Canon EOS 80D - Manual (Page 180)

3 Reducing FlickerN
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 If the subject is against a dark background or if there is a bright light in
the image, flicker may not be properly detected.
 Under certain special types of lighting, the camera may not be able to
reduce the effects of the flicker even when is displayed in the
viewfinder.
 Depending on the light source, flicker may not be detected properly.
 If you recompose a shot, may appear and disappear
intermittently.
 Depending on the light sources or shooting conditions, expected result
may not be obtained even if you use this function.
 Taking test shots in advance is recommended.
 If is not displayed in the viewfinder, under [52: Viewfinder
display], set [Flicker detection] to [Show] (p.74). When the camera
reduces the effects of the flicker when you shoot, will light
up. Under a light source which does not flicker, or if no flicker is detected,
will not be displayed.
 If [Flicker detection] is set to [Show] and [Anti-flicker shoot.] is set to
[Disable], metering under a flickering light source will cause
to blink in the viewfinder as a warning. Setting [Enable] before shooting
is recommended.
 In Basic Zone modes, will not be displayed, but the effects of
flicker will be reduced when you shoot.
 Anti-flicker shooting also works with flash. However, the expected result
may not be obtained during wireless flash shooting.