Do You Waste Laptop Battery to Light the Room

Most widely used timeout based DPM (display power management) only turns off the display after there has been no user input for a fixed time. There have been a couple of studies (e.g. FaceOff) that try to save more energy by detecting user presence. However, the purpose of a display device is not to light the room, but to provide the graphical view to the user. Thus, the display does not need to be turned on, even when the user is present but not gazing at the display. In this article, we propose a power management scheme that uses a web cam to determine if the user is actually gazing at the display. In our evaluation result, the conventional DPMs turn off the display for 30~40% of the total time by detecting the state where user is not present. However, our proposed scheme turns off the display for nearly 50% of the total time by additionally detecting the state where the user is not gazing at the laptop. Our proposed scheme reduces average system-wide energy by 5% and 4% (up to 13%), compared to the timeout based DPM and FaceOff, respectively, with acceptable amount (0.8 per hour) of user irritation.