I have a friend that hits 1.7~1.9 regularly with 600's in a vert garden
Oh well dont use LED then, Use that lol
Unless the veg Time is like 3 months then youre still loosing over the course of a year.
Can you link to his grow?
Well the trick there is that HPS fixtures lose a lot of light on the reflector and on the walls.
They tested the Gavita Pro fixtures and those tests indicate that already 18% of the light will be lost on the reflector.
Also, the HPS fixtures are usually designed to be placed in large green houses. They have beam angles of 140 degrees and a large distance to the canopy. In small grows this means that reflectivity of the walls becomes a very important factor, but this is also a very underrated thing in grow rooms. Mostly it's just a flat while wall with 60% diffuse reflectivity.
With a
vertical HPS grow the reflector losses are eliminated and the wall losses are reduced. Therefore the yield per watt goes up since you have at least 25% more light on the plants from the same bulb. If you had a very poorly reflective grow room when using top lighting you would gain even more from going vertical.
Another thing is that the lighted surface area gets bigger. A 4 feet tall cylinder with 2 feet radius around a 600W bulb has a much larger surface area than the usual 4'x4' grow surface. The light is thus distributed over a much larger area and the resulting light intensity is probably only about 400umol/s/m2. Which will indeed produce a higher g/W ratio, but it also means the results with these types of grows tend to look fluffy. I have seen some of the vert grows going even over 2g/W (Like Heath Robinsons grow:
https://www.rollitup.org/t/heaths-flooded-tube-vertical.149998/), but the harvest looked extremely "leafy" and fluffy.
For COB grows there is not real gain in yield from going vertical since there are no reflector losses (unless you insist on using them) and the wall losses are already quite low. With COBs you don't get a lighted cylinder either. The COB just lights up the same circular area but then vertical.