A multi-color LED is an electronic device incorporating light-emitting diodes of more than one color. Each light-emitting diode produces a different color of light by running electricity through a semiconductor, and the different colors are then blended together to create the desired final color. Most colors that can be perceived by the human eye can be produced in this way. Depending on their design, multi-color LEDs can produce light by combining two, three, or four primary colors; these configurations are respectively called dichromatic, trichromatic, and tetrachromatic. Multi-color LEDs are used in video display technology.
Like all light-emitting diodes, a multi-color LED produces light through a phenomenon called electroluminescence. When a light-emitting diode is switched on, electric current begins flowing through a semiconductor. As the high-energy electrons flowing through the conduction band of the semiconductor material transition to the material's lower-energy ground state, the energy they lose is emitted as photons. The energy level and wavelength of these photons depends on the material the semiconductor is made from, and the color of the resulting light depends on its wavelength.
Multi-color LEDs exploit the fact that when a person's eye is hit by multiple wavelengths of light from the same source, that person will experience it as a single blended color rather than perceiving the colors that correspond to the different wavelengths separately. For instance, the human eye perceives light with a wavelength of 620 to 750 nanometers as red and light with a wavelength of 495 to 570 nanometers as green. Both wavelengths simultaneously will cause a person to see yellow, which is normally produced by light in the 570 to 590 nanometer range. This makes it possible for multi-color LEDs to create the appearance of a wide array of colors.
The most common multi-color LED configuration, often called RGB, is trichromatic, with red, green, and blue diodes. These are considered the primary colors of normal human vision, reflecting the different wavelengths to which the three different types of cone cell in the human eye are most sensitive. Each pixel of an RGB LED display contains one diode of each of three these colors, which are so small and tightly packed together that the human eye cannot perceive them as distinct light sources. The diodes in each pixel switch on and off in different combinations as needed to produce all the colors seen by the viewer.
Multi-color LED displays are commonly used to create very large video displays, such as billboards and video screens at sports stadiums. Smaller television screens suitable for home viewing using multi-color LED technology exist, but lag behind formats such as plasma and liquid crystal display TVs in most respects. They should not be confused with LED-backlit LCD screens, which are often referred to as LED screens or monitors but are actually liquid crystal displays that use an LED for backlighting.