Thanks for your replies guys, much appreciated.
Wow, Mojo – how cool is that LED calculator - thanks!!!!
After plugging in various combinations of source voltage values, I decided to use a spare 24Vdc 1A regulated mains adapter, which gave me the attached series circuit.
A bit of Googling seemed to turn up the advice that it was preferable to connect LEDs in Series rather than Parallel.
There is hope for Ponders and myself yet!
Cheers
Dennis