Will I need external power? How to calculate it?

Ok thank you.

Please help me understanding this:

Lets say I want to connect some simple leds like these:

http://www.ebay.com/itm/100pcs-Purple-5mm-2000mcd-Lamp-Ultra-LED-Free-Shipping-UV-/110980369904?pt=LH_DefaultDomain_0&hash=item19d6f20df0

specs says: Max Peak Forward Current : 75mA

Does this means that with 6 or 7 leds I would be reaching the limit of the board?
Also the Mega documentation says each port delivers only 40ma so I don't get it.