When we evaluate a luminaire’s quality, the criteria of flicker and the stroboscopic effect play an important role. They can seriously impair people’s well-being at work and, in the worst case, cause grave dangers.
How does flicker arise?
All mains-powered light sources pulsate since the polarity changes many times a second with AC supply. The light source insists directly on this current weakness. We indicate the intensity or number of polarity changes (most recent fluctuations) in the unit “Hertz” (Hz). The typical household alternating voltage of 230 volts (EU) has 50 Hz or 60 Hz.
Fig. 1: Sinus curve (time t = 1s) of a normal household AC voltage
There are 50 or 60 voltage pulses per second and thus 100 or 120 zero crossings. Two for every complete voltage wave (sine wave). With every zero crossings, the light source’s polarity changes are not supplied with power for a short moment. The result is a flicker.
Fig. 2: Example flicker
In general, this is particularly problematic with conventional light sources such as fluorescent tubes and halogen lamps. This flickering of the light source is often difficult to see with the naked eye. See more clearly when holding out a cell phone camera.
We, humans, perceive this flicker as being uncomfortable. Health problems such as headaches, difficulty concentrating or malaise can occur. Stroboscopic effects are also a common hazard associated with flickering light.
A stroboscopic effect is a movement illusion. It consists of moving objects resting or appearing in a different state than their actual state when illuminated by periodically changing light.
As a result, the user can be brought into dangerous situations by stroboscopic effects in that the perception of rotating instruments is changed. We can reduce the risk of accident at work by using a flicker-free and adapted light source.
Fig. 3: High risk of stroboscopic effects when working with rotating tools, e.g. in workshops
How can we avoid these effects?
A common opinion is that LEDs are a solution for entirely flicker-free lighting. In contrast to conventional light sources, we operate them with a constant current – the polarity of LEDs does not change. The LED ballast ensures that the alternating sinusoidal curve flows on the direct current side and that additional smoothing capacitors flatten the characteristic curve shape. The assumption that LEDs can offer a solution for flicker-free light without stroboscopic effects is correct. However, you should note that we cannot operate LEDs with perfect DC – the light can flicker. The reason for this is usually the poor quality of the LED ballast or the dimming method. Accordingly, flicker and strobe effects also play a role with LEDs, but from a different perspective than conventional light sources.
You can find more about flicker and the stroboscopic effect with LEDs in the article “flicker and stroboscopic effects with LEDs.”