flickerindex

Flickerindex is a term used in lighting, imaging, and display contexts to describe the degree of temporal brightness variation, i.e., flicker, in a signal or source. There is no single universally accepted definition; different communities adopt related measures that quantify how much the luminance or intensity deviates over time from its mean. In practice, flicker index can be computed from time series of luminance L(t) collected at a rate high enough to resolve flicker.

One common approach in lighting engineering is to normalize the instantaneous luminance by its mean and aggregate the deviations over a cycle. A discrete form is FI = (1/(N-1)) sum_{t=1}^{N-1} |L_{t+1} - L_t| / L_mean, where N is the number of samples in the window. An alternative form uses the root-mean-square deviation: FI_rms = sqrt( (1/N) sum (L_t - L_mean)^2 ) / L_mean. In other contexts, flicker strength is also expressed as an amplitude modulation index M = (Imax - Imin)/(Imax + Imin), which is closely related to the notion of flicker severity.

Measurement typically requires a calibrated photodetector or luminance sensor and a data acquisition system with a sampling rate well above the flicker frequency. Calculations are performed over a defined observation window, such as one or several cycles of the source.

Applications include specification and comparison of light sources, drivers, and lighting control systems; assessment of perceptual flicker risk; and quality control in displays and imaging equipment. Standards bodies and researchers use flicker metrics, including flicker index variations, to guide design and compliance processes.