As we mentioned before, LED stands for light emitting diode. This type of lighting is completely different than the other types of lighting we have discussed so far. They do not need specific gases, filaments or moving parts because they are made from semiconducting materials, which makes and LED a semi-conducting device that produces light. The underlying principles of an LED light are the opposite function of a photovoltaic system. An LED semiconductor chip form an junction between and n-type and p-type semiconductor materials. N-type materials pass charge using electrons, and p-types pass charge using holes. See the figure below for a description of the circuit.
LEDs do not directly produce white light. Due to this quirk, LEDs were originally used for colored light applications such as traffic lights and exit signs.
Because of their extremely high efficiencies (150 lumens per watt!!, and up to 90 % more efficient than incandescent light bulbs), researchers found ways to convert their outputs to white light. As such, they are one of the highest efficiency lighting options available.
Here are three examples:
- Phosphor conversion, in which a phosphor is used on or near the LED to convert the colored light to white light
- Color-mixed systems, in which light from multiple monochromatic LEDs (e.g., red, green, and blue) is mixed, resulting in white light
- A hybrid method, which uses both phosphor-converted (PC) and monochromatic LEDs.
Methods of making white light from LEDs.
The image is a diagram titled "Creating White Light," showcasing three methods for generating white light using LEDs. Each method is illustrated with a schematic on a gray background.
- The first representation is labeled "Phosphor-Converted LED." It includes a large arrow labeled "White Light" pointing upward, under which a yellow layer labeled "Phosphors" converts the light from a magenta base labeled "Blue or UV LED."
- The middle section is labeled "Color-Mixed LED," displaying another upward-pointing arrow labeled "White Light." Below this, a block labeled "Color mixing optics" is overlaid on blue, green, and red squares labeled "Multi-colored LEDs."
- The third section named "Hybrid Method LED" also features an upward arrow indicating "White Light," above a similar "Color mixing optics" layer. Below it, alternating red and magenta squares are labeled "Colored and PC LEDs."
Beneath these diagrams, a gray panel holds descriptive text for each method:
- "PHOSPHOR-CONVERTED LED: Phosphors are used to convert blue or near-ultraviolet light from the LED into white light."
- "COLOR-MIXED LED: Mixing the proper amount of light from red, green, and blue LEDs yields white light."
- "HYBRID METHOD LED: A hybrid approach uses both phosphor-converted and discrete monochromatic LEDs."
These innovations have allowed these bulbs to be suitable for general lighting in residential applications. These bulbs last for 5-10 years depending on their usage. Now, you can find them in almost every store, and they look something like this.
