Domestic and international lights utilize some form of alternating current as an electricity delivery mechanism. A light that flickers is observed to change its lighting intensity as the voltage through the lighting fixture alternates or when power line voltages fluctuate. Alternating current operates on cycles of 50 to 60 hertz, which means that electrical power through a light fixture turns on and off 100 to 120 times every second. Human sight perceives flicker at lower frequencies (generally in the 10 to 25 hertz range) and flicker has generally not been a problem with incandescent lights that operate on higher frequency power grids.
Solid State Lighting Drivers
Solid State Luminaires (SSL’s) that produce light with LED technology are more likely to cause flicker sensations when their LED drivers are not engineered properly. LED drivers are the embedded power sources in SSL’s that convert alternating current into the low-voltage direct current required to power the LED. LED drivers typically operate at constant voltages between 2 and 24 volts, or constant current of between 350 mAmps and 1 Amp. LED drivers enable dimming, color changing, or sequencing of luminaires. Most current-generation LED drivers are also compatible with low-voltage control devices that further expand the capabilities and versatility of LED lighting systems.
Early generation SSL’s used commercially available LED drivers that did not properly match the LED luminaires. Those commercial drivers generated an AC ripple current which pulsed through the LED’s at frequencies that were low enough to be observable as flicker. Certain types of power modulation techniques that were used to dim LED’s also resulted in light flicker. Engineers and lighting designers quickly identified these problems and responded with custom LED drivers that were more compatible with dimmers and control circuits that had been designed for SSL’s.
Solving the Flicker Problem
Much of the recent research on flicker reduction has focused on fully electronic drivers that utilize pulse width modulation technology to eliminate underlying ripple effects. Electronic digital drivers eliminate flicker by increasing power frequencies into the hundreds or thousands of hertz, at which levels a human eye is unable to sense any flicker. Pulse width modulation allows LED’s to be fully dimmed from 100% illumination down to 0% with no color shift or loss of LED performance.
Lighting designers and architects who specify LED lighting systems for buildings can address any question of flicker by including proper specifications for LED drivers that match the chosen SSL’s. Outdoor LED lighting applications in which luminaires will be exposed to temperature extremes will call for different driver specifications than indoor applications that put less environmental stress on a system. Designers who have any questions about LED driver specifications should consult with engineers and technicians who can evaluate the likely system stresses and recommend the proper driver for that environment.
Significant amounts of research time and energy are currently being devoted toward increasing the lighting industry’s knowledge of flicker, including whether flicker can cause any adverse health effects. There is no conclusive evidence of health problems when individuals have been exposed to high-frequency (i.e. unnoticeable) light flicker over shorter periods of time. The current research is examining the longer-term effects of that exposure.