The EU recently corrected a minor deficiency in the rating system they use for lighting on the European continent by introducing “useful lumens.” The United States and previously Europe evaluate lighting solely in terms of lumens (vice useful lumens). As you might imagine from the new terminology, there is in fact, such a thing as a useless lumen. Does that mean that ratings speaking solely in terms of lumens are potentially suspect? Somewhat yes and somewhat no. We’ll explain.
Image From Breitbart.com
First, why the change? And is it a good thing? Yes, the change is positive in terms of overall objectivity regarding light output. The major deficiency in reporting solely lumens is that total lumen output is calculated in all directions. Most bulbs, in fact, radiate in all directions. Think of your standard incandescent bulb, or a fluorescent light, or any type of gas-discharge bulb – they all radiate light for 360 degrees. This might not seem like a big deal but it’s actually a huge limitation inherent to these older technologies. Consider a fluorescent bulb in a ceiling fixture. The only relevant area in the room where lighting is desired is down. Nobody benefits from light focuses at the ceiling. As a consequence approximately half of the fluorescent lighting in a room requires light reflectors and redirectors to point it at the target area. Of course there are inefficiencies in this type of system because much of the redirected light is lost (called “waste light”). Waste light is somewhat eliminated with technologies that produce naturally directional light. For example, LED technology naturally emits light for 180 degrees. So an LED in the same situation as the aforementioned fluorescent bulb will not require any redirection or reflection – meaning it will not have the associated “waste light.” For this reason, the new rating of “useful lumens” is particularly relevant to LED technology. LED technology is unfairly compared to legacy lighting technology when comparing lumens. A lumens rating for the fluorescent bulb we previously discussed would give credit for 100% of the output. It should really be penalized in its rating based on all of the waste light it produces that is never actually seen by the end-user. Useful lumens takes this into account.
Another way to think of the rating change is “source” versus “system” efficiency. Source efficiency is a rating very much parallel to total lumen output. This rating, however, is also misleading because there isn’t a single bulb in existence whose system efficiency (its efficiency in an actual, real-world application) is the same as the source efficiency (its efficiency in a lab where omnidirectional light emissions are counted equal to directional light emissions). Since we care about system efficiency – how much light we get on the target area per unit of energy consumed to produce it, system efficiency is the relevant metric for comparative analysis.