cam break in valve spring pressure

I have been doing some searches on here and can't seem to find a good rule of thumb for exactly how much spring pressure should be used for cam break in. I am guessing 2/3 or 3/4 of normal recommended spring pressure? I just removed my innner springs, but a friend is breaking in a cam and will be using single springs. I have some lighter springs he could use for break in, but how light do they need to be?