Undercover, what is the dimesions of your 8 bulb? Is it the same as it says on ebay. They say the 8 bulb is 4' x 16.75in and the 4 bulb is 4' x 13in. my badboy 8 bulb is 4' x 2' and my hydrofarm 6 bulb is 4' x 18in. Out of all the radiion ones on ebay, for more light coverage getting a couple 4 bulbs would be the best way to go.... right...?
Yeah those dimensions are about right. They are pretty compact units, only 2-3 inches high also. The 8 bulb unit is almost the same as the 4 bulb, but the reflectors are a little wider and they put 2 bulbs in each, so they are a little less efficient due to re-strike as the tubes shine on each other within the reflector. I would say the 4 bulb units would be a little more efficient due to the individual reflectors and wider spaced bulbs giving better coverage. They dont get hot at all where as the 8 bulb units do get a little hot, but not where my tops arent 2-3" away.
Overall, if you're strapped for $, the 8 bulb units are an awesome deal at $150 (the aquarium version can come with 50/50 or all Actinic460 which look exactly like the WavePoint Blue Waves when next to each other... so you can save money on bulbs also).
But IMO, if I had $300 budgeted for fixtures, I would get 3 four bulb units over 2 eight bulb units. Although you'd get 4 less bulbs and their light, I think the benefits of the better coverage/spread from the wider/individual reflectors, and the fact that you're saving 216w, 12bulbs=648wfor almost 40" x 48" coverage vs 16bulb=864 for only 34"x48" coverage. Plus you can adjust each of the 3 smaller fixtures individually to fit plants easier than 2 larger.
This is just my opinion, and have never flowered solo w T5's (mixed w Hps) but through veg the 4 bulbs are great. For flowering, I cant say if the overall loss of those lumens/watts would drastically affect yield much, but I know that plants love having the T5's really close, and the 8 bulb units are a little heavier and not as easy to adjust right down onto the tops. I'd go all 4 bulb units if I could just for adjustability, but the 8 bulb units fix perfectly in my veg box and covered my bubblers perfect so i got one
I know some like having two bulbs per reflector to blend the spectrums... but its not as effiecient because alot of the light energy is lost when the bulbs shine on each other and not a reflector.
From pics Ive seen, I think the Radiions are just clones of the Sunburst units.