LED Efficiency – How It Works, Why Most Specs Lie, And What To Look For August 16, 2017 – Posted in: Lighting Information
In the lighting market these days, there is too much confusion about how LED efficiency works, what all the stats mean and if those stats match up to real life scenarios. In this article I’ll go over the stats to look for, common misleading marketing practices and how to determine the best efficiency per dollar. First we’ll start with the power source and work our way through to where the light falls.
LED Driver Efficiency
LED ballasts or drivers have a big effect on the actual efficiency of the fixtures you install, especially the power factor. Pay attention to the model and power factor when purchasing commercial fixtures, since a low PF cost you a lot of money over time. The most simple explanation of power factor we found was from a reddit thread on /r/ELI5 :
Alice buys stuff from Amazon and they ship it to her and she likes it and keeps it. Everyone is happy! Alice has a power factor of 1.0.
Bob buys stuff from Amazon and they ship it to him but he doesn’t like half of it and returns it. Amazon likes that they’re selling stuff to Bob, but they’re kinda annoyed that they have to deal with all the shipping costs associated with the stuff that he returns. Bob has a power factor of 0.5.
If a device has a power factor of less than 1.0, it means that it is not actually consuming all the electrical power that is sent to it down the wire — some of that power is reflected back into the grid. Utilities don’t like it too much.
For commercial lighting, try to stick with PF above .95 so the efficiency loss is only 5% . Very few LED drivers can go above PF .95 .
LED Chip Efficiency
When LED chips are tested, many people don’t realize the testing takes about 20 milliseconds and the efficiency testing takes place in the bare chip in optimal lab testing environments. They get sorted by bare efficiency and quality before labeled with their model numbers (similar to how computer processors might sell the same chip with better silicon inside). Bare LED diode testing gives them the best possible “stats” or specs on their chips which in turn gets used in marketing materials. Many manufacturers will use bare LED chip efficiency on their final product marketing, which is basically “stat padding”. The true efficiency can be as much as 25-40% off.
Color temperature in LED chips determines their efficiency. If you look at our high bay lighting chips that we use in our product (Philips Luxeon Lumileds 3030 2D), you’ll see the difference in efficiency based on the color temperature you use. This is why most commercial lighting is 4000-6500K , otherwise you’re just throwing away money. For maximum efficiency you sacrifice CRI as well.
|TYPICAL LUMINOUS FLUX (LM)||TYPICAL LUMINOUS EFFICACY (LM/W)||PART NUMBER|
Diffusers, Dust & Dirt
No matter how you look at it, diffusers lower the efficiency of your fixture. Even the clearest lenses will have some effect on the light output. On top of that, the sides sides of the fixture can also trap light inside which lowers the total output.
Unless your installing lights that are going into an intel computer chip facility, your lights are bound to get dust and other particles on them throughout the years. This will in turn lower the light output to the ground floor. IP65 lights ensure dust doesn’t get inside, but the lens can still get dirty over time. Is it worth it for you to clean the dust off each light? Of course not, but it is something to think about.
Overall, you usually don’t need to buy “extra” lumens to compensate for this, since almost many companies in the market is going off the LED chip lumens (unless you have the photometric testing data). Just make sure to consider these factors and keep an eye on the right specs when purchasing lighting.