[5.9.9.6] Perception of visual unsteadiness induced by a light stimulus, the luminance or spectral distribution of which fluctuates with time, for a static observer in a static environment. (Source: CIE TR 249:2022.)
Note 1: The stimulus can be a light source or an area lit by the light source, generated within the
frequency range of 3 to 80 Hz, for an observer with a steady gaze (on or off-axis). These conditions
maximize the likelihood of seeing direct flicker, but it may be visible also when there is relative motion
or moving objects in the visual field.
Note 2: This definition differs from that of the CIE vocabulary term number 17-22-092 [CIE 2020] in that
it uses the modifier “direct” to distinguish it from the generic term.
