Help How far should My plant be if Im using 250 watt

Im wondering how far my plant should be away from the light if im using a 250 watt. how much flowering can I get with this type of watt

i just uses the hand method put your hand under your light at the top of your plant and hold it there for awhile if it feels really hot or uncomfortable after awhile then chances are your plants wont like it and jus keep in mind those lights will be on for at least 18hrs for awhile so its gona get hot