Measurement of automatic brightness control in televisions - critical for effective policy-making

摘要

Display luminance ("brightness") is the largest energy consuming function in televisions and monitors. Subjective research on televisions in households has shown that displays can be dimmed when room ambient light levels are naturally reduced, to achieve lower product power consumption while not diminishing the quality of the viewing experience. This energy-saving feature is most commonly called 'automatic brightness control' (ABC) and works by dimming the display's brightness in relation to the room illuminance. In Europe, manufacturers are given a small (5 %) power allowance when calculating the energy efficiency index for the energy label class, if the model has enabled and effective ABC under low light conditions. In the United States, the ENERGY STAR® program offers manufacturers a nominal allowance for ABC based on summing 25 % of the on-mode power requirement of the display at four nominal illuminance levels. The stark difference between the power allowances in these two leading economies is due in part to the lack of a good practicable test method and ability to characterize and quantify an optimum energy saving benefit of ABC. CLASP funded research to develop a novel and repeatable approach to the measurement of television power consumption and display luminance versus controlled ambient illumination under ABC control. This paper describes and illustrates the test setup and data logging equipment to capture the television's power consumption and screen luminance characteris- tics under a full range of ambient light levels, from <2 lux to >300 lux. This test method was applied to a small sample of televisions, and test results are provided. The test method provides insight into how the ABC algorithm is written in the television software, with some televisions progressively reducing screen brightness as the ambient lighting levels are lowered, and others simply having one large step reduction at a low level of room illumination. From an energy perspective, the software that progressively reduces screen brightness will achieve more energy savings. CLASP is submitting this test method to the IEC and CEN/ CENELEC for consideration as an update to relevant European and international test standards. Robust test methods like this one help policy-makers design more effective energy-efficiency policies and programs and can catalyse energy efficient design standardisation in the display manufacturing industry.