Thanks, I haven't actually got the hardware yet, just trying to lay a pcb out ready, I guess the safest way is to buy some leds and build a breadboard,...

It needs to be LED's as they are to provide illumination.I'd use the zener and a resistor to the LED's from the clamped voltage is easy with ohms law, but...

I want to turn n a number approximately 20 ultrabright LED's from 2 lead acid 12V batteries in series, easy, but I want to maintain the same brightness (current) whatever...