Start at 24" with that type of light. As long as the light isn't too strong, pick height to fit light footprint to canopy. While a lux meter doesn't tell you how much photosynthetic light is emitted, it is proportional. you can use it to make position and choose a height based on readings in corners and edges etc... much cheaper item than a par metere. or ppfd meter? umol/s? haha you get the idea.
Signs in bloom it is too close: trichomes develop below top of canopy, but not as thick on top (evaporating due to heat or too much light); Any leaves turning pale - starts interveinal and quickly spreads. happens at top, obviously.
in vege, too much light will cause new nodes to stack nearly on top of each other. The leaves will get pale too.
hours of use depends on strength of light. I am not familiar with this light. Even 16/8 can be effective for many contexts. I'd suggest 18/6, unless you think it's a very weak light.
in the time i have to grow a plant, 16/8 works well for me, so i save 1/9th the cost for that portion. Bloom cycle is when you care about maximizing all you can. Vege is great if it grows with acceptable internodal distances and grows fast enough for your needs.
If you see the plant always drooping the last 2 hours of lights being on, it's likely had it's fill for the day and it's not doing a lot with the photons pelting it at that point. There's something called DLI. There's a limit as to how much light your plant can use in 24 hours, and it can more easily be reached while running lights longer than the 12 hours in bloom - which is the main reason your bloom lights need to be ~50% stronger because they have 33% less time (18->12).
Giving it more than it can take will only hurt your plant. light and dark processes occur all the time in the plant, but giving it some dark is still beneficial. There's an optimum amount of light you want to provde to your plants.
Watts can help you compare prodcuts sold by the same company, but doesn't correlate to much otherwise. Without knowing efficiency of the light, you have no idea how many of those watts are merely generating heat instead of light. Plus that 1000w value is an 'equivalent-to' value, not likely the actual draw from the wall, and not equivalent to 1000w anyway.
That doesn't mean it's bad. I have a light that says it's 1800w but is only 270-280w. It is a common practice with many brands. fwiw, i'm replacing that 270 with a light that runs at 240W and probably provides 25%-33% more light than the 270w fixture and with fewer watts. It lasts 3x longer but costs 3x more, and provides more light over that time at a lower incremental cost.
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