Matt: As trial try operating the 24 volt lights from 12 volts; you could get the 12 volts from a battery charger which puts out 4 amps at approx. 12 volts DC. Or even for trial from the car battery. Each light will probably dim to something around one quarter (or less) brightness). Another way could be to put the four 24 volt lights in two pairs in series across the 24 volts, thus halving the voltage across each bulb, again obtaining approximately one quarter brightness. If that's satisfactory you could either leave the lights permanently wired up in pairs (dimmed all the time) or put in some switches for, A) Full bright B) Dimmed. using a small battery charger battery, a single switch could switch over from 24 volts AC to 12 volts DC. Again it is not continuously variable dimming; but only one stage. I'm sure that a capable amateur could design and build a suitable and continuous dimmer. I can think of a couple of ways of using a voltage bucking transformer, say. But do I understand that you want to dim the four lights without affecting; and this I'm not clear about, either a 230 or 24 volts supply to the pond equipment? Any help? Terry.