Recent advances in augmented reality (AR) technology are attracting various emerging industrial and everyday life applications. However, resource limitations of mobile AR headsets, in particular, the energy constraint of battery-powered devices, can limit the scope of potential applications. In this work, we present LpGL, an OpenGL API compatible Low-power Graphics Library for energy efficient AR headset applications. We first characterize the power consumption patterns of a state-of-the-art mobile AR headset, Magic Leap One, and empirically show that its internal GPU is the most impactful and controllable energy consumer. Based on the preliminary studies, we design LpGL so that it uses the device's gaze/head orientation information and geometry data to infer user perception information, intercepts application-level graphics API calls, and employs frame rate control, mesh simplification, and culling techniques to enhance energy efficiency of AR headsets without detriment of user experience. Results from a comprehensive set of controlled in-lab experiments and an IRB-approved user study with 25 participants show that LpGL reduces up to 22% of total energy usage while adding only 46us of latency per object with close to no loss in subjective user experience.
