Time to replace MVB bulb?

[BlueMorpho]

Hi,
I bought my first MVB, an ExoTerra SolarGlo, about 8 months ago. I only bought one to test it out for Striker's tank before making the full switch for both my tanks.
I've noticed recently that the MVB isn't putting out much heat anymore. The ballast is still hot to the touch (but cool enough that I can touch it without being burned), and her basking spot is only about 70*F... Last month it was 85*-90*, and because we live in a very warm house and it's fall, she didn't seem bothered by the low temp then. It's still emitting light, but I have no way to test UV levels.
I'm wondering if I can just buy another heat lamp and continue using the SolarGlo for UV, or if I need to replace the bulb entirely.
This was a test run before switching both tanks to MVB, as I go through about 4 tubes/year and about 10 basking lights between my two tanks. It's getting to be about time to replace Eri's UV bulb, too, but since the MVB didn't last as long as I expected, I'm worried that route won't be as cost-effective as I'd hoped.
Thanks in advance!!

 

[CooperDragon]

The output from MVBs degrade over time just as with the UVB tubes so I would replace it. The SolarGlo bulbs are known to decay somewhat rapidly so without having a Solarmeter to test the output I'd err on replacement. Which wattage are you using?

The downside of the MVB is that it produces UVB but you need to mount it at a specific distance based on the output of UVB and it can be difficult to control heat because of that. I prefer to have independent control of UVB and heat in my main tank (I use MVB as a portable basking spot in the living room). I can imagine it was frustrating having to replace the UVB bulbs so frequently. I've found that a T5 will run MUCH longer than a T8 bulb will. My T5 has been running for over 18 months now and still has great output (measured with a Solarmeter). This is what I use http://www.lightyourreptiles.com/22-t-5-ho-fixture-high-output-with-arcadia-d3-12-ho-bulb/

 

[BlueMorpho]

Thanks CooperDragon!
I have a set up for T8, and I'm planning on buying a solar meter in December to help me see if I can reduce costs that way. I found one that's not too expensive, even with shipping.
Unfortunately, the stores near me don't offer Arcadias, just Repti Sun and Repti Glo for tubes, and the only MVB I've found is Solar Glo. I haven't actually seen any T5 bulbs, either, though I'd be willing to switch my setup if I find them next time I look if they really last longer.
The other thing I failed to consider is that the dome lights sit on top of the screen whereas I'd had the linear mounted inside. Her dome lights sit about 11-12" from her basking spot. That will change sometime next summer, when I plan on building some new perches, but I'd like to keep the screen top attached, and the tank's far too shallow to mount such a light inside. ~.~'
Guess I'm sticking with linears. But thanks for the heads-up on the T5s!!