Think I had my babies to close to light

HI guys and gals, I am wonder what should be the proper distance from the lights to the babies? I have moved 10 of eleven plants to the 400 wt mth and I think I might have had them to close, from reading some other post, but i am not sure. I moved them away from from the light i droped them down about a foot and half. I just noticed that the some of the tips of the leaves are starting to get a little yello kinda looks to me like they were to close what do you think? Oh btw this is my first attempt

Show some pictures. If they are just a little yellow and not full on brown or white spots it isn't light burn.

probably a sign of nute burn. a foot and a half is 18" and you can run a 1kw from that distance if setup right.

easiest way to check if light is damaging your plants is to place your hand right above the plant. if its burning your hand...then its burning the plant.

if height is an issue, your better off removing the hood and letting the light run vertical. this will allow the heat to rise and you can actually get the bulb much closer.