A light projecting system comprises: a waveguide comprising a first surface, a second surface, and a fourth surface, at least one of the first surface or the second surface comprising a first plurality of grating structures; a light source coupling light into the waveguide to form an in-coupled light beam, wherein: each of the first grating structures is configured to disrupt the total internal reflection to cause at least a portion of the in-coupled light beam to couple out of the waveguide, and a remainder beam of the in-coupled light beam undergoing the total internal reflection being coupled out of the waveguide after the out-coupling at each of the first grating structures; a detector configured to receive and measure the remainder beam; and a processor coupled to the detector and configured to determine if a dangerous condition occurs based on the measured remainder beam.