plant growth comes from the visible light NOT UV therefore UV would have no effect. plants outside are exposed to uv light but again has no effect. as to killing microbes some are benificial & would not wish to kill them...

ksrogers, you have basically reiterated and confirmed everything I already said in my previous two posts. For purposes of this forum and this thread I was merely pointing out that plants do not use UV light for photosynthesis. You made several mistatements regarding UV light and I was merely correcting those. You said there were visible and invisible UV, I was correcting that statement: there is only one meaning that UV is invisible. I didn't mean that there weren't other types of UV light (UVA, UVB, UVC). I apologize if you thought I was questioning your methods. I've been doing this long enough to know that there are many ways to grow healthy, vigorous plants. This is how I do it and how my father did it before me (he wrote an award winning book on herb propagation and I learned from him): Although I grow 100,000 plants a year (approx. 60,000 from seed the rest from cuttings and purchased plugs), the methods were devoloped when my father was producing far fewer plants. My seedlings are started under florescent tubes. I use a lot of them-four, eight foot long fixtures with two 60 watt, cool white lamps per fixture, per shelf. This accomodates eight flats per shelf (I have 15 shelves). The lights are set about 2 to 4 inches above the seedlings for 14 hours a day. For me, grow lights would be too expensive and unnecessary. There were studies done many years ago that showed that cool white florescents were as good or better than standard grow lights for starting seeds. You are corrrect that the lights lose their effectiveness as you move them away from plants so they wouldn't be used to grow plants on to maturity. When the seedlings are transplanted into pots, they go in a heated greenhouse-30 X 60. When the greenhouse bench space is full, I grow under the benches using 400 watt high pressure sodium Agro sun lamps that have more blue in their output than standard HPS lamps. To clarify, I use HAF fans for circulation. When it is warm enough, both sides open their entire length (creating a 4 foot wide opening 60 feet long) and the roof vent opens to allow the hot air to escape. The open vents create their own circulation-as hot air escapes from the top cooler air rushes in the sides to replace it. Other commercial growers use large fans on the end of the greenhouse to draw air through the entire house. Yes mercury vapor puts out UV. However, some (if not all) lamps have a coating inside to prevent their escape and to convert much of the UV to a more useful (and less harmful) wavelength in the visible spectrum. The link you provided is to a light fixture that uses both HPS (high pressure sodium) and metal halide lamps (similar in technology to mercury vapor) in them to take advantage of their light output in the different ends of the visible light spectrum. Metal halide is generally used when there is no natural light, HPS when the natural light is being supplemented ie to extend the long days of winter. They are used this way because of the spectrum of light emitted from them. When my fixtures where purchased (25 years ago) MH technology was not as good as it is today and lamps (bulbs) had a tendency to explode in damp environments like a greenhouse among other drawbacks. In some ways I wish I had MH lamps to take advantage of the blue spectrum but replacing 30 or so fixtures and lamps is cost prohibitive which is why I use the special blue spectrum HPS lamps now.

Cuffs, great and helpful info. Based on what you said,I would guess the improvement in your air situation is due more to the media filter than the UV light, because the mold/mildew you had previously was not coming crom AC system (since the house did not have one before). The UV light is designed (from what i've learned in last few days) to prevent or kill mold growth on the AC condenser coils. Looked at some adevertisements for filters and an 11 MERV filter will catch mold spores and pollen, among other things. Your filter is probably much higher than 11. An article in Consumer Reports sometime in the last 1-2 years says (simplifying a bit) a high-end 1 inch pleated filter is almost as efficient (at removing stuff from the air) as electrostatic or those 5-inch media systems. Sounds like the Air Bear is good and most practical approach. It is a bit better than a high-end pleated filtr, but is not terribly expensive to install. If I had alergies, would replace/clean that filter frequently. I will wait to see some impartial scientific data on UV lights in residential systems. Apparantly, the ones they use in hospitals and other commenrcial buildings have different specifications and have other purposes like killing bacteria. The "studies" or info put out now seem, in my opinion to be self-serving on unconvincing at the least. Thanks for all the help

It looks like my thanks didn't get posted. thank you for the reply. I'm trying to locate the lamp now. --hadn't thought of ebay. Hope they have a new one, since these are only good for 1 yr. I'll check with fielcontrols too. This is very helpful.