red913:
I was going off the datasheet absolute max for current. I thought it said typical. I went back and reviewed it and it's max current is 20mA, not typical current. I measured it and I'm only getting 1mA to a pin and a total of 8mA sourcing the whole LED. Also I was reading a little tutorial on another website and the guy made his calculations on 20mA too. Perhaps that's why I never bothered to measure anything. They're still really bright though.If 20mA is my max and I have 8 pins. 20/8=2.5mA of available current per pin So to be safe I'll stick with 2mA per pin. That works out to a 1K(closest size) resistor and pulling about 17.1mA total from my 5V pin. The next size resistor I have from there is the 2.2K I was using previously. So at this point from I'll stick with the brighter LED's I get off the 1k.
20mA is the recommended maximum per pin with a total recommended maximum for the chip of 200mA.
20mA x 8 = 160mA which while safe for an UNO might be too much for the 7-segment display.
Go with what you can see well enough which is what you're doing anyway.
If you ever do need more power, use a pin through a good bit of resistor to control a transistor that can safely carry the extra. Or use a chip to do the same thing, I've used opto-isolators to control external power use before.
But check out that with motors, solenoids and like (inductive loads) there may be extra circuitry or other chips to use than with for example lots of leds.