I don't think you can get 100w red bulbs at farm stores, but if you get a higher watt bulb, you can either put the bulb on a dimmer, or raise it. I'd try to get a 125w red bulb, if you can find one. The more standard size is 250w, but if a 100w bulb keeps your brooder at 95 degrees, you might not need that big of a bulb (larger bulbs use more electricity, too). I wonder do reptile bulbs come in lower wattages? That might be what you could use, but they might be more expensive than a normal red bulb from a farm store.
I don't think red bulbs give off less heat than white ones, but maybe I'm completely wrong.
Maybe someone wiser than me in chicken-raising will join this thread and give you better help. This is only our first batch of chicks, and we've still got plenty to learn.
BTW we use a 250w red bulb on a dimmer, but our brooder might be bigger than yours.