Which do I use to specify LED lighting, lumens or watts? To answer this question, let’s review their simple definitions
A watt is the amount of power needed to transfer one joule of energy per one second.
A lumen is the scientific unit of luminous flux. Luminous flux measures the amount of visible light emitted during 1 second in all directions. The human eye perceives this as the “brightness” of a light. The more lumens the brighter the light.
Based on these definitions, lumens would seem to be the logical choice, but that wouldn’t tell the whole story. Historically when they were fewer choices, lights were generally specified in watts. For a given power level (w), a light produced a given amount of lumens (lm) and traditionally watts were the accepted measure of brightness.
However, with the emergence of new lighting technologies like Halogens, CFLs and most notably LED Lighting, the relationship of lumens to watts began to vary greatly. The new lighting landscape could no longer be specified by watts alone without also considering the lumen output.
So to answer our question, lumens and watts are both equally important and should be specified together as lumens per watt (lm/w). Watts are the power that drives the light to produce lumens. The more lumens produced per watt (lm/w), the brighter the light will be for the same power consumed.
This relationship is known as luminous efficacy, or the efficiency of a light. Today’s energy protocols require that lumens per watt (lm/w) be specified to easily identify the most efficient lighting. LED lighting produces the most lumens/watt by far, making it the most efficient, cost effective and environmentally sound choice in lighting.
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