Amplifying PWM output

I'd like to use my Arduino to regulate the output of several 12V LEDs, with their own 12V power source. I've tried using a solid state relay (a Vishay VO14642AT) with the Arduino outputting to the relay to switch flow of the 12V power. This works fine for on/off and blinking, but the relay can't amplify PWM dimmed output to run the 12V light at dim. Clearly, this solid state relay won't cut it.

What sort of set-up should I use so that the PWM output will control the brightness of a switched load? Is there a special sort of relay I need? Should I look into a MOSFET driver? Is this what an Op-amp is for?

MOSFET will do this without trouble.

A MOSFET might work, but it depends on the type of "12V LED"... If these are household type lamps that run directly off 12V, they may not be dimmable. Those lamps have circuitry built-in. LEDs by themselves are constant current devices, so you cannot run them directly from a fixed voltage.

Typically with high-power LEDs, you use a switched (PWM controlled) "constant-current" source, and you vary the current to control brightness.

Thanks. The lights are Hyper-Lites, which are designed as auxiliary signal lights for motorcycles. Hyper-Lites controllers have a dimming function, so I'm pretty sure the LEDs can handle PWM. I suspect the lamp is just LEDs and a resistor to drop 12V. I can't see inside the lamp since it is weather-sealed.

I'll try the MOSFET approach. I'm looking at the MCP1406-E/P, or 1407, by Microchip Technology, as it seems suitable and is cheap.

I'll list this as solved, until the MOSFETs blow up into pillars of flame.

Yeah, MOFSET is the best option or if you wanna go hard core, you could get a relay with which you would be able control voltage as high as 120V. With MOFSETS it's usually a 30V Max.