the color of the fixture... LOL... and i think they might be heavier since the ballast is inside the fixtures most of the time... but, hydroponics is a slightly more elite hobby... or industrial'esque... so, everything is more heavy duty built to last... not built to look good, yet not rust... LOL...
not if you do hydroponics the way it was intended... to grow vegetables and chili pepper plants indoors....
LOL...
i gro orchids hydroponically... but i use a lot of nutrients for my chili plants... and orchids...