PHP not getting new environment variables

I set some new environment variables in my windows machine through CMD and tried running SET, I see my new variables:

FFMPEG=C:\inetpub\wwwroot\ffmpeg.exe

But when I run PHP using exec("set"); I don't see the new variable at all despite restarting IIS. Do I have to reboot the whole machine or is there any way to "refresh" PHP to get the new variables? Thanks in advanced for any help.