150w hps should do you fine. The pic above was 72w of good LED light (not a crappy UFO)
150w hps should do 40cm2 (or at a push 50cm2) for a scrog.
May I suggest you supplement your hps with about 4-8 good Cree 455nm royal blue LEDs. If you have a look at the spectral output of a hps it is really weak in the blue department but strong for the red end of the spectrum. About 5% of the light energy should be in the blue spectrum for optimum growth. The blue LEDs for reef tanks are ideal for this and led group buy is brilliant for components.
You should be able to get 150 to 165 g with your light plus a few blue LEDs.
It does not get properly mentioned that photosynthesis is like a triangle with heat, light and co2. If any of these factors are deficient increasing the others will be of no use. These factors need the correct balance and to much of either will bring your grow away from optimum. To many people focus on all these boost additives you can buy without taking into account that photosynthesis provides the energy to use these additives. So unless you have your triangle of light, heat and co2 spot on then the additives are just an expensive gimmick.
When trying to improve your setup focus on the weak point be it light, temp or ventilation(co2).
If doing a bedroom grow always grow at night when you will be asleep or in your room. You will raise the co2 level for your plant just by being there.
For a SCROG I always let the plant grow two sets of internodes then cut the top off above this point. After this I give it three more days of 18 / 6 then reduce the light by one hour a day until I hit 12 / 12.
I also cut some holes in the top of my pot and as the plant grows its four branches (from the two sets of internodes) I train these to grow outwards to the side of the pot using thin wire.
When the plant has filled the diameter of the pot then I would put the screen above and train the plant under the screen for a further two weeks(ish) and then let it grow up and flower.
You can control the growth buy lowering the tips and redistributing auxins (google them) to the lower branches/ bud sites.
Now for a controversial tip. If I have any buds growing to high and making the canopy uneven I cut the tops off before they grow any more than half a gram of flower.
I have put up a picture of a plant one week into 12 / 12 under 72w led and another of a fluffy bud. All my pics are quite old as my gf deleted all my newer ones.
Back in the day I used to use 1000w with DWC for bigger grows but now I use 115w of led and coir and aim for 130 to 140g nice herb (just for me) from a small grow. I would like to get it up to 150 to 160 but that will be breaking 1000g per m2 which is hard to do (especially with high grade genetics).
You will find a lot of people on grow forums arguing about what lights or grow medium are best but what it really boils down to is maximising the potential in your grow space providing the triangle for photosynthesis and finding what techniques work best for that area. What works well on a large scale may not on a small scale and vice versa.
Anyway all the best with your next grow.
Peace
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