macweenie:
Thanks JimboZA,Although I got a great deal of information before your post, you gave me the piece of the puzzle I was lacking. I hadn't understood just WHERE the current I needed to power, in this case, an LED was coming from.
Glad you understand it.
Now you're getting good a reading datasheets, the second thing you need to look at is the graph of voltage vs. current and the min/max range of voltages that the LED needs. As you'll see the graph shows that ass you approach maximum current, even minor variations in voltage (eg. 0.1V) can produce huge difference differences in current. The LEDs voltage tolerances are often more than 0.1V either way, so what voltage do you aim at...?
This is why controlling LEDs with resistors is a bad idea, and why they make special chips for driving LEDs - you need to control the current, not the voltage.