I could be wrong, but when working with 7-seg LED display in
multiplexing mode, looks like that near the flickering frequency the
LEDs are brighter than when using a multiplexing higher frequency.

Wagner

William Chops Westfield wrote:
>
>     >     Talbot's law. Named after the English physicist and photographer,
>     > William Henry Fox Talbot (1800-1877), who discovered that when the
>     > cycle of a flickering light reaches so high a rate that it perceived
>     > as being continuous, its apparent brightness is equal to the mean of
>     > the brightness of the complete flicker cycle.  Also known as the
>     > Talbot-Plateau law, after Talbot     and the Belgian physicist Joseph
>     > Antoine Ferdinand Plateau (1801-1883).
>
>       What you perceive is the average for frequencies above teh "flicker"
>     or "fusion" frequency.
>
> Whereas others have said that apparent brightness is based on peak
> brightness, for a flashing LED.
>
> If both are correct, then a blinking LED at a particular pulse width
> (percentage) should suddenly appear to get dimmer when you exceed the
> flicker frequency...  Has anybody acctually observed this?
>
> BillW