Decoding the Lumen
A new term for most LED light bulb shoppers is the lumen. Just what is it? What does it tell me about the lighting I’m buying? How can I compare lumens to watts? These are a few of the questions we’ll discuss.
Lumens are the International unit of luminous flux, a measurement of the power of light visible to the human eye which also takes into account the eye’s ability to perceive light at different wavelengths. The technical definition gets pretty confusing to the non-geeks with terms like steradians and solid angles, but in layman’s terms the lumen can be thought of as the quantity of light being output from a given light source, such as an LED bulb.
Upcoming regulations stipulate that all light packaging will be required to list light output in lumens, and this change will simplify the comparison of different lighting technologies easier for the consumer. No longer will one have to wonder how an 8 watt LED bulb compares to a 14 watt compact fluorescent or a 40 watt incandescent, as knowing the lumen output will level the playing field. For instance, a brand new 60 watt incandescent bulb typically outputs 800 lumens of light and a 75 watt incandescent bulb generates about 1,100 lumens of light. The correlation with incandescent bulbs being that the higher the wattage the greater the light output. All this changes when considering an LED bulb as the new 60 watt incandescent replacements output 800 lumens while drawing only 12 watts of power. The take away from this example being that lumens don’t truly compare to watts as one is a true measurement of visible light output and the other is a measure of the power required to light the lamp.
Knowing both the lumens and watts for lighting products is a great thing as it allows us to understand something about the light’s efficiency. For instance, the efficacy of the standard 60 watt incandescent is approximately 13 lumens/watt (800/60) while the LED replacement bulb is approximately 67 lumens/watt (800/12). This equates to the LED bulb being 80% more efficient than the incandescent bulb it replaces. That is a huge improvement. For most LED lighting products the minimum efficacy to earn the ENERGY STAR® qualification is 50 lumens/watt.
Although there are other considerations to take into account when buying lighting products, having a basic knowledge of what the lumen is and how it helps us to understand light output and efficiency will simplify the process of buying light bulbs in the future.