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Light-emitting diodes (LEDs) come in a variety of colors and brightness. As electric current passes through the semiconductor crystalline structure, some of the electric current is converted to photons, and light is emitted. Color-changing LEDs combine three different-colored LEDs into a single, two-lead package. When current is applied, the colors cycle through the three different colors and then a combination of colors.
A color-changing LED has a control circuit built into the LED package. The control circuit governs which of the three separate light-emitting diodes within the package are lit at any given time. Some control circuits can vary the intensity of the light for each LED, making the entire visible spectrum of colors available from the color-changing LED package.
The leads from an LED go inside a plastic case and support a semiconductor crystal called a die. The die is the actual light-emitting diode, and its composition governs the wavelength of light that the LED will emit. LED die composition usually includes gallium and arsenic, but other materials such as aluminum, phosphorus, indium and zinc provide a variety of colors. The dies of a color-changing LED incorporate these different materials to create the range of colors.
A color-changing LED differs from a multi-color LED in several ways. The multi-color LED uses two or more dies of different colors, but it lacks a control circuit to control the dies within the package. Instead, the package has multiple leads, and each individual die within the package is turned on and off by supplying power to just that die. For example, a tri-color LED will have four leads: one to supply power to each of the three LEDs and a fourth common lead.
A multi-color LED lacks a control circuit, so a separate means of controlling the colors is required. A simple circuit might turn on just one color at a time for various purposes, and a more complex circuit can combine colors. This allows for greater control over exactly what color is displayed by the LED package. The color-changing LED offers no such control at all. The frequency of the color changes, and the order of the colors is fixed and cannot be changed.
The end user cannot control the color changes or the frequency of the color changes, so a color-changing LED is primarily used in novelty lights, decorations such as color-changing LED holiday lights and other such uses. Use of the color-changing LED is likely to remain in its niche as a novelty or decorative light, and the multi-color LED is likely to continue serving its existing market.