The Invisible Threat of Light Flicker

Everyone has seen the flickering light movie cliche; A good cop/bad cop interrogation scene with a poorly lit room or a horror movie with the audible flicker and buzz in a haunted basement.  Whether it’s a movie cliche or in real life, there’s a reason why movies use flickering light as a tool to create tension and to make the audience uncomfortable.

The real-life effects of light flicker can range from annoyance, distraction and discomfort, to headaches and even seizures.  Visible flicker has long been considered a problem but was previously tackled back in the 90s by using high-frequency electronic ballasts with fluorescent lamps.  Further improvements to lighting technology, like the introduction of LEDs, has helped reduce visible flicker but problems still remain as not all lighting schemes are created equal.

LED solid-state lighting (SSL) is much more efficient than previous fluorescent and incandescent lamps, so it has easily become the universal replacement as the world becomes more energy efficient.  However, the industry has not done enough to address the causes of flickering LEDs that lead to health issues.

The distressing element of LED flicker is that it is often invisible to the human eye and viewers may not be consciously aware it is taking place.  This can cause serious health problems to those with photosensitive epilepsy or those prone to migraines.  It can also be problematic for businesses as it can cause employees to feel distracted, uncomfortable, unmotivated and cause eye-strain.

So how does this happen?  Let’s get into the science behind flicker:

  • Stroboscopic effect (flicker) is present in nearly all sources of artificial light
  • It is caused by the fluctuation of light output as the diodes within the light switch on and off at extremely high speeds
  • The rate of the switching is measured in Hertz (Hz); the number of cycles per second
  • The varying health effects are varied by the frequency at which it occurs
  • From ~3-70Hz there is the risk of flicker causing epileptic seizures
  • Flicker can cause discomfort, headaches, vision problems, etc. up to 165Hz
  • Some can perceive flicker up to 200Hz
  • Every electrical network on earth is 50Hz or 60Hz frequencies

However, why are we seeing these fluctuations as LEDs are supposed to be solid-state and run with constant current?  The discrepancy occurs since most buildings are powering their lighting with alternating current (AC) instead of direct current (DC) as intended.  Flicker and brightness issues are created in phase with the cycle of AC at the 50Hz or 60Hz. This frequency can cause plenty of flicker while dimming LEDs since anything below 200Hz can be visible.  A driver can be installed to fix this issue but they also create ripples in the voltage at the tune of 120Hz.

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