is considered a serious performance deficiency in overall LCD performance.

The video bandwidth index for the three primary colors red, green, and blue should be equal. However, suppose a color shift from large to small details is observed in an image. In that case, the video bandwidth index in its three primary colors cannot be identical and must therefore be abnormal.

Colors

If the intensity of the three primary colors does not change uniformly with the signal level, grayscale colors will be displayed upon closer inspection, coloring one or more points on the LCD screen. Due to the unbalanced saturation between the RGB channels, the tint is usually visible near black at low or maximum intensity.

LCDs are not designed to produce a smooth grayscale with 256 discrete intensity levels, increasing from black to peak white. Using "Intensity Level Ramp" and "Intensity Level Color Ramp" can evaluate the smoothness of the grayscale. Look for jumps, skips, flat spots, bumps, waves, dips, or other irregularities that stand out from the smoothness of the grayscale.

For a portable monitor for a laptop, the best way to test a laptop screen is to repeatedly adjust the screen brightness from lowest to highest, preferably on a white background. Then, slide the laptop screen from the farthest to the closest point and vice versa, checking for screen flickering.