New to Indoors-Lighting Question

First, understand a plant can only handle so much light per 24 hours -- relative to atmospheric CO2 and even temp/RH too. Better environment / more co2 = more light per day possible. it is proportional to hours of use. So, when going from 18hour vege to 12 hour bloom, you need 150% of the light you had before with 2/3rds the hours of operaiotn (2/3 * 150% = 1) Fore the most part, wehther you provide that "max" over 12 hours or 18 it doesn't matter much. though obviously with photoperiods, we have no choice on teh 12/12 schedule (actualyl more accurate to say >10hours of uninterrupted darkness per day) So, you want to work backward from what tht light is capable of growing well on a 12/12 cycle, or you may not be able to provide enough energy when you get there to full develop a "too large" plant for that light. 300w but middling efficacy at best, so maybe 35-40w/ sq ft is a good starting point. 300 / 40 = 7.5sq ft... let's just say it's good for a 3x3 space and some equipment, like a fan, eating up some sq footage. You'd want to choose a distance from canopy that best covers that area... a free lux meter app on your phone is enough to help witt this. Try to make the difference between center and outer areas as similar as possible -- do expect some drop off from center to corners, of course... your central area will still be your wheelhouse and you don't want to sacrifice too much for the edges, but it shouldn't be too drastic at 18-24" from canopy... This is likely your best range of height with a QB (quantum board type frame / light structure). So, 18-24" covering a 3x3 over 18hours is a bit too much at 100%... dim to 66-70% and go from there.... These are good suggestions to start out, but you will need to refine them further through observation. If the plant can handle more, give it. Use resulting distance between growth nodes to guide your choices. Too tight is bad. Too stretched out is bad. find that happy zone between where you get good number of nodes but also sturdier branches and trunk. if you find it can handle a lot more than 66%, there's a good chance your light will be a bit lacking in 12/12 bloom cycle if you can't give 150% --- this does not equate to "doom". A little lessis no problem.. a lot less might be. Read up on DLI (daily light integral) -- you don't need to know the math, you just need to usderstandt he concept of providing light and an apples to apples way of measuring it... e.g. i could just tell you that you need a minimum of 22 DLI to produce decent buds -- this is true for any sized garden and any hours of use per day of light. Much easier when ppl understand this metric when attempting to commnicate these concepts. ambient co2 ceiling is 35-40DLI... anything above that will eventually burn the plant. There is variance due to genetics, temperatures, and ambient co2 is not always the same either. So, these are ballpark concepts where you start in a good spot with minimal adjustments likely needed as you obseve and react to the plant. Take notes... it'll be similar next time... and relative to your garden, you will start at an even better spot "next" time using past experiences in your garden. You may not need a further adjustment, but cannot assume that - espeically if you live in a region with different seasons or whatever else changes day to day / month to month. With all of that said.. same concepts at work.. with autoflowers, you can cover a larger area with that light over 18hours per day... or more if you choose to, but a dark period is still beneficial. less light per hours, but more hours per day can cover a larger space. I speak of "max DLI" or max per day, but that doesn't mean you HAVE TO max out.. however, less than 22DLI will result in larfy buds... less light or too little light = greater proportion of larf and poorly formed buds. we would need some massive sample size experiments to determing what is "optimal" for yield or any other concern. so, i'm not saying this maximizes yield per watt, but i would say it maximizes quality by providing as much DLI as it can handle. it will improve yield too, but is it better yield per watt slightly below max? i wouldn't assume such a thing, but defintiely better than lower levels of minimal light though, like 22-ish DLI.