dhenry:
You do realize that that particular kit is not a constant current driver, right? However, if you add a small npn + a resistor to it, you can easily make it into a constant current drive.
Yes I realized that it was not a constant-current driver but had that available and thought of trying it with the benchtop power supply (ISO-TECH DC Power Supply IPS 3303S, http://radionics.rs-online.com/web/p/bench-power-supplies/6842998/). Do you think there is a more elegant way to switch the output from constant current supply such as those from benchtop lab power supply or from commercial LED drivers
[edit] The basic circuit that I know just sets up the current with the R3 resistor (http://www.instructables.com/id/Power-LED-s---simplest-light-with-constant-current/step2/Specs-Function/) but as I would already have the constant current source, I would like to tinker the circuit so that I could add the switching stage.