Dear Erik,
Thanks for your kind reply,

The reason of asking is the curiosity to know why I do this. I have been using zero cross switching for AC loads weather they were resisitive inductive or any thing in between. While talking to one of my friends he asked why use zero cross switching for resistive loads. I tried to explain him that if fired random the dv/dt or di/dt when switching is done is too high and that causes HF emissions and thats what is radiated noise which ultimately hits the system and causes problems. But I couldnt convince him he asked for any mathematical relation between noise and dv/dt or any theory supporting this phenomena but I couldnt answer.

Thanks & Regards,
Prahlad Purohit