"Higher Efficacy Makes A Better Product"
Imagine you’re washing your car and you’re using an adjustable spray nozzle. If you set the nozzle to the widest setting, water is going to go everywhere, much of it into the air and – uselessly – not even hitting your car. To remedy that, you adjust the nozzle so that the hose’s stream is more focused – and now all of the water is hitting your car.
When translated to lighting terms, the “efficacy” of the hose is how much total water is leaving the tip, i.e., how much total light is emitted from an instrument. The “efficacy” of the hose goes down when you tighten the nozzle, but the impact of your hose has gone up dramatically. And I don’t know about you, but I’d rather have a more impactful hose, or lighting system, than something that just sprays out a lot of waste.
DON’T BE FOOLED
Efficacy is one of the most misunderstood and overrated methods of comparing lighting systems. The efficacy of a lighting system is a measure of its total light output; regardless of whether that light makes it to the desired target. A more meaningful measurement is foot-candles – a measure of the amount of usable, targeted light that will travel from the instrument to your desired location.
Unfortunately, many products are ranked by efficacy and not by the foot-candles actually delivered. When utility companies base rebates upon efficacy or especially when end-users use efficacy to compare products, such as those on the DesignLights Consortium Qualified Products List, higher quality products that distribute light effectively and uniformly appear less capable than inferior products.
HOW TO JUDGE
Overall, there are many metrics that are significantly more important, such as thermal management, delivered light quality, and the quality of the electronic componentry. Products should be evaluated for the quality of light they deliver relative to the application. Efficacy, in its traditional form, should not be on the list.