DLI

oops "it is the same number of photons over 12 or 18 hours IF it is the same DLI .... i left that ending out below. same number of photons = same energy applied = roughyl same photosynthesis occuring... is 6 hours difference enough to make a difference? studies say no, but could be small impact.

DLI is relative to hours of use.. it's included in teh value already... photons (of PAR wavelengths) per second multiplied by hours of use per meter squared is what dli is, roughly... it is teh same number of photons over 12 or 18 hours per incremental area... 35-40DLI is a good rough guesstimate of ceiling for ambient CO2 -- carbon dioxide is the limiting factor. Avoiding temp and rh extreme is probably enough for this, though you will get benefits from tight control too. 50-60DLI can be used with boosted co2 and a tightly controlled environment to maximize that co2. if paying for co2, might as well keep your VPD in more precise control (vpd is result of temp/rh around the leaves and it is primar driver of plant's water intake per day) Simply use a table. or this calculator i found in a matter of second -- https://www.waveformlighting.com/horticulture/daily-light-integral-dli-calculator 600 ppfd over 18 hours is 39DLI do you have a umol/s specification for your light? divide that by your area in meters-squared. that is your ppfd. type that ppfd into the link above and 18 hours... hit calculate.. that's your DLI. some manufacturers lie their fucking asses off on spec sheets... hopefully you got on ethat is okay. The old rule of thumb for hps was 50w/sq ft.... and if all hps are equivalent in efficacy, this would apply very well to most situations. Efficacy matters... if yo ahve that specification you can multiple it by total watts of light to determine umol/s e.g. if it says 1.9 umol/J efficacy... and 1000w... That is 1900umol/s .. you can cover a nearly 3m^2 area with that and hit max DLI. (1900 / 600 = 3.17m^2 -- this is taking teh 600 ppfd (ppfd = umol/s per m^2) above because we know that is ~39DLI. you could also work backward from a dli table with a different target.. .but the ballpark idea is good enough... still need to observe and react to plants for signs of too much / too little light. So your light produced photons per second (umol/s) and how much that spreads out (area) and how long you use it (hours per day) are what make up DLI. DLI is apples to apples... if i apply 39dli, it's the same measurement as you applying 39dli regardless of hours of use or size of garden. it is proporitonal. Now, it does not mean the "max" is teh same in every garden... local variables will cause different values to by "your" max in "your" garden. YMMV as to what that max is. it's still a good guide and starting point for smaller / faster adjustments to get to optimal.

Yeah my plants are suffering, I've tried pretty much everything else but this ... Im running 600W hps and they are about 10inch away

You can easily do this with a DLI cal.. It'll ask you things you didn't add. How many plants. Size, and other factors. And also. DLI is very advanced. I'd focus on the 101s. Lights, nutes, co2 = photosynthesis. LST will be a major role growing indoors. As will defoliation be much more relevant to your needs. Good Growing