I’m using transistors to ground each group of LEDs, so a field of 30 transistors was needed. The transistors being used are 2N4401s. The collector of each transistor is connected to ground, the base to the arduino, and the emitter to the LED group (via a 39 ohm resistor).
I decided to put the transistors on veroboard, rather than PCB, as veroboard is much easier to use, and is laid out in a simpler way. I put 5 transistors on each row, so 6 rows in total.
I then soldered jumper cables to the grounds, and wires to the base and emitter (via a 39 ohm resistor). I made the decision to use terminal blocks to connect the circuit-board to the LED wires, so that both units can be easily separated if necessary.