3.2 Restrictions on Flashing Images and Light

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Do not use a sequence of images that does all of the following.
Flashes so that the change in luminance of the flash exceeds 20 nits (candela/square meter).
Occupies more than one-fourth of the screen.
Has more than three flashes occurring in any 1-second period.
Note:
A "flash" is a pair of opposing changes in luminance: that is, an increase in luminance followed by a decrease or a decrease followed by an increase. If the luminance measurements of successive flashes over time are plotted using x- and y-coordinates (x=time; y=luminance), the shape of the resulting plot appears in profile as alternating peaks (frames of localized maximum brightness) and valleys (frames of localized minimum brightness). Flashes should be evaluated for the change in luminance between adjacent peaks and valleys. No more than three of these peaks (or, alternatively, no more than three valleys) should occur in any 60 consecutive frames.
Screen luminance can be measured or calculated as described in section 3.6 Screen Brightness Calculations.