The stroboscopic effect is usually taken to mean the visible flickering (flicker) of light; however, this is incorrect. Flicker consists of the frequency and modulation. Flicker can lead to annoyance, fatigue, headaches and difficulty concentrating. It is caused by too low a frequency and/or modulation of light. At a frequency of 50Hz, the light goes on and off every 0.02 seconds. The frequency at 50Hz is visible to many people and hereby causes the previously mentioned inconveniences. This flicker is also perceptible to animals and is also disturbing. In addition to the base frequency, frequency modulation is also an important aspect that determines the level of flicker. Modulation refers to the intensity of each wave. A Flicker meter is used to measure frequency and modulation. Through the Flicker Index, the cycles are displayed graphically and the degree of disruptive flicker is illustrated.
On the IES website, this image is shown to graphically represent the creation of the Flicker index.
The cycles are analyzed by modulation and frequency.
Where previously incandescent and halogen spotlights and other heat emitters were the dominant light sources, now LED is. A heat radiator depends on a thermal process. This process creates emitted radiation that becomes visible to the human eye under certain conditions. It is a relatively slow process in which the stroboscopic effect occurs less. Since the electrical grid in the Netherlands operates at 50Hz, and this frequency was transferred 1 to 1 to the radiant heater. LEDs are not heat emitters, which means there is no slow thermal effect where the frequency amplitude is somewhat smoothed. The on/off switching at every 0.02 seconds is therefore visible and disruptive. A well-developed LED Driver overcomes this problem.
Want to know more about LED Drivers?
Flicker does not affect everyone the same way. However, for everyone, “tying” images together will be similar. When focusing, the eyes and brain are extra challenged to make it a fluid image. This concentration takes energy and creates extra effort. Both from visible (on/off) and invisible flicker (modulation) can cause health problems. These complaints are characterized as: incorrect work posture, eyestrain, irritation, decreased concentration, reduced vision, headaches and in some cases much more serious complaints. Even if a person is not experiencing conscious symptoms from the stroboscopic effect now. It does not mean that the symptoms are not there, or that they are not going to arise. Established long-term health complaints include chronic fatigue, chronic migraines, light sensitivity, anxiety, depression and irritability. Basically, then, there is no valid reason to say that a disruptive level of flicker is acceptable.
The cooperation between our eyes and brain makes flicker less visible. Or sometimes not visible at all, that does not mean it is not there. Even non-visible flicker can have adverse effects. With a phone camera, it is easy to determine if the frequency is out of sound range (<90Hz). If black stripes are observable, it means the modulation should be extremely low in order not to risk adverse health effects. It is best to use professional equipment to measure the flicker. Clearlight includes Flicker value in its lighting audit by default.
Sources consulted:
https://www.ies.org/definitions/flicker-index/#:~:text=5B5%5B5.9.,curve%%20a%
https://www.alexfergus.com/blog/light-flicker-health
http://www.bio-licht.org/02_resources/info_ieee_2015_standards-1789.pdf
http://bio-licht.org/02_resources/info_ieee-pem_2014-09_led-flickering.pdf
Clearlight uses portable devices for its Flicker measurements that provide both frequency and modulation insight.
