It totally depends how far above the floor the lamp is and what the room's air temperature is. It is good to have several bulbs available at different wattages so you have the flexibility to do whatcha need to do.
As far as how far above the floor the lamp is hung -- you want to keep a high-wattage heat lamp at least 18" above the bedding; lower wattage things like 100w floodlamp bulbs can go a bit closer if necessary. Also the more chicks you have, either you need the lamp higher so the circle of warmth is larger or you need multiple lamps -- basically you have to make sure there is sufficient warm area for all the chicks.
FWIW, in a 52-55 F basement I start with a 250w bulb about 18" above the floor for up to 20+ chicks, and fairly soon can reduce it to a 175 hung a little lower. (After 1.5-2 wks I put them into the chicken bldg under a lamp-heated plywood hover, so bulb wattages become less comparable at that point)
It is a good idea to get it ballpark correct before the chicks will be going in -- either put a thermometer on the bedding under the lamp, or at least aim for having some area (but not the whole brooder!!) warm enough that if you put your hand there at 'chick level' it gets uncomfortably warm after 30-60 seconds. Then once the chicks go in, you can observe their behavior and adjust accordingly.
Good luck, have fun,
Pat