Why is flicker important – how is it measured?

measuring flicker

The Asensetek Lighting Passport is a full specification lighting spectrometer capable of a wide variety of photometric measurements, including Flicker Index, Percent and Frequency

What is Flicker?

Almost all forms of electric lighting exhibit flicker to some degree.  Poor design in LED drivers and inappropriate choice of dimming controls are among the culprits.  Flicker is somewhat of a subjective phenomenon, with some people being affected more adversely than others. Research indicates that flicker becomes visually noticeable to humans at frequencies below 100 Hz and invisible above 500 Hz. However, both visible and non-visible flicker are of concern. For some, adverse flicker may be little more than a barely perceptible annoyance while for others, debilitating medical conditions can result.  For example, flicker from visible wavelength lamps at frequencies between 3Hz and 70Hz can provoke headaches, migraines, eyestrain, distraction and in severe cases, epileptic seizures. Less well known are issues relating to the strobe effect—which causes objects to appear to be moving at different rates than they truly are; a source of hazard on factory floors.

How is Flicker defined?

IES Flicker Definition

The Illuminating Engineering Society (IES), RP-16-10 standard defines two methods of calculating flicker.  Percent flicker is a relative measure of the cyclic variation in the amplitude of a light source, and flicker index is a measure of the cyclic variation taking into account the shape of the waveform. The following diagram shows a sample waveform and how percent flicker and flicker index are calculated.

How can Flicker be avoided?

A recent Luxreview article offers some excellent advice when sourcing LED drivers and dimming products, however only testing samples using an appropriate instrument can provide quantifiable assurances regarding flicker performance.

The Lighting Passport Pro is one such instrument, which in addition to providing a comprehensive array of photometric data including Lux, CRI and CCT can also measure flicker frequency in the range 5 – 200 Hz in addition to the IES Flicker Index and Flicker Percentage metrics.  For more information or to purchase the Lighting Passport Standard Pro with Flicker measurement visit www.nationalphotonic.com or telephone 01463 711 890