Ive been trying to figure something out.. I have several lamp fixtures with built in dimmers. I like them this way because it keeps things simpler with wiring as upposed to adding a rheostat separately. The one with the 8.5 inch rim holds up to 150 watts, and the one with the 5.5 inch rim holds up to 75 watts. Is this strictly because of the size of the metal reflector or is it also in the wiring / base. I also like these because I can always but the max wattage and dial it down. The reason I ask is because I would like the 5.5 inch I use on a tall exo terra to have a touch more than 75 watts. Obviously safety is of upmost concern so I was wondering if it was okay to just change the shroud. Of course if not I have no problem buying a rheostat separate and a small dome capable of holding 100 watts which seems to be the max for this size fixture. If anyone with technical knowledge in this matter has any input I would greatly appreciate it. I just have numerous fixtures that each have a feature the other one doesn't and was wondering if I could combine for maximum effectiveness. As always any info is greatly appreciated.