Flickering and Other LED Anomalies

Feb. 8, 2016

Have you encountered these odd LED behaviors?

I have done informal tests of more than 100 LED products from a variety of credible manufacturers to see how different systems perform. In my experience, most LEDs work great. However, I have seen some anomalies that I will share with you so you don’t pull your hair out when unexpected LED weirdness occurs.

Impacts from Dimming and Inconsistent Voltage

Many of you already know that certain LEDs do not perform well with certain types of dimmers. LEDs can flicker intermittently or prematurely burn out. For a simple wall switch, it's good to have a dimmer that has multiple adjustment possibilities, such as variable light output as well as variable "kickstart." Although I have seen good performance with these, some LED brands will occasionally flicker even with a good “LED compatible dimmer.” I hope that in the future LED and dimmer manufacturers will list compatible brands/models on their packaging.

Power quality and consistent voltage is another prerequisite for good LED performance. If your electrical system’s voltage is occasionally strained by a relatively large load (motor, refrigerator, laser printer, etc.) and the voltage drops, you can witness a half-second blink from the LEDs. This makes sense because the LEDs do not have a transformer (like fluorescent systems do) that absorbs voltage spikes like a car’s shock absorbers dampen bumps for a smooth ride. Incandescent lamps also blink if the voltage drops; however, because incandescent lamps “glow,” the blinking isn't as noticeable.  

Another anomaly I had heard about – but didn’t initially believe – is that a single compact fluorescent lamp (CFL) can influence LEDs on a different circuit in the same building. I actually witnessed this anomaly and saw my LED lights flickering until I unscrewed the one CFL in the building, and the LEDs stopped flickering. I cannot explain this phenomenon other than that the CFL must have been generating some harmonics that traveled back to the breaker box and influenced the other circuits. For curiosity’s sake, I ran tests on the LEDs and CFLs and found lower harmonic distortion in the LEDs than in the CFLs. 

I Become an Investigator in My Own Facility

I witnessed most of the previously mentioned anomalies when my wife and I bought a two-story building and renovated the first floor (about 4,000 square feet) for her new medical clinic. We decided to use recessed can fixtures with screw-in LEDs, and we picked a major brand for these LEDs. I chose screw-in LEDs because I figured that as LEDs continue to improve over time, we could upgrade the lamps easily in the future.

As we prepared for the grand opening, we noticed that the LEDs were flickering about 10 times per hour. It was noticeable – as was my wife’s frustration with me, her landlord and “energy expert.” For my own survival, I changed the LEDs to a different brand, installed different dimmers and made several other modifications to correct the problem. No improvement. I even tried putting battery backups/capacitors/surge suppressors on all of our printers so that the voltage drop caused by them would be minimized. Despite all my modifications downstream from the breaker box, the problem did not improve.  

One day, I looked outside the building and noticed that my 2nd floor tenant's HVAC condenser was cycling on and off about every six minutes or so and that this behavior correlated precisely with the LED flickering inside our clinic. The electricity serving both floors comes from a shared bus bar outside the building, so I thought that I had identified the problem. I checked the inrush (start-up) amp draw from the 2nd floor condenser – but it was normal.

I asked the utility to test the supply line’s voltage coming from the utility pole. A lineman took measurements and assured me that the voltage was fine and consistent, yet at the same time, the 2nd floor condenser was cycling and I could see the lights inside the building flicker. I was frustrated.

Luckily I noticed that the lineman’s measurement instrument used a five-second average that could not detect a voltage drop lasting only one-tenth to one-half second. I explained that it was similar to saying that because the temperature is 72 degrees outside today, it's going to be 72 degrees all the time for the next five days. The lineman didn't agree, and the flickering continued. The pressure from the wife increased.   

Finally, we got the utility's engineers involved. They quickly determined that just prior to the renovation, they had moved our building's pole-mounted transformer about 300 feet down the road, too far away to maintain voltage. Once the transformers were relocated next to our building, our supply voltage became more consistent and almost all of our LED flickering went away. However, even today if I put a certain brand of CFL into a socket in our building, I see the other LEDs flicker, apparently from the harmonics! So I have had to coach employees to buy LEDs only and never install a CFL.

The Importance of Testing Before Buying

Whatever you do with your LEDs, make sure you test several samples in your own building/circuits before you buy thousands more. You want to make sure the system works without flicker or other problems. The anomalies mentioned in this article are rare, but at least you’ll know you’re not crazy if you experience them.

I would love to hear your stories about weird lighting problems. Please email me at [email protected].


Eric A. Woodroof, Ph.D., is the Chairman of the Board for the Certified Carbon Reduction Manager (CRM) program and he has been a board member of the Certified Energy Manager (CEM) Program since 1999. His clients include government agencies, airports, utilities, cities, universities and foreign governments. Private clients include IBM, Pepsi, GM, Verizon, Hertz, Visteon, JP Morgan-Chase, and Lockheed Martin. In August 2014, he was named to the Association of Energy Engineers (AEE) Energy Managers Hall of Fame.

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