Is there still a flicker problem?
Glare is still a highly discussed topic in the lighting industry. But have you heard anyone talking flicker lately? In the days of the T8 and T5 fluorescent tubes, minimizing flicker was high up on the agenda for all serious players. One might wonder if LED was the end of flicker? Actually, the problem can be worse than ever, says Hillevi. The flicker is still there, it just changed character.
”When the light flickers visibly it is called “flicker” but when it is not visible it is called temporal light modulation, you might see the light flickering during eye-saccades or if a flickering object is moving in the visual field. When you cannot detect it - it is commonly called non-visual flicker or subliminal flicker, but the correct terminology is temporal light modulation, and the effects of it such as light arrays is called temporal light artefacts.”
”The flicker from LEDs can have higher frequency and modulation, making it not visible. The old kind of fluorescent tubes had conventional ballasts that switched the light on 100 times per second (in Europe) resulting in a soft 100 Hz sinus curve with a modulation of about 50 percent. LED technology is digital, meaning you in the worst case can get a square waved curve of a 100 Hz that is either on or off. In many cases there is a fluorescent that causes a longer cool of period, giving a softer waved curve, even sometimes a sinus curve, with a lower modulation. Sometimes the dimmer function of the LED drivers consists of pulse width modulation, PWM, causing an extended “off-period” that leads to higher modulation. The higher the modulation, the easier it is for the eye to detect it within some ranges. Dimming with PWM causes more reaction from us humans. According to a study, LED-flicker at 1,900 herz can also result in an uncomfortable lighting phenomenon called phantom array where the eye perceives a light trail from the light source”, Hillevi explains.
No rocket science
Many LED light sources are great and the technology has great potential, she states.
The problem is that we usually do not have drivers that are good enough to produce a flicker free or a frequency free LED light. To be on the safe side, we would need drivers with a frequency of more than 3,000 Hz, preferably more than 20000 Hz. Today, many suppliers offer 300-400 Hz.”
People who have a high sensitivity to visual stimuli are, unsurprisingly, also more sensitive to flicker.
”In our CCF-studies (Critical Flicker Frequency) we found out that about 24 percent of the participants were sensitive to flicker from LED lighting. This group suffered both eye problems and headaches after being exposed for an hour”, says Hillevi.
”What mostly surprises me, is that this is by no means rocket science. The problem can easily be solved, but I think there’s a lack of knowledge within the industry. Innovation Skåne has developed a completely flicker-free driver, it has no frequency at all. The device is easy to manufacture and it could not be patented, it is practically an open source, you can just ask for the CAD file. The solution is right in front of your eyes!”
