Laser Demonstrator - for Light & Optics.                                                                                        Show some of the more curious aspects of optics. How? By focusing on its effects in water. Includes base for many light laser experiments. Very Popular. Light only moves at 75% its vacuum speed in water, which causes a ray to bend at the air/water interface, a phenomenon know as refraction. If the angle is steep, the ray will reflect off this interface instead. We use a low power laser beam and a circular tank filled with water to demonstrate refraction and reflection. As the tight, bright beam bends, its angle can be read on the scale printed around the tank. The laser is permanently fixed to the tank and can be pointed at any angle. Should you wish, you can fill the tank with mineral oil or other liquids to vary the effect.