Factors affecting the contrast of LED display

　　In order to make the contrast test meaningful and repeatable, it is necessary to prepare a completely dark dark room to eliminate the interference of external light. In contrast test, LED module, test instrument and light source are the three key factors of interaction. Most LED display manufacturers can only do a basic on off test process, and its off state corresponds to the video black field. However, there is no uniform test technology standard in the whole industry. Although there are some statutory standards for measuring contrast for some display technology, such as VESA FPDM (Video Electronics Standards Association Flat Panel Display Testing), this is not fully applicable to the LED industry. Different from flat panel display measurement, environmental light source (sun) and measuring tools (viewer) are changing every day and every moment, while pedestrians driving or walking are also changing every minute, which is difficult to repeat in the test and explain clearly in a product manual.

　　Outdoor LED display

　　It should also be noted that under the test conditions, compared with the large size of the complete LED display screen, only a single module or a collection of modules can be tested.

　　In the measured environment, the ambient light is used to reproduce the real outdoor viewing environment. Obviously, the test results will be greatly affected by adjusting the light source brightness (unit: lux) in the test environment, which can be used to enhance the advantages of product promotion. Since the sunlight on the surface of the display screen is changeable, any result can be considered reasonable.

　　At present, the ambient light brightness range used in the instructions issued by the display screen manufacturer is 40-50,000 lux.

　　The contrast test result can also be improved by adjusting the angle of the light source relative to the display screen module. As mentioned above, the LED module will have horizontal shutters, that is, sun shades, distributed between each row of LED or each row of pixel points. Increasing the angle of light source relative to the LED can create a larger shadow area on the surface of the module, thus ultimately improving the black field state of the display screen.

　　Finally, the display manufacturer can adjust the angle of the test instrument relative to the display surface to facilitate their own control of the final contrast parameters. It should be noted again that this may also be the result of the interaction between the light source and the horizontal sun visor.

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