Uv bulbs

[gazdkw82]

How often do they need changing?

 

[wellington]

The jury is still out really and depends on the type you are using. The fluorescents, every six months. The MVB, well some say 6 months, some say a year. If you take advantage of the sun when possible, you can extend their usage.

 

[Tom]

The only way to know is to use a UV light meter. I recommend this one:
http://www.solarmeter.com/model65.html