These are the LED's
http://www.ebay.co.uk/itm/270838073318?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
I understand that by using the pot im controlling the overall current available to all of the LED's so when the number of lit LED's changes the current available will increase/decrease and affect the brightness of the remaining lit LED's
Will using the FET not be essentially the same as varying the voltage to the FET controls the current through it?
EDIT: I probably should have said that the project is one of those word clocks, so the number of lit LED's will vary depending on the time being displayed. I'm looking for a way to control the brightness which will stay constant no matter how many LED's are lit.