Design Of Contrast Ratio Measurement System With Adjustable Ambient Illuminance

With the development of display technology, it is a practical and systematic project to evaluate how well displays show the contents. Ambient Contrast Ratio factor considers the influence of ambient light on display panel in practical situation. This Ambient Contrast Ratio measurement system is based on VESA integrating sphere method and the available WRGB LED illumination method of Souththeast University, which can simulate the wide range of color gamut of ambient light intensity environment, besides the environment luminance can also be accurately adjusted, and the measurement process can be automatically carried out.First, this paper introduces the concept of Ambient Contrast Ratio and four Ambient Contrast Ratio measurement strategies, including fluorescent lamp illumination method, integrating sphere method, spectral radiometric method and WRGB LED illumination method. Advantages and disadvantages of these measurement methods are analyzed and a new design of Ambient Contrast Ratio measurement system is proposed. The new design achieves higher accuracy with a user-friendly interface. In the second part, the whole system structure is analyzed and a new matrix algorithms used for color light composition is proposed. In the third part, the design of the circuit board aiming at driving the LED light is elaborated. The drive circuit uses the PWM method. In the fourth part, the paper describes in detail the system's software design which is consisted of main module, luminance meter control module and PWM generating module. The main module is developed based on Matlab, implementing the matrix algorithms for color light composition and the user interface.After finishing the system, function tests and application tests are implemented. The results of function tests show that the system can precisely achieve the ambient light that users need, reaching an equivalent luminance up to 793cd/m2 when simulating the D65 illuminant environment. Throughout the gamut of the ambient light that can be achieved, the error of brightness is less than 3%, and the error of chromaticity coordinates is less than 2%. Application tests are divided into three groups, the first test system is designed to synthesize a wide gamut illuminant environment, and the ambient contrast ratio of iPad Air2 are measured in illuminant environments at both 6500K and 10000K. The second set of tests measure the ambient contrast ratio of monitors which share a similar contrast rate but have quite different actual display performances. An AOC LCD monitor and an iPad Air2 were tested at 6500K color temperature to compare their ambient contrast ratio. The third set of tests measure the ambient contrast ratio of self-luminous display devices and reflective type display devices in contrast. Ambient contrast ratio of a Kindle e-book is measured on the system. Test results show that the system can accurately measure the ambient contrast ratio under various ambient light conditions of different types of displays, the parameters obtained can reliably represent the display effect in practice.