Right angle prisms are used to deflect a light beam with 90 or 180°. Prisms are widely used in optical system, which can reflect, deviate and rotate beams of light as well as dispersing their wavelengths. Right angle prisms are used to deflect a light beam with 90 or 180°. Prisms are widely used in optical system, which can reflect, deviate and rotate beams of light as well as dispersing their wavelengths