At 39 below zero like yesterday morning I put out three 250 watt bulbs for my 15 chickens. They made use of them.
As far as the difference between infared and heat lamps. beats me. I use the ones my chickens like the best and they gather under the red heat lamps so I put the other clear 250...
I have a drafty old building I use for my coop. It hit 39 below zero outside last night. they're all still living and laying. I do have 3 -250 watt heat lamps for them. Plenty of feed and a heated waterer kept always full.