My understanding is that those dimmer switches still burn the same amount of electricity, just cut the amount of heat/light going through the bulb. Better IMO to use a bulb of less wattage, or perhaps a ceramic heat emitter from the reptile section at the pet store. You only need a very small foot print of space in your brooder for the chicks to warm up. That tiny space should be no more than 90 - 95* the first couple of days. After that, it should be only warm enough to keep the chicks content, and be turned off for increasingly longer periods of time until they have no supplemental heat at 3 weeks, if they are being brooded in the house. By 3 weeks of age, the chicks should have 2 s.f. of open brooder space per bird.
However, IMO, the gold standard is the MHP system which uses a heating pad over a wire frame. @Blooie has 2 articles and a thread dedicated to this concept. MHP is much safer, more natural, and is not a risk of overheating. Many chicks are killed each year from being overheated by heat lamps. If your brooder is not big enough so that the far end of the brooder is ROOM TEMPERATURE, you have too much heat in that brooder!!
However, IMO, the gold standard is the MHP system which uses a heating pad over a wire frame. @Blooie has 2 articles and a thread dedicated to this concept. MHP is much safer, more natural, and is not a risk of overheating. Many chicks are killed each year from being overheated by heat lamps. If your brooder is not big enough so that the far end of the brooder is ROOM TEMPERATURE, you have too much heat in that brooder!!