Ultrasonic sensor for art installation

i! I need help with an art installation.
I want to use an ultrasonic sensor to turn on and off 5 leds (the leds turns on as you approach the sensor).

I already have the programming and it works with low power leds but I want to use high power leds and I don´t know how to make the circuit.

My leds are 1w so they need like 300Ma. I want to use external power. 12 volts from a ac/dc converter.

Do you have any idea how the circuit would work with the external power?

Do the LEDs just turn on/off or do they use PWM to modify the brigtness?

If it's the former you'd be fine with any 12v relay: https://www.google.co.uk/search?q=arduino+12v+relay

Or there are transistor circuits that would do the job too.