BENYA’S ART & SCIENCE
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 challenge1, 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 Spira2 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 Westinghouse3 because AC power has the ability to change voltage using transformers. So today, every LED luminaire or LED
“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.” — Naomi Miller 16
designing lighting