Blog – Ask a LED Tech Articles

What do these terms mean? I’d like to better understand measuring of light output  As we watch the evolving technology of LED lighting we are beginning to hear terms that may not be familiar to us. AYou may have heard terms like lumens, lux, candlepower and footcandle. These are all various terms for measuring light output. The most important term for today’s lighting consumer to understand is lumens. Lumens or the shorter version of luminous flux, called Lux is the more common reference. You will see lumens used on the package of new LED bulbs and fixtures as a unit of measurement. It used to be that we could purchase an incandescent bulb and it would be labelled as “60 Watts” and we knew approximately how bright it was. Now that same bulb would still show the 60 Watts for its power use but it should also show that it would emit 850 to 880 lumens of light output. A comparable LED fixture or bulb will now state 800 or 850 lumens and also show that it is going to consume perhaps as little as 10 Watts of electrical energy. Footcandle is a term you might see occasionally. Footcandle is a unit of measure of the intensity of light falling on a surface equal to 1 lumen per square foot. It has been replaced by the International System by the candela (1 lumen per square meter). It is fair to approximate 10 lumens or lux per one footcandle. This term is widely used in film and photography. It is also important to lighting designers, particularly in cases where lighting is being planned in a commercial space where safety concerns and sufficient light in a workspace to perform tasks are critical design elements. Rarely, however, is the household consumer concerned with footcandle measurements. “Candlepower” is not very relevant to household lighting. It is still sometimes used to describe the luminous intensity of high powered flashlights and spotlights. Narrow-beamed lights of all sorts can have very high candlepower specifications because candlepower measures the intensity of the light falling on a target, rather than the total amount of light emitted. A given lamp will have a higher candlepower rating if its light is more tightly focused. To get back to what will serve you best, just remember lumens for now. To help you understand haw many lumens equate to which incandescent wattage equivalent here is the most popular equivalents. o 40 Watts = approximately 540 lumens o 60 Watts = approximately 850 Lumens o 75 Watts = approximately 1150 Lumens o 100 Watts = approximately 1600 Lumens o 150 Watts = approximately 2200 Lumens Don’t be surprised that as technology advances, our language will change as well and we might need some new terminology to describe it. The 60-watt incandescent bulb is quickly becoming a dinosaur and will no longer be a meaningful point of reference.

By: John Cody