Pilot Study: Measurement of Room Illuminance to Assess Automatic Brightness Control in Televisions

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Automatic brightness control (ABC) is an increasingly common feature found in new televisions (TVs) and computer monitors. ABC is intended to adjust TV screen brightness(luminance) according to the ambient light level (room illuminance). When implemented correctly, this can both reduce energy consumption and improve viewing quality. The current ENERGY STAR test procedure provides for a more favorable energy use rating for TVs with ABC, by measuring power consumption at two light levels (0 and 300 lux) and reporting a weighted-average energy use. However, this and other studies suggest that these levels are not representative of actual TV viewing conditions.As there were currently only limited data available concerning room illuminance, we undertook a small pilot study in 2011 to begin to answer two key questions: 1. To what extent do room illuminance levels vary depending on the location of measurement (e.g., center of the room, on the couch, or at the TV)? 2. What room illuminance conditions are prevalent when people watch TV? We measured room illuminance in the homes of nine volunteers in California and Colorado to begin addressing the above two questions. Although the study had the usual drawbacks of a pilot (limited sample size, time duration, etc.), it has, nonetheless, yielded useful results. The study shows definitively that there is large variability between measurements made at different locations in the room and, therefore, that location of room illuminance measurements is critical. Moreover, the majority (over 75%) of TV viewing occurred at illuminance levels of less than 50 lux (though measurements of up to several hundred lux were also recorded), a result that was consistent with subsequent larger-scale studies. This type of information can help determine how ABC-enabled TVs should be tested to best represent actual viewing conditions.

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