That depends upon what you are using for a brooder. Many folks here use small bins or hutches for a few chicks and keep them inside the house, basement, or garage. It is fairly easy to provide enough heat to a few chicks in those types of setups with a regular light bulb.
Traditionally, chicks were brooded inside a ring on the floor of an unheated barn or outbuilding. Those are the conditions where a heat lamp comes in handy. The first chicks we had, I brooded them early in the spring in a ring on the garage floor and used a 250 watt heat lamp. Later batches were brooded on an open-air, screened porch on the back of our house in 50 deg plus weather. The heat lamp worked fine even though it was an open, breezy porch. I just used a high ring to keep the breeze off of the chicks.