I want to be able to turn on 50 red LEDs with one pin of an Arduino. I don't want individual control, I just want to be able to turn them all on or all off.

I found [this example](http://www.ecs.umass.edu/ece/m5/tutorials/multiple_LEDs_tutorial.html). It uses a 2N3904 transistor. Is this the approach I want to take? I presume I would need a higher power transistor?

I am using an external power supply that is wired into a custom board with a 5v voltage regulator so I am powering the LEDs directly from this regulator. 

The LEDs come in the form of [this LED light bar array](http://uk.farnell.com/kingbright/dc-10surkwa/bargraph-array-10-segment-red/dp/2079882) (or at least very similar)... 

I had mentioned in a comment in an answer below that I was using a 330 ohm resistor with each LED. On another part of this project, I use the light bars as level meters, and each separate LED is controlled via a shift register, thus the separate resistor. I realise after thinking about it that I don't need to have a resistor in series with each LED for this now as they are either all on or all off (hmmm.... sorry for my rather haphazard comments!).

I did have a thought that I could have some sort of electronic switch that can disconnect ground or 5V. Is this viable?