Thanks Grumpy. All made sense and I got it working.
A thought though - When using led strip like RGB LED Strip - 60 LED/m - 1m - COM-10259 - SparkFun Electronics Is a constant current driver not the best solution? I've configured a driver circuit to work with a particular length of strip, but now if I want to use a different length, requiring a different current, I'd need to change the value of the current setting resistor. Is this correct?
If so, is this a situation when a constant voltage circuit is more suitable?