ABCs of LEDs: Lighting Metrics

Posted by kbanks & filed under LEDs, Lighting.

Have you ever been confused by some of the terminology surrounding LEDs – words like “efficacy” or “correlated color temperature?” If so, you’re not alone.

We recently attended an educational webinar, ABCs of LEDs, presented by Residential Lighting magazine. The course offered a wealth of information on LED lighting technology – including lighting metrics.

Here’s a quick overview of the key terms and what they mean:

  • Lumen – the most common measure of light output.


  • Watt - measure of electric power; the rate at which electric energy is transferred by an electric circuit.


  • Efficacy – the light output emitted by a light source, divided by the nominal light source wattage and expressed in lumens per watt (lm/W).


  • Correlated Color Temperature (CCT) – a measure of the color appearance of a white light source. CCT is measured on the Kelvin absolute temperature scale.


  • Color Rendering Index (CRI) – 0-100 scale used to compare the effect of a light source on the color appearance of its surroundings. A higher CRI means better color rendering, or less color shift. CRIs in the range of 75-100 are considered excellent.

Are there any other terms you have come across when considering LED lighting?

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