5 minute read
More Than Light Meets the Eye (and the Brain)
By James R. Benya, PE, FIES, FIALD
Long before the phrase “human-centric lighting” was coined, there were concerns about possible health and well-being implications of electric lighting. For example, circadian effects were known and understood, although the actual biological mechanism was not discovered until the late 1990s. Among other negative qualities of electric lighting, flicker was well known to be a problem with certain human maladies like photosensitive epilepsy, where flashing lights, flickering fluorescent and neon lamps, fireworks or highly contrasting patterns could trigger a seizure.
The cause? In simple terms, AC power causes flicker. AC power creates 120 pulses per second of light in North America (100 in Europe and many other places) that are particularly noticeable when viewing a moving object.
All in all, flicker has truly been an on-again-off-again challenge(1), in more ways than the obvious. Throughout the history of anthropogenic (“man-made”) lighting, the common light sources have varied between flicker-free and really bad, annoying, make-you-dizzy flicker. Incandescent lighting is pretty good because, even when used on AC circuits or with dimming, the heat of the filament causes it to continue to glow even as the voltage changed from positive to zero to negative. This is called persistence. Persistence allowed the solid-state electronic dimmer invented by Joel Spira(2) to work on AC power with incandescent lamps without causing much flicker.
Meanwhile, fluorescent lighting became important in general lighting for economic reasons. But the original fluorescent lamps emitted 120-hertz flicker which was noticeable and often irritating, if not the cause of nausea or worse. Two-lamp magnetic ballasts solved the problem by making the pulses peak at separate times to almost totally negate the flicker. Then, in the 1980s, high frequency electronic ballasts (including dimming ballasts) operating at 50 kHz or more eliminated flicker from our fluorescent lighting vocabulary. For a period of 30-35 years, the electronic ballast solved the flicker problem for fluorescent lamps, and flicker problems sort of vanished.
Then along came LEDs. LED lighting promised to give us a whole new way to light with lower first costs, less energy use and tremendous flexibility. The light emitting diode is, after all, a diode which is a basic electronic component. Hook it up to a battery or DC power supply, and an LED produces more light per watt of electricity than any other light source that could be used in an inexpensive luminaire, lamp or even a toy. The light it emits is smooth and flicker free as well as energy efficient.
But we don’t use DC power to light buildings. Edison lost to Westinghouse(3) because AC power has the ability to change voltage using transformers. So today, every LED luminaire or LED replacement lamp has a driver that rectifies AC to DC(4). And here comes the problem. In North American it is called “pulsing DC” at 120 hertz that causes LEDs to emit pulsing light, which is flicker, with all of its issues including being a visual distraction and affecting persons who are sensitive to it.
It’s possible to smooth out the pulses using capacitors, but capacitors are big, expensive and sensitive to heat. They are used in encased LED drivers where there is room but seldom in inexpensive and/or compact drivers. And generally not in linear LED lighting.
In my own home, we love LED linear cove lighting and undercabinet lighting, and we endure flicker because we want to be able to dim it. A long string of LEDs, such as for cove lighting, can’t employ high frequency DC because of significant losses along the string. These losses are the result of distributed inductance and capacitance in the string itself, and to make matters worse, the string becomes a radio transmitter that can cause radio frequency interference. And in our case, we operate the lights at full most of the time, rarely dimming and suffering flicker when we do. And tolerating when we really want to dim.
That said, I chose to write about this because I am aware of significant potential health and wellness issues resulting from flicker. Possible issues related to flicker include headaches, migraines, epileptic seizures, autistic repetitive behaviors, eye strain and fatigue, stroboscopic effects that make moving machinery appear to be standing still, and reduced visual task performance(5).
These issues stem from the hard-to-fix challenges of dimming LEDs. The scientists at the US Department of Energy (DOE) identified flicker as a problem associated with LEDs that could limit their acceptance and success. Pacific Northwest National Laboratories (PNNL) began research into flicker, also called temporal light modulation (TLM), in earnest. For starters. I recommend you download and watch Flicker Basics, a web page that offers Naomi Miller’s brief video(6) of the same name. As she states, “ LED lighting is wonderful in all ways except that, to vary it, we have to dim it. We need to stop and resolve the flicker problems, and it may take new technology.”
(1) Electrical engineering joke; a pun
(2) Founder of Lutron and whose invention of the electronic sold-state dimmer is exhibited at the Smithsonian National Museum of American History.
(3) The War of the Currents
(4) Drivers rectify AC to DC, and depending on the type of driver, quality, cost and physical space, they can smooth out rectified DC and eliminate flicker.
(5) US Department of Energy, “Flicker Basics” by Naomi Miller
(6) For this and related work, founded on her prior career as a scientist and as an accomplished lighting designer, Naomi received the 2024 IES Medal, the Society’s highest honor. The IES Medal is awarded to individuals who have made significant technical achievements that advance the profession, art, or knowledge of illuminating engineering. This award highlights the importance and impact of her work on the future of lighting.
