The phot r 85w equivalent to 425w fluorescent light bulb is a medium edison screw e27 screw in bulb for the most other floodlight fixtures that can accept a large bulb if you have been trying to shoot pictures with an accurate colour representation of the items you are photographing it is very likely that you have been relying on special filters andor software editing to improve the results with the phot r light bulb this may well be a thing of the past it provides true daylight balanced