I recently switched our powersun 100 watt bulb to a exo terra 75 watt bulb in hopes of bringing down the tempurare.
It didn't lower the temperature at all, I have the lamp raised to the highest level it can go on the stand as well which is about 16 inches above the basking spot.
So we went back to the store today and bought a 50 watt zoo med basking bulb and the tempurature increased instead of lowering.
Im wondering if these bulbs just burn hotter for the first bit when you get them, or what is going on?
You can easily remedy this by adding a lamp dimmer to your fixture. Just lower the dimmer switch until desired temp is achieved. I have dimmers on all my heating lights. Room temps can greatly effect tank temps, and this is an easy way to adjust them accordingly. Make sure you use a probe or temp gun on the basking spot to check the temp correctly.
The dimmer will work with the ZooMed bulbs but it shouldn't be used with the PowerSun or a MVB because it may cause problems with the ballast. I would also keep the 100w PowerSun at 8-12'' for optimal UVB output. Closer than that could be harmful and further it may not produce adequate UVB over the basking area. If it's providing too much heat it may be best to use a separate tube style UVB light and heat source as you've done. The 50w ZooMed basking lamp shouldn't be putting out a ton of heat at distance. They do have a bit of burn in time from what I've seen but if you set it 12+'' above the basking area it should be adequate. Perhaps the enclosure needs increased ventilation. You could also try a low wattage halogen flood light. These work pretty well for heat and are easy to dim (I have one on a dimming thermostat).
I don't have the mvb as a light source anymore, we got the zoomed 50 watt to replace that and also have a reptisun 10.0 tube uvb light. And I have 2 probe thermometers on each end of his tank.
We just strung the new 50 watt bulb up higher for now and have put a fan on the tank.
I will be looking at getting dimmer asap, thank you both again for the advice