People mostly have the wrong idea about heating brooders. They think it's like baking a cake or cooking a roast, that the brooder has to be of a certain even temperature.
Try to think of chicks being on a camping trip. It's colder than they want, so they need a campfire to warm up. When standing by the fire gets too hot and uncomfortable for them, they move away from it to cool down, returning when they need to warm up again.
The lamp should be hung at a level to produce a temperature of between 85 and 95 degrees on the floor of the brooder under the lamp. All the rest of the brooder should be much cooler. This is just a guideline starting temperature for chicks during the first week, not a hard and fast rule. Raise the lamp next week so the temp is five degrees cooler, then keep lowering the temp until they are weaned off heat by age four or five weeks.