ok.. Read through the article and I might be able to expand on it in terms we use a bit more often.
I am using one of my 2600K
bulbs as an example in this.
My bulbs use about 32W and provide 2475 lumens. I pulled up a few calculators, and that comes out to about 230 foot candles (x4 for 4 ft) equalls 920 ft candles.
My bulbs are obviously more efficient than the ones that they use in the example. The one in the example provides about 20 ftcandles per W and mine about 28 per watt.
So, needing 40 W per ft for tomatoes with their bulbs would mean to those using 77 lumen per watt bulb (compared to their 58) could use around 30W per ft. So you would only need 3 tubes running instead of 4. That being said I think the configuration of your light will make a huge difference.
If you are hanging your
lights above the tomato plant I think you should stick with the 4 or more bulbs... If you are running your lights up the length of the plant you might just be able to get away with 3 T8 bulbs.
This is in no way a proven fact. Though I have seen people grow tomatoes with a lot less light than most people use, by having their lights run the length of the plant rather than shine down on it. Running the light virtically lets you maximize the light use rather than the light being almost worthless to the plant by time it hits the bottom leaves, or reflects off of something else to get to them. Light from flourescents loses about 1/4 of it's strength per foot, past the first foot. I hope my thoughts on the artical are useful to some :P This was more of a think it out post than a already had it all written down and practiced and known. and I hope that I was able to help someone atleast think about their flourescents a bit to try to find a more efficient use of them.