Flicker index
Flicker index — waveform-shape-aware flicker metric
Definition
Flicker index is a unitless number from 0 to 1 that captures both the amplitude and the waveform shape of light modulation. It is the area of the waveform above the mean divided by the total area under the waveform, computed over one modulation cycle. Higher = worse flicker.
Source overview
Flicker index is defined as the area of the modulation waveform that lies above its mean value, divided by the total area under the waveform, taken over one full modulation cycle. The result is a unitless ratio between 0 (no flicker) and a theoretical maximum of 0.5 for a symmetric square wave at 50% duty. It is more discriminating than percent flicker because it accounts for waveform asymmetry — short bright pulses score higher than continuous sinusoids of the same amplitude.
The underlying standard is paywalled or otherwise not directly reproducible here. The text above is a plain-language summary written by Slick Engineering — not a verbatim quote. Authoritative source linked below.
Technical detail
Flicker index complements rather than replaces percent flicker. A 50%-duty square wave at 30% modulation depth has the same percent flicker as a sinusoid at 30%, but a noticeably higher flicker index because the square wave concentrates its energy at the modulation frequency rather than distributing it.
Flicker index does NOT incorporate human visual perception weighting — it is a geometric property of the waveform. PstLM (IEC TR 61547-1:2015) is the equivalent perceptually-weighted metric.
Where it appears
- FlickerSpec Used here
Reported on every measurement alongside percent flicker. Useful for distinguishing waveform shapes that percent flicker alone would call equivalent.
Related terms
- Percent flicker
Percent flicker is the relative variation in light output of a source over one full modulation cycle, expressed as a percentage. 0% means no…
- IEEE 1789-2015
IEEE 1789-2015 is an IEEE recommended practice that defines low-risk and no-effect frequency / modulation-depth thresholds for current modul…
- PstLM
PstLM is a single-scalar perceptual metric for how annoying flicker from a light source is to a static human observer. PstLM = 1.0 correspon…