Mercury vapor question

[Koopatroopa1122]

Just upgraded to a 75 gallon tank we got for free to get us until we move abd I build a custom one. I've rigged up a cover to mount lights and was going to have a 18 inch tube on one side and use a Mercury vapor for the basking side. Question is what wattage should I use for about 15 inches off the bottom and probably 10 to 12 from the the hot spot on his log? Will a 100 be enough? They're expensive and id hate to have to buy multiples to test out

 

[CooperDragon]

Are you looking at using a T8 tube for UVB? At that distance you might be best off using a T5 tube for UVB and then get a halogen flood light for basking so you can use a dimmer or dimming thermostat to fine tune the output. I like using the tube style UVB lights for the main enclosure because of the nice wide, even beam they produce and also since I can set it at an appropriate distance and then adjust heat separately.

If you do go with a MVB, at 10-12'' a 100w PowerSun should do the trick in terms of UVB output.

 

[Koopatroopa1122]

I am more questioning the heat output to act as a basking bulb as well.

 

[CooperDragon]

That's the rub with a MVB. You have to set them at an appropriate distance for UVB output which for a 100w PowerSun is around 10-12'' or so. They don't always produce a proper heat gradient at that distance (and it varies by brand).