Can you kindly tell me in terms of watts.
There is no power output you can use from L1L2, it is signal only. To drive your LEDs you need a dedicated LED driver. To dim the LEDs, it has to be able to work with 1-10V signal. In any case you need an external power supply.

Have in mind: 6x 3Watts are 18 watt which mean 1,5 ampere at 12 volt.