A periscope is a useful example of the law of reflection at work. It’s important that your mirrors are placed at a 45 angle, because light always reflects away from a mirror at the same angle that it hits it. In a periscope, light from an object strikes the top mirror at 45 and bounces off at the same angle. This sends light directly down the tube and onto the lower mirror. This mirror, also at a 45 angle, reflects light directly to your eye.