LED Vocabulary Quiz

a guest post by Lisa J. Reed, Lighting Designer

LED Vocabulary Quiz

Just when you figured out what CFL, color temperature and CRI meant, LED came along and changed the entire vocabulary. Here are a few words, phrases and acronyms you will want to know when discussing LEDs.

LED fixture systems use semiconductor technology instead of filaments or arc tubes. SSL is the abbreviation for Solid State Lighting and refers to any type of lighting that uses diodes for illumination.

All LED fixtures include an LED driver or power supply. Just to make it confusing, though, this driver can be integral to the fixture, separate from the fixture or remotely located. I have even heard rumors of a driverless LED, but that’s kind of like the driverless car for now. Typically, the driver is an important part of every LED system, and you should remember it is a factor when using LED fixtures.

LED manufacturers sort their products into bins based on lumen output and color. Fixture manufacturers specify a range of bins from which they will accept LEDs. If they only accept fixtures from bins that are very close together, the diodes are more expensive, but result in a higher quality fixture. If fixtures are built with LEDs from a wider range of bins, cost and lead-time are reduced. Manufacturers may refer to their “tightly binned” products when they want to convey that theirs is a good quality product.

RGB stands for Red, Green and Blue. An RGB LED fixture has all three colors of LEDs, which when blended can create almost any color, including white. This is the technology used in most of today’s fabulous color-changing light fixtures. Sometimes manufacturers use four different LED colors in their fixtures – RGBW. RGBW fixtures include a separate high quality white LED. A special controller is required to change the color of the fixture in an RGB or RGBW product.

Dynamic White
Some white LED fixtures can offer a range of white color temperatures, from a warm 2700K to a cool 6000K. There are different names for this technology, including variable white, adjustable white, tunable white and dynamic white. Again, a controller is required to adjust the light from a warm white hue to a cool white hue.

Warm Dim
Slightly different from tunable white, warm dimming technology is coming into vogue today. With an incandescent lamp, the more you dim it, the warmer in color it becomes. When you dim it all the way down it becomes just a glowing orange filament. However, when an LED is dimmed, the color temperature does not change. Some people prefer this warm color temperature at low light levels, or just want their LED fixtures to better mimic incandescent. Warm dim technology is achieved by incorporating red and/or amber LED diodes into a white LED light fixture. Control technology is used to illuminate the warm sources as the fixture is dimmed to low levels.

L70 describes the brightness of an LED after a number of hours – often 50,000. If a product claims L70 after 50,000 hours, it means that after 50,000 hours of burning (nearly six years if the lights are on 24/7) the lights are now 70% as bright as they were when they were first installed. L70 doesn’t mean anything without the corresponding number of hours. You may also see terms such as L70 at 6,000 hours. Sometimes manufacturers will list L80 (or even L90) at 50,000 hours. This simply means that after 50,000 hours, the LEDs will be 80% (or 90%) as bright as they were initially. Be careful not to confuse L70 with LM79 or LM80...

This IES document applies to LED fixtures (but not to components.) It prescribes the approved method for “Electrical and Photometric Measurements of Solid-State Lighting Products.” In the beginning, LED products were the wild, wild west. Manufacturers claimed just about anything based on their own personal “test procedures.” LM79 gave structure to the chaos and today LM79 compliance can help ensure that you are comparing apples to apples when you read LED product literature.

This IES document describes the approved method for “Measuring Lumen Maintenance of LED Light Sources.” It applies to bare LED light sources and does not cover complete luminaires (fixtures.) The main story here is usable life. LED sources, like the old metal halide lamps, tend to fade over life instead of “burning out.” Again, when manufacturers are using the same test methodology, you can be comfortable when comparing products.

That’s a lot to digest. Make sure you’re ready for the vocabulary quiz...

Hurry and learn these LED words before an entirely new technology like FIPEL hits the market with its own glossary of terminology!


Lisa J Reed photo - Lighting Blog

Lisa J. Reed has been attracted to lighting (like a moth to a flame) for 20+ years. She is the Founding Principal at Envision Lighting Design, LLC in St. Louis, where she designs, teaches, and writes about architectural lighting.


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