James Newton, Host wrote:
> I've never seen it done, so there is probably a good reason, but why
> not add a capacitor to each LED as a means of expanding the time it is
> on and allowing more current to be pumped in to it without exceeding
> the rating of the LED itself?

LEDs are current devices with current versus voltage "knees", unlike a
resistor which is linear.  In other words, most of the light on to off
occurs over a narrow voltage range, like 1.8 to 2.2 volts for example.  This
means the capacitor must be much larger than otherwise for it to be
effective.  Since you need a capacitor for each individual LED (otherwise it
would not work as storage or defeat the multiplexing causing ghosting), it's
just too cumbersome and expensive to be worth it.  Refreshing the display at
500Hz or so is usually not that big a deal, so that's the easier and cheaper
way out in most cases.


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