PaulRB:
Multiplexing will reduce the average current... apparent brightness.My reason for recommending common anode is that this enables you to use the tpic6c595 shift registers I was describing.
Sorry for the confusion. History: I made a sign (scoreboard) that has 15 large displays. Each 7 segment digit is made up of an average 7 leds in series (with a 330 ohm resistor each) x 8 rows in parallel. I'm currently running each LED somewhere between 12 to 15mA only in full daylight (given these are fairly bright units). The total current draw per segment ends up either 120mA or 780mA. These are being driven by discrete components - the leds via ULN2003's. LED forward voltage is 2.7V. Overall, max of 11.7Amps to run all digits if displaying "8" on each.
Now that I've found "Arduino", I've fallen in love! I want to convert it to programming. I will have to change the drivers, but I'm just trying to work out the "easiest" way for me to do the programming, use existing Arduino boards with whatever drivers I need. But before that, I need to look at basics - yes as you said the display will be dimmer with multiplexing.
At this stage my idea is to drive only 4 of the digits with one Arduino Uno board, mulitiplexing only 4 digits. This will 1/4 the intensity I think, if I give the same current (i.e. end result of 12 to 15mA each LED). However, I "think" I can increase the current to 4 times as much (48 to 60mA?) as they are only on a quarter of the time. Is this correct? Would this give the same intensity?
Then comes the dimming during night time. Is my suggestion of an LDR the way to go?