Color wheel (optics)
A color wheel or other switch for changing a projected hue is a device that uses different optics filters or color gels within a light beam. Common usage includes continuously-rotating wheels for seasonal home displays and controllable color wheels for a particular instrument, while non-wheel devices include scrollers and semaphore types with lever arms.
In projectors
A common application of the color wheel is to provide a color filter for a single-chip projector, which would otherwise only be able to display a greyscale image. The color wheel is placed in front of the light source and spins rapidly, splitting the light into red, green, and blue primary colors. The chip then displays each primary color one at a time, quickly enough that the human eye will see them as a full-color image. This method is not perfect; in high-contrast scenes, such as a bright streetlight against a night sky, or the credits at the end of a film, the individual color frames may be visible; therefore, high-end and professional projectors split the light with a prism and use three separate chips, one for each primary color.