Plants DO NOT use the UV part of the light spectrum. Don't get confused because Metal Halides or HPS lights put out some UV light, that plants use this UV light - they do not. In fact Halides and HPS lights put out lots of the light spectrum that plants do not use which makes their use particularly uneconomic because a lot of the light is wasted.
Plants only need/use two parts of the light spectrum - blue 350-500 NW's for vegetative growth and 600-700 NW's for the flowering - neither of these two spectrums contain any UV light whatsoever and the two flavours of Envirolites (compact flourescents) in popular use for growing plants indoors mimic those two colour spectrums in the two bulbs they produce - and neither put out any UV light.
The 'spindly' nature of the plants you describe is entirely due to lack of the correct type of light and lack of quantity of the correct type of light - nothing whatsoever to do with a lack of UV.
And I don't care how old you are or how long you've been growing - plants DO NOT USE UV LIGHT.
Errr... first post here and I hate to disagree, but here's something you might take a look at...
http://findarticles.com/p/articles/mi_qa3931/is_200405/ai_n9446040/
http://www.cazv.cz/2003/PSE3_03/8-zuk.pdf
http://www.jstor.org/pss/1942430
From what I can gather, different parts of the UV spectrum influence different responses in plants, and the effects are further dependant on the particular species... I would imagine looking at the last article that a predominantly Sativa plant would benefit more during the veg phase than an Indica, and vice versa for flowering... a grolux flouro would be suitable for either and wouldn't cost the earth to buy and run.
PS - not been growing weed ever (been smoking it for about 25 years though!), but I do have an MSc in Ecology, which might give me a little bit of a head start - and I advise my mate when he has little problems with his strain of Kush - I'll be telling him to use some UV and will report in a few months
