A 1000W 42% efficient prefab COB lamp ($2200) will crush a 42% efficient 1000W DE ($500) in yield, but clearly not in up front cost. Hopefully that answers your question OP.
We don't normally recommend 1000W of COB in a 4X4 because that would result in 23.6 PAR W/ft² or
1180 PPFD averaged, with some hot spots at or above 1500PPFD most likely. I run with about 650W of COB in each 4.5X4.5 or about 750 PPFD averaged. Nug size is right where I want it. Yield 1.5 to 1.9 unts for mid yielders, top shelf, in soil. Yield is important to me but
quality comes first.
Here are some decent yielding ladies that did not make the cut due to inferior quality. The lady on the right, Purple Chem was a keeper but not a great yielder.
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A brand new bulb/reflector 1000 HPS DE in a 4X4 results in 20 PAR W/ft² or
990 PPFD averaged, still a bit higher than I prefer, more uneven spread, lopsided spectral distribution and an 825nm infrared heat spike, resulting in warmer canopy temps. Higher canopy temps will increase photosynthesis and weight on the scale, somewhat making up for the reflector losses, but will it increase cannabinoids and terpenes as well? That is the end goal after all.
HID heavily depends on reflectors because the output is in a 360 degree globe. The reflector cannot be cleaned and loses efficiency over time. Jair from Gavita recommends replacing the reflector along with the bulb to maintain output.
Overall, it is clear that 1000W DE is a much lower up front cost. But that advantage is reduced quickly when all the other things are taken into consideration such as AC, ventilation/filtration, nug quality, bulb replacement costs, and direct electrical costs.
The COB advantage will continue to grow. Jair from Gavita pointed out that HPS has made small efficiency gains in recent years and he expects more small efficiency gains in the coming years. Meanwhile, commercial COB lamps are suddenly topping 40% efficiency and
DIYers are building 63.8% efficient flower lamps, 70% efficient vegging lamps. That represents a ground breaking reduction in heat and gradually commercial COB fixtures will push that direction and or get cheaper.
Jair from Gavita, guest on Adam Dunn
