I have an LED lamp that I want to control with my Arduino. It has 6 bright white LEDs (on a PCB) connected to a 6v battery pack. These all appear to be running in series and connected directly to the battery pack with no resistors in sight anywhere which doesn't make a whole lot of sense to me because of the voltage drop between LEDs (assuming 3V) but it works and is bright. Only 2 wires come off the PCB.
My question is, how can I connect and control this with my Arduino Mega 2560. My understanding of the Arduino is that each pin can only output 40ma which is by far short of the required amount if each LED uses 20ma.
Do I have to connect an external power source? If so, how would I go about doing this and could I also power the Arduino with the same power source?
PS. I'm new at all this so please excuse any ignorance.