When it comes to fluorescents, longer tubes are better than shorter.

That said, 2 tubes are much better than one.

Hey to get cheaper tubes, check home depot for boxes of 10... I got the 4 foot tubes for $1.70 each that way, they are much more than that at walmart buying 1 or 2 at a time.
I think you should change the bulbs after 1 year, but maybe not if you only use it for part of the year.
The light that they give off is lessened after time, so even if it looks like they are still working they arent giving off as much light... or so ive read.

light falls off as the square of the distance

It falls off real fast.

fluorescents are minimum light to get some growth. Ok for growing seedlings. plants require a long time to harden off slowly and very carefully.

I allow my plant leaves to almost touch or touch the fluorescent bulbs.

I now prefer to carry the plants outdoors and back in over night. the sun really grows them so much better.

Go try this Q in the Hydroponics Forum, you'll get all the info you need.

I agree with sir_lurksalotÂs suggestion, definitely a lot of very knowledgeable folks over on the Hydroponics Forum but, you should also check out the Growing under Lights Forum (link below). ThatÂs where the hard core lights folks hang out LOL.

gardendawgie pointed out a very important law that must be observed when working with light, the Inverse Square Law of Light "the intensity/strength of light is inversely proportional to the square of the distance from the source". To use a plain english example: if your plants require an amount of light equal to what is put off one inch from the bulbs, they will only receive 1/4 the required amount if you move the light source two inches away from the plant.

Personally I start my seedlings off under the cheapest four foot florescent tubes I can find. Once the plants develop their second set of true leafs I transplant into three or four inch pots and move under a 400 watt MH HID (Metal Halid High Intensity Discharge) lamp. I start quite a few plants so I quickly run out of room under the fluorescent. ItÂs a little costly to setup but from a lumen output perspective, itÂs the most economical regarding energy usage. Never really worked it out but IÂve read it in a number of locations from those who have. Anyhow, plants seem happier.

Bill

Here is a link that might be useful: Growing under Lights