wash the chick in warm water and dry it gently, then put back under the light. If it has a lot of poop around the vent, it's called pasty butt and can be DEADLY if not cleaned. Put some warm water on any dried poop to soften it, then clean it off. Be gentle but thorough, and I hope your little guy makes it. Do you have any AviaCharge or electrolytes in the water? Are you using sugar in the water? If not, add some sugar to the water for energy and decrease the amt. of sugar to none over the next few days, and KEEP WATCHING the little one with the poop issue, cleaning as needed.
As for the light, it's needed more for the heat than the light. If the chicks huddle under it, they're cold and you should move the light down a bit. If they stay far away from it, it is too low/hot and should be raised up or directed away from them somewhat. if they're scattered around the box/brooder playing and exploring, they should be just about right. PLEASE check the FAQ section for raising chicks 101. It has a lot of information I'm sure you'll find helpful. Good luck, and welcome to BYC.