you will need a lamp when they're first hatched... the light should be low enough for them to huddle under but high enough that they're not panting. Also, there should be enough room in the brooder/coop so that they can get away from the heat. I don't know what the daily temperatures are like but it sounds like it's already too hot during the day. Maybe you only need the light on at night if the temp drops. I know what we do is: when we get the day olds the lamp is only about a foot off the bottom of the coop. Each week we raise the lamp up about an inch. With summer sometimes it goes quicker depending on how the chicks are reacting to the weather outside. Basically, if they're laying with their wings out and panting it's too hot... if they're huddled right under the lamp in a dog pile it's too cold. Hope this helps