LED Lighting Types

RGB---Red, Green, and Blue Together

• There are two basic approaches to producing LED lights. The first is to assemble several different color LEDs together, mixing their outputs to create white light. Most often, red, green and blue LEDs are combined in a single assembly, but other color combinations can also create white light. This approach allows the output color to be changed simply by changing the relative amount of current sent through the individual diodes.

Phosphor

• The second basic approach to building an LED for white lighting is to couple a blue LED with a phosphor. A phosphor is a material that absorbs light of one color and emits light of another color. Some of the short-wavelength blue light gets absorbed by the phosphor, which emits yellow light. The yellow combines with the portion of the blue light that isn't absorbed, mixing to make white light. The relative simplicity of this approach makes phosphor-based LEDs the predominant choice for applications that don't require color changing.

Replacement Bulbs

• Whichever light generation mechanism is chosen, one application of LEDs is in replacement bulbs. These are bulbs that are intended to fit in the same sockets and volume as the "A" bulbs, such as standard 60- or 100-watt incandescent bulbs. Either RGB or phosphor LEDs can be used for these bulbs. Check the Department of Energy's (DOE's) Lighting Facts website, or the lighting facts label on the package, to verify the output characteristics of the replacement bulb. If it doesn't have a lighting facts label or an Energy Star rating, it's probably of suspect quality.

Purpose-Built Luminaires

• "Luminaire" is lighting industry speak for "light fixture." With incandescent and fluorescent bulbs, the same bulb can be put in a variety of luminaires. With LEDs, the distinction between bulb and luminaire is not clear. Purpose-built luminaires have LED chips laid out specifically to match the physical layout of the fixture, rather than LED bulbs inserted into a standard socket. Luminaires can, and often do, contain a combination of RGB, phosphor and even single-color LEDs.

Luminaire Categories

• The DOE recognizes installation-ready LED luminaires in their annual "Next Generation Luminaire" program. The DOE recognizes more than 15 categories of luminaire, such as "Surface Mounted General Illumination," "Recessed Accent Lighting" and "Portable Desk Task Lighting." In addition, there are unique specialty luminaires that don't fit any of the existing categories. Examples, and a complete list of categories, can be found at the Next Generation Luminaire website.