While they appear in many modern tech devices, LED lights actually date back more than 50 years. Originally an LED could light up in only one color, but modern variants can display up to six colors with shades in between. This can be particularly useful for conveying information in a tight space.
LED stands for light-emitting diode. It works using a semiconductor that is manipulated to have positively charged atoms, meaning there are spaces without electrons, known as electron holes. When an electrical charge passes through the semiconductor, the electron holes are filled. This results in the emission of photons, a form of energy that is visible as light.
The specific color we see in a lit LED depends on the level of energy involved. To control this energy level, manufacturers use different materials for the semiconductors. Each specific LED can display light in only one color. It took time for manufacturers to develop the use of different materials, so the range of colors supported by LEDs has widened over time.
Strictly speaking, an individual LED can't change color. Instead, a color-changing LED is made up of three separate LEDs in one casing, with a micro-controller operating them. The three LEDs are red, green and blue, so any of these colors can appear at a specific time simply by passing a current through one LED. Passing a current through two LEDs at a time produces the relevant combined color, specifically yellow, cyan or magenta. It's also possible to have different levels of current passing through the different LEDs, creating shades in between the six main colors. Passing current through all three LEDs at once creates a white light.
Uses of Color Changing
Color changing LEDs can be used for purely decorative effect, for example by slowly cycling through different colors. They are also useful as indicators in which a simple on/off display isn't sufficient, but space is limited. Google's Nexus smartphone range has a color changing LED that you can customize to show different colors for different alerts (such as email, text message or social media update) using dedicated apps.