i have a HPS 400w right now and i want to flower 2 of my plants.. i hear you can flower both on a single 400w HPS light. But would i yield more if i had 1 for each plant?
Another 400w HPS can increase your yield significantly on one plant let alone 2. That being said , you gotta controll more variables such as heat , humidity and ventilation for sure , otherwise it would be pointless. If you can controll them and have a 2 x 400 watt HPS over 2 plants , you will definately notice a difference. Strain also plays a factor , but even low producers yields can be increased.
I think you would get a better yield with 4 plants under a 400w than one under a 400w. Just in sheer number I think you would get considerably more. 1 under a 400 seems a bit overkill to me.
For 2 plants I would just use the one 400W and supplement it in areas it may miss with either LED's or CFL's.
Sure, in my opinion you can grow more on 4 plants, than one. I don't know how I can simplify it anymore. Think of things this way, let's say you have a big garden outside, enough for at least 4 tomato plants, but instead you just plant one so it can soak up all the sun by itself. I think you would get more tomatoes from 4 plants. I mean I don't have any charts or graphs to prove this, but it seems logical to me. Utilize your space for maximum yield. With a 400w hps, I wouldn't do any more or less than 4 plants (100w each, which is about perfect). There is plenty of light for them. Look, if you want to just grow one plant under your light, then please, by all means. But I personally couldn't think of how one plant will produce more than four, unless you had limited lighting, but in your case, you have ample lighting even without any kind of supplemental lighting .
you might as well use 400 watts for two plants. i agree w/ 400watts on one plant being overkill (unless its a 4 month vegged out clone or something) its in your best interest to utilize the space you have more effectively. i am also thinking you can probably cut more clones off of two plants that one plant.
it really depends on veg time, plants being used, etc.... the best way to figure it out is working backwards IMO. See how much space you have, and how hot it would be with 1 and with 2 400w lights. If space allows the use of 2 lights, then continue. Now that you have a given space, you need to figure out how to maximize your canopy....since the canopy gets the primo light. If you have a limited veg period, then its probably easier to achieve a full canopy with the larger number of plants....this is the SOG methodology. If however you can train your plants successfully into growing more evenly / canopy friendly, then you can go with less plants....maybe even 1 per light. But, keep in mind, you wont be maximizing yield until you max out your canopy...cause this is where a majority of your yield will occur. So, this would be more in line with how people grow using ScrOG or LST. you take a plant, let it grow a single cola / christmas tree shape, and throw it under a 400w hps light by itself, you can see all the canopy light youre wasting. Do what you have to do to use this light.
Keep it at the one. It you are using 800 watts I would suggest at least 5 plants to make it worth it. -C