I'd say on average 60 to 70 Watts but it's important to measure the baskingspot temp.
Best way I think to do this is to put something under the baskingspot that's about the same height of the animal, with a neutral color, then let it sit there for 30mins and temp it with an IR temperature gun. If temp is to high elevate the lamp or lower the wattage of the lamp, if temp is to low lower the fixture or try a higher wattage lamp and start over again.
It's a routine you need to repeat every once in a while when redecorating the enclosure but it's a better way of measuring since you measure surface temperature instead of the air temperature you measure with a normal temperature.
Also make sure the lamp is elevated above the mesh so the mesh doesn't become a hotspot and burns your animal, so a higher wattage on a bigger distance may be better than a lower wattage placed on the mesh.