Welcome to indoor gardening slimak! I only started indoor gardening last year with T5 lights so my results may not be totally typical.

If you plan to grow veggies to harvest I personally don't believe you can have too many T5 lights. In a 4X4 area I have 16 bulbs overhead.

Regarding the reflectors I found using the reflectors that came with sunblaster or pro light produced just about 2x as many lumens as ordinary fixtures. This test could also be skewed slightly as the sample is very low. I took one 2 bulb fixture to the local nursery and tested it against their 2 bulb fixtures.

I can only comment on bulb performance regarding seedlings. This winter I will try crops under different bulbs to see how harvest differs. In my experience the bulbs rated (online research) with a higher par value had my plants lean in that direction. I was able to test 6 different types of bulbs. In the end, the full spectrum bulbs seemed to be the best over cool or warm lights, granted PAR value was lower on all other bulbs.

While the cost of T5 fixtures is dropping at the time when I bought my lights I found that the multiple bulb fixtures were cheaper than individual "shop" lights, even at contractor pricing, especially when you factor in time and supplies to link multiple units. I ended up buying two 8 bulb 4' pro light fixtures and 2 single 4' fixtures I use for side light on tall plants.

Hope this is of some help.

Thank you for your answer SCG, however I need to find out I would like to find out what would be a minimum amount of 4 foot T5HOs to get the job done. I'm new at this but I believe that if you put too many lights it would not be the plants nor my wallet :) I'm just trying to figure out what type of fixture I need for it to work efficiently.

I still have to learn about light intensity and PAR to understand it a little better and what brand bulbs to get.

Eventually I would like to try the LED lights but from what I see the units that would actually work, with lenses, are a little expensive :) Penetrator X looks nice.

Having lights mounted vertically makes sense but is it really necessary if you have a grow tent with reflective walls?

slimak,
If you want to save money start by growing your plants in a sunny window. Then move up to a couple of lights.

Efficiency in lights equates to the PAR it produces...more lights=higher PAR

If I was you I would grow all my plants under one light.. then if it didn't work out go to two....then three..etc..

In the end you can get away with anything...but at what cost?

It all depends on your budget. You can always spend unlimited amounts of $$ even to light something as small as 4x4. If you're going to go with T5, try a VHO! The extra wattage is worth the little difference in cost.

I went from an old T12 to the T5 I use now and it does make a big difference. But, I use my 1000W H.I.D. lighting when I want my plants to grow as if they're outdoors. The risk of fire is low if you hang it properly and the plants growth response is 10 times greater compared to a T5.