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LED guide: LED terms and definitions you need to know  

LED guide: LED terms and definitions you need to know  


This term is used differently in the lighting world than in the regular consumer world, where lamps are devices that sit on your end table and have one or two bulbs in them. The correct lighting terminology for the fluorescent tube is a fluorescent lamp, which fits into a fixture (or sometimes luminaire). Lamps are always replaceable light sources units, separate from the fixture.


A light-emitting diode (LED) is a semiconductor junction: Two dissimilar compounds that don’t do a particularly good job of conducting electricity – until you apply a forward voltage, Vf,across the junction,  at which point current flows just fine. In an LED, in addition to current flowing across that junction, the junction also emits photons, or light. LEDs emit light in only one wavelength, or color.  The most common colors of LEDs are red, yellow, green, and blue.

White light is the presence of all wavelengths, so making a white LED is more complex. The most common and inexpensive way is to take a blue LED and cover it with a phosphor. When the blue light strikes the phosphor some of the light passes through as blue, and some excites the phosphor which then emits its own light — mostly yellow, but some red in there two. The combination of the three colors of light is a white light.

The components we usually think of as LEDs, such as the low-power indicator LED or the mid- or high-power LEDs used in bulbs and luminaires, are packaged LEDs; The bare LED itself, before it’s packaged, is called a chip.

Vf is typically 2-3V. A big advantage of packaged LEDs is that all the LED chips are connected together internally to the package in a string so that their Vf add up to a much higher voltage: An LED package with 10 LED chips inside, all with a Vf of 2.25V, will have a Vf for the LED package of 22.5V. And 22.5V is much easier for a LED bulb designer to work with than 2.25V.

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