LED and Power: Quality Matters
October 18, 2012
LED replacement lamps look super-efficient on payback charts and utility bills, but they may be sucking more power than you realize.
GreenSpec and EBN have reviewed a number of LED replacement lamps over the years and have reported on improvements in efficacy (light output in lumens per watt of electricity consumption), color, and light quality; lower costs; and its increasing acceptance.
In the EBN article LEDs: The Future is Here, we explored briefly how LEDs interact with the power supply, but we were surprised when an email from Stefan Bernath, Alberta infrastructure energy coordinator, came in describing how LEDs were affecting his building’s power supply.
His email got me wondering if power quality and LEDs are going to be a bigger problem in the future.
Efficacy and power quality
Some 60-watt equivalent LED replacement lamps now have efficacies of over 90 lumens per watt (lpw) compared with only about 14 lpw for a standard 60-watt incandescent. When an incandescent bulb uses power from the utility, it may not be very efficacious, but its power factor (PF)—basically the amount of power coming from the utility used by the lamp—is 100% (1.0 on a scale of 0.0 to 1.0).
LED luminaires with separate drivers have power factors greater than 0.9, which is excellent, but an LED replacement lamp only can have a PF as low as 0.5 (Energy Star requires a PF of 0.7; those lamps are listed in GreenSpec).
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What is PF? Nancy Clanton, P.E., president of Clanton and Associates, used the following analogy: “If I pour beer into a glass and get some beer and a whole bunch of foam, the beer is the watts, which is usable power, but the foam is not usable.”
In other words, power factor represents the percentage of drinkable beer you have in your glass.
A customer using a 10-watt LED with a PF of 0.5 only pays for 10 watts, but the utility would have to generate twice that power in volt-amps to run that lamp; we end up thinking that we are saving more energy than we are—and the utility is paying for our foam.
Though the 20 volt-amps generated by the utility to run that LED is still much better than the 60 required to power the incandescent, as LED replacement lamps gain more market share, those 10 foam-like volt-amps are going to add up. If the true goal is to maximize the efficiency of utility power, use less fuel, and create fewer emissions, then the LED industry has some work to do.
Other LED inefficiencies
LEDs can have another effect on power in a building. “LEDs are diodes and are trying to take a sine wave and turn it into a DC signal,” said Clanton, “and whenever you do that, you get garbage and junk on the line.”
This garbage is known as total harmonic distortion (THD). THD could potentially shorten equipment lifespan, increase power losses on the transmission line, heat up transformers, and affect the performance of the LEDs and other electronics. THD was a problem for early fluorescent fixtures and computer “cube farms,” and Clanton is worried we are repeating history.
According to Bernath, his team replaced about 500 40-watt and some 100-watt incandescent lamps with 8- and 12-watt LED replacements, respectively, at the Alberta Legislature Building (partially due to high replacement costs for incandescents in the high-ceilinged rooms). When electricians went back and measured power consumption, the team was surprised.
Though the energy savings were big (he predicts a payback of 0.64 years), they discovered that the THD of the LED replacement lamps was over 66% for the most efficient lamp on the market. “It [THD] was a big concern because it increased the current on the neutral wire,” he said.
Bernath is not too concerned because LEDs make up such a small percentage of the building’s overall load, and the gauge of the neutral wire can handle it, but wonders what the impact will be on the transformers and other equipment.
The lamps used in the Alberta Legislature Building were A19-style LED replacement lamps, which are meant to replace standard screw-mount incandescent lamps, primarily in residential applications.
Gary Trott, vice president of product management at Cree said, “For our lamps, our spec is 20% THD with a power factor of 0.9.” This is a commercial standard, and makes Cree’s LED replacement lamps eligible for utility rebates. As usual, achieving this performance comes at a price.
“You can save a lot of money by having lower power quality,” said Trott. The drive to lower the price of LED replacement lamps and the lack of tough standards mean that fewer manufacturers are going to care about PF—and, especially, THD—which could have unforeseen consequences in terms of the nation’s power quality.
A standard on the horizon, finally
Trott is part of a group in California developing the California Quality Lamp Specification, which would improve on Energy Star standards by requiring a PF ≥ 0.9, along with a color rendering index (CRI) of 85. Though the standard does not address THD directly, Trott says that THD and PF are closely related, and as you improve the quality of the lamps to achieve a PF above 0.9, THD typically improves and becomes less of an issue.
When the California standard is developed and manufacturers can show that their lamps meet it, we’ll raise the bar for products listed in GreenSpec. In the meantime, I’m curious if any of you have had experience with LEDs and power quality. If so, we’d love to get your input.