Will every wave length of UV work for killing bacteria? So will UV A, UV B and UV C all work? Or will only the shortest of the three, UV C, work? Also, will the average UV lamp help against bacterial growth (if it is shone on an object for 3-5 minutes for example)? What about a longer period: a bacterial colony in a petri dish under an average household UV lamp for a day? Would the growth be reduced noticeably? Or would the change be too small to notice when using the average UV lamp? Does the type of UV also matter for this (A/B/C)?
The CDC's disinfection guidelines lists UV radiation between 328 and 210nm as effective for disinfection, with a maximum of bactericidal activity occurring between 240-280nm. At this wavelength DNA damage (Thymine dimers) is induced with a high rate.
Due to practical reasons UV light is mostly used to disinfect water, if used in rooms there is some effectiveness against microorganisms in the air and some on surfaces, but on one hand the effectiveness is reduced by square with the distance from the UV source and on the other hand you need completely empty surfaces where nothing casts shadows. The other problems are plastic materials which may get damaged by repeated UV exposure.
Have a look at this reference (only available via Google Books): "Principles and practices of disinfection, preservation and sterilization." and this subchapter.