Heat of 12 LED lights 60mA 3.6W PCB
The LED will not turn all the power to heat. Most lighting LEDs have an efficiency of more than 70%. This means, for the worst lighting LEDs, you will turn about 30% of input power to heat. Also, every resistor will dissipate about 0.129W too. This means 12*0.129=1.55W power dissipation on all resistors. Removing this from the input power (3.6W), only about 2W is delivered to LEDs. This means, for a bad LED, you will dissipate about 30%*2W=0.6W power on all 12 LEDs. That and 1.55W dissipation on resistors can warm up a PCB; but for a 0.25W resistor and most LEDs, you will have no problem.