We use radiant heaters in our brooder house, It is a lot like the one from Lee Valley Sue talks about (I think). The one we have is called a Q ray. We use it to heat the entire building (About 12X14'), that way the chicks are warm no matter where they go.
We have a smaller one we picked up at Princess Auto, we use it for the small brooder (5X7') and it works good. We have both on thermostats around ground level so it detects the temperature where the chicks are at.
I think when you heat a building it creates a better start for the chicks, of course right under the heater is warmer than to the edges, but they can find where they are happy and not have to huddle around heat lamps, making happier chicks in my opinion.