humidity in prop tray?

im about to germ my seeds in a prop tray that has a humidity dome with two adjustable vents at the top of the dome. and i was wondering how much humidity do i want in the dome while my seeds are germing up untile they are big enough to transplant? do i leave the vents closed at all times so the humidity is really high or do i want the vents open to keep it low? i was planning on putting the proptray and dome under a heating pad on low so im sure that will add some humidity?

45-65 % is perfect for seedlings and sprouters.
top right, growfaq, will help you on more of these very, very simple questions. growing may involve some research.