Doug101:
Do you know why pull-up and pull-downs are needed?
Yes, to ensure an input is steered high or low respectively when its switch isn't taking it the other way.
So your input where your button is, with a pullup, is normally high, goes low when pressed. You logic says, if the input pin is low (ie pressed), turn the led on some output pin on, else (ie button unpressed, high) turn led off.
The led's on an output pin, so the pullup or pulldown on the button's input pin has nothing to do with the led's brightness.