i dont know about dimming the par bulbs i have only used the 3 watt star bulbs.
what kind of pump ac/dc current. ?
ac can just be turned on off and its hard on the pump, dc you can control the rpm and direction
Yeah, there are differences here you need to specify. I am not aware how PAR38 bulbs can be dimmed. If they are like other LEDs, you need either analog or digital (PWM) dimming signals. Likewise, normally when powerheads like the koralia say they can be used with a controller or wavemaker it is saying they can be used on switching AC outlets, meaning they can be controlled in two states: on and off. In some other cases, analog/digital signals are also sent to control the pumps.