> So, a big question I have now is, how many individual LEDs can
> you multiplex so that the display is bright enough?  What is the
> minimum number of components needed to drive 100's multiplexed
> LEDs?

A work in progress

http://home.clear.net.nz/pages/joecolquitt/message.html

The LEDs are 3mm HLMP-1385, which are pretty bright at only
1mA, so components used here are well within heat and current
specs. When running, because of the duty cycle at 200Hz, the
whole thing uses under 40mA. More suitable for indoor applications,
but even super-brights wash out to some extent in strong sunlight.
Each individual LED in that display is addressable meaning that
it is (or will be) capable of more than simple scrolling

I've worked on commercial displays using super-brights. One or
two were quite on the edge spec-wise and in fact were in need
of beefing up to keep them going reliably. One I remember ran
on a 12V rail with (seriously under-rated) 33 ohm resistors where
I have my 270R. Those that hadn't burned out weren't long for this
world and were replaced with 2W rather than the 1/2W factory
issue. The drivers ISTR were ULN2003 Darlington ICs. The PSU
was very noisy, hum and spikes all over de place, which didn't
help clean switching. LEDs which were supposed to be completely
off still had a glow, particularly noticeable at night. A few chokes
and caps on the 12V rail plus pulldowns on the driver bases fixed
that up, a vast improvement, something that would have been done
easily at manufacture

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