Right-angle prisms were named for their classic 45˚-45˚-90˚ triangle shape. This unique geometry is a key reason why they are the most common and versatile prisms used in experimental physics today. While they have a variety of applications, right-angle prisms are most commonly used as a convenient and cost-effective way to change the direction of a beam of light. Depending upon the direction at which incident light rays enter the prism, their path can be rotated by 45, 90, or 180 degrees. As a result, right-angle prisms are often a component of a variety of optical devices, such as in periscopes and microscopes.