Lightweight augmented reality (AR) eyeglasses have been increasingly integrated into human daily life for navigation, education, training, healthcare, digital twins, maintenance, and entertainment, just to name a few. To facilitate an all-day comfortable wearing, AR glasses must have a small formfactor and lightweight, while keeping a sufficiently high ambient contrast ratio especially under outdoor diffusive sunlight conditions, and low power consumption to sustain a long battery operation life. These demanding requirements pose significant challenges for present AR light engines due to the relatively low efficiency of the optical combiners. In this review paper, we focus on analyzing the power consumption of five commonly employed microdisplay light engines for AR glasses, including micro-LEDs, OLEDs, liquid-crystal-on-silicon, laser beam scanning, and digital light processing. Their perspectives and challenges are also discussed. Finally, adding a segmented smart dimmer in front of the AR glasses helps improve the ambient contrast ratio and reduce the power consumption significantly.