How to Evaluate the Brightness, Contrast, and Viewing Angle of a Liquid Crystal Display Module?

The brightness, contrast, and viewing angle of a liquid crystal display module should be measured separately under uniform environment, signal, and instrument conditions. Brightness is evaluated by the luminous intensity and uniformity of the white field; contrast is evaluated by the ratio of white-field brightness to black-field brightness; viewing angle is evaluated by the angular range within which contrast, color, and grayscale still meet requirements in different viewing directions. Jinpeng recommends evaluating the three indicators jointly, rather than judging display performance based solely on a single nominal value in the specification sheet.

How to Measure the Brightness of a Liquid Crystal Display Module?

The brightness of a liquid crystal display module is the luminous intensity emitted by the screen in a specified direction, usually expressed in candela per square meter (cd/m², also called nit). According to IEC 61747-30-1:2012 "Liquid crystal display devices — Measuring methods for transmissive liquid crystal display modules", brightness measurement should define the test image, measurement direction, instrument position, and environmental conditions to ensure reproducible results.

During testing, allow the LCD module to warm up for about 30 minutes, then display an all-white image and align the luminance meter perpendicular to the center of the screen. The instrument should use a spectral response that matches the human eye's visual response; if evaluating white color temperature, refer to CIE 15:2018 "Colorimetry", in which the correlated color temperature of standard illuminant D65 is approximately 6504 K.

Brightness should not be measured only at the center point. For engineering acceptance, the 5-point method (center plus four corners) or a 9-point layout in a 3×3 grid can be used, and the brightness uniformity is calculated as: minimum point brightness ÷ maximum point brightness × 100%. For example, if the maximum point is 500 cd/m² and the minimum point is 400 cd/m², the uniformity is 80%; this figure is only a calculation example, and the actual results and limits shall be based on the product specification and the technical agreement between both parties.

How to Evaluate the Contrast of a Liquid Crystal Display Module?

The contrast of a liquid crystal display module is the ratio of white-field brightness to black-field brightness under the same test conditions, calculated as "white-field brightness ÷ black-field brightness". For example, if the white field is 500 cd/m² and the black field is 0.5 cd/m², the static contrast ratio is 1000:1; the data is only used to illustrate the algorithm and does not represent the performance of a specific Jinpeng model.

According to the International Committee for Display Metrology (ICDM) "Information Display Measurements Standard, IDMS 1.1", display measurements need to record the test pattern, viewing geometry, ambient illumination, and equipment status. This means that darkroom contrast and ambient-light contrast cannot be directly mixed, because reflections on the screen surface raise black-field brightness and reduce the light-dark gradation in actual viewing.

During the specific test, the white field and black field should be displayed sequentially under the same backlight, temperature, input signal, and measurement position. In addition to the full-screen static contrast ratio, a checkerboard pattern can be added to check the performance when bright and dark areas appear simultaneously; the test report should specify the instrument model, warm-up time, ambient illumination, and measurement distance. Refer to IEC 61747-30-1 and IDMS for the relevant methods.

How to Determine the Viewing Angle of a Liquid Crystal Display Module?

The viewing angle of a liquid crystal display module is the angular range within which the image still meets the established contrast, color difference, or grayscale requirements after the observer deviates from the screen normal. During evaluation, measurements should be made by rotating in four directions: horizontal left/right and vertical up/down. It should also be stated whether the angle is a unilateral value or the total of both sides, to avoid confusing "80° left and right respectively" with "160° total horizontal range".

Industry testing often uses a contrast ratio of not less than 10:1 as a threshold for defining the viewing range, but this value is not suitable for all applications; the final decision should be based on the product technical specifications. According to the measurement approach of the IEC 61747 series standards, color shift, grayscale inversion, and brightness attenuation caused by viewing angle changes should also be observed, because reaching 10:1 does not necessarily mean that the colors of the picture still meet the requirements for use.

For instruments, industrial control, or fixed-position equipment, Jinpeng recommends first confirming the actual viewing direction and then determining the viewing angle specification of the LCD module. For example, if the operator mainly views from below, the downward viewing angle should be verified as a priority, rather than only comparing the total horizontal angle; outdoor projects should also include ambient-light testing. The final data for brightness, contrast, and viewing angle should all be based on the specific sample, the agreed method, and the test report.

References

IEC 61747-30-1:2012, "Measuring methods for transmissive liquid crystal display modules".
ICDM, Information Display Measurements Standard (IDMS 1.1), 2012.
CIE 15:2018, Colorimetry.