Take 2 identical laser pointers with new batteries of the same type. Turn them on and point 1 to sky, 1 to round. Leave them on and see how long the batteries last. (do this a few times so random variations cancel out). Measure for heat dumping, tie a thermometer to each of the laser pointers, and see which one gets warmer. if light is photon, 2 lasers should use same amount of power and dump same amount of heat. if light is gravitational wave, the laser point to sky will use less energy or dump more heat. how do you think?