Is it drafty or cold in the room they are in? That might be causing them to huddle under the light. Try bringing the brooder into a warmer area, and definitely must be draft-free.
If the chicks are huddling under the lamp all the time, they are too cold. They should be ranging around the brooder at different times of the day.
How big is the brooder? if its in a cold room and the box itself is big, then they might be huddling under the lamp because it is the only warm spot available. If the brooder is big, maybe try partitioning it off for a while to help contain heat a little, or add something solid over part of the top for the same purpose. Or if you want to keep it big, maybe add another heat lamp. Or lower the one you already have.
Whatever you do, they should NOT be all huddled under the lamp all the time.
General guide is 90-95 degrees ay "chick level" just to the side of the heat lamp area, and lowering the temp by 5 degrees every week. But the behavior is a better guide.
Drafts are very bad.
Red light bulbs reduce the possibility of the chicks pecking each other. I also think it allows a more natural adjustment to daylight, personally.
Good luck!