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T5 HO 53w has 5,000 lumens so 8 tubes be 40,000 lumens on par with and 250w HID setup and cost a lot less
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Comparing lumen output of florescent
lights to HID is like comparing apples to oranges. The biggest difference (besides light wavelength spectrum) is how far from the bulb those lumens can actually go. With florescent lighting that range is very short. That 5,000 lumen rating is only at the bulb, it's drastically lower anything beyond 6 inches to 1 foot. That's not the case with HID. The light intensity of hid reaches much farther (4-5 times). As an example, at about 3 feet from the plant, florescent lighting will have almost no value to the plant. With HID, at the same 3 foot distance the plant will still get 50%-60% of the
bulbs output.
I have only seen one person grow large healthy fruiting plants like cucumbers, melons and tomatoes. If I were to want try growing those kind of plants using florescent, I would do it exactly the same way. Every light fixture was mounted vertical (straight up and down) facing the plant. They were 4 foot long twin bulb fixtures. Now he did modify his light fixtures to overdrive the energy output. But he was also using T8's, but if your using T5's, you'll have roughly the same light output as his overdriven T8's. He placed these light fixtures vertically every 2 feet along the row facing the plants, and on both sides of the rows as well. He had so many of these lights in his basement, it heated his whole house during the winter. Now, given your space of 2ft x 4ft x 6.5ft. To do it the same way it would take 6, 4 foot long twin bulb T5' light fixtures. One in each corner, and one on both sides right in the middle at the 2 foot mark.
Now for costs. I can get 4 foot long twin T5' light fixtures at Home depot for about $40 (bulbs included). $40x6= $240, and that doesn't include the cords and plugs you'll need to wire and plug in the lights. Including tax, electrical cord, and plugs, the lighting setup will cost roughly $300. Those 6 twin bulb fixtures take two 53 watt bulbs each, that's 12, 53 watt bulbs. 12x53= 636 watts being used. I pay 9.3 cents per kilowatt hour, and you can use this
energy cost calculator to run your own numbers.
636 watt florescent lighting (18 hour light period)
Light setup $300
Daily energy cost------------------$1.06
monthly energy cost (30 days)-----$31.80
Even your lower light less effective 8 tube plan would still use 424 watts
Daily energy cost------------------$0.71 a day
monthly energy cost (30 days)-----$21.30
Now using HID for the same space. Two 100 to 150 watt bulbs will give better lighting than the florescent and cost much less.
Two 100 watt HID bulbs
Daily energy cost------------------$0.33
monthly energy cost (30 days)-----$9.90
Two 150 watt HID lights
Daily energy cost------------------$0.50
monthly energy cost (30 days)-----$15.00
That's why I say for my money, I would much rather use HID for large fruiting plants rather than florescent. Any way I look at it, I'd get much better light intensity, and cheaper energy costs. I'm not interested in growing a $6 cucumber when I can get them at the store for 89 cents. Can you grow them using less florescent lighting. Sure but due to low light levels you just wind up with smaller under developed fruit. The less light, the smaller and more under developed they will be.
P.S.
A watt is a measurement of heat energy, and no mater what, a watt of heat is still a watt of heat regardless of the type of bulb. 400 watts of florescent lighting puts out the same amount of heat as a 400 watt HID. Why it seems like it's cooler is because the heat (watt) source is more concentrated in one place with HID. You need multiple bulbs spread over a larger area with florescent, so it's not concentrated in one place. If you go outside on a sunny day the sun feels warm on your skin. But if you take a magnifying glass and focus the light in one spot on your skin, it will begin to burn. It's the same amount of heat, you just concentrated it in one spot. In a space like that 4x2x6 area you should have ventilation anyway. Placing the fan's at the bottom blowing upward will help push the heat out the top as heat rises anyway.