Consider the SUN is 14,714 W/SQ/Ft
I use a 1000w hortilux at 24-28 inches for seedlings and a 4 x 4 area. And have for decades. Around 62w Sq/ft
The 600w/1000w/400w ect Hortilux HPS Superbulb are plant bulbs. Its basically a High Pressure Sodium, which are rich in reds ect, and they add Blue so the spectrum becomes plant friendly. Ive been using these bulbs for over 20 years. Don't over think it. The main thing to take into consideration is the HPS will generate more heat, because its putting out a lot of energy.
1 of the biggest reason HID burn plants is because of Infra Red, not because its to bright.
Ive not been able to get a 1000w Gavita any closer then 36 inches without burning them, 38 minimum, just as they recommend, as where I can get a 1000w Hortilux 15 inches away if ambient temps allow, and no bleaching. The infrared on the Gavita is easily noticeable vs the same watts. Gavita also puts out almost 25% more photons at 38 inches, and 21,000 more lumens vs Hortilux at around 2 feet distance
T5s ect have a really good spectrum ect, but wont generate anywhere near the light energy for the $$, and the plants will thus grow slower, and use less water. IMHO its all about using water, food, and getting the plants photosynthesizing/metabolizing as hard as it can go. I also believe that less plants vegged with heavy duty light/photon output, a lot of soil to get big roots, will out perform more plants, vegged with less light intensity.
If you can find it, Id also look into Promix BX for your base. It has no nutrients other than a bit of Lime which will give a bit of Calcium/Magnesium, but not enough. But I would use a good peat based mix, with Vermiculite/Perlite/ Calcitic/Dolomitic Lime added. Or make up my own.
Promix is a good light mix that will give good aeration, so the roots can grow fast, thus using more food, and water, giving you bigger plants, faster growing plants for the time vegged.
IMHO you can veg the crap out on 5 plants in a 4 x 4 and 5 gallon containers and 600w Hortilux HPS.
My buddy vegges his inside here in USA/ MID OHIO under 2 x 1000w HPS 5 gallon containers, and then puts them out the last week of June, and uses the natural light like youre explaining, and has really good success with it.
He digs out his own holes outside for transplanting, and uses 1 Bale 3.8 cu/ft Promix per plant/hole.
But if you don't need 4 x 4, and 600w, I just go by w/sq/ft.... YMMV, .Mine wont as Ive been doing this for 40 years this way. I used to use Metal Halide, before they had the color corrected plant bulbs like now.
But I like all the light I can get, up to a point. Of course you can have to much, but 60w sq/ft aint it.
You also may look into the Ceramic Metal Halide 315w, but they may be hard to find.
Also don't forget about penetration. As a plant get bigger, the lights get further away from the lower secondaries, can case stretch, and weak branches. Light intensity quickly diminishes from just inches. Inverse Square Law.
Light and other electromagnetic radiation[edit]
The
intensity (or
illuminance or
irradiance) of
light or other linear waves radiating from a
point source (energy per unit of area perpendicular to the source) is inversely proportional to the square of the distance from the source; so an object (of the same size) twice as far away, receives only one-quarter the
energy (in the same time period).
More generally, the irradiance,
i.e., the intensity (or
power per unit area in the direction of
propagation), of a
spherical wavefront varies inversely with the square of the distance from the source (assuming there are no losses caused by
absorption or
scattering).
For example, the intensity of radiation from the
Sun is 9126
watts per square meter at the distance of
Mercury (0.387
AU); but only 1367 watts per square meter at the distance of
Earth (1 AU)—an approximate threefold increase in distance results in an approximate ninefold decrease in intensity of radiation.
