I often read that when choosing lighting for a grow room one should aim for a minimum of 50w per square foot. I was curious what the impact is if more or less light is used. If, for example, 40w per square foot is used will the plants grow too slow making it a waste of electricity, or will it simply not reach all parts of the plant. What if it is 30-40w per square foot, but the entire tent is not used, how will this impact the plant. Conversely, if I have 80w per sqaure foot (assuming heat is not an issue) will the plant grow that much/better faster? Any information would be appreciated. Thanks
More light = more bud. Say you have a 4 x 4 area. So, trying to use a 400w lamp over that area is only going to equal 25w per sq ft. That same area with 1000w is going to be 62.5w per sq ft. Given all other factors are equal, the higher watts per square foot will mean higher yield. There is a point of overkill, but you get the idea. Higher intensity lamps also have more penetration in to the canopy. A 400w will only penetrate well about 1.5 feet where as a 1000w will do 2.5 if I remember correctly. Better penetration means you can utilize more of your vertical space. More space utilized for bud production means more yield. Basically once you go outside of your lights primary area bud density and production will drop off. It goes by the area you actually use for plants as well. That 400w lamp would be 44.4 w per sq ft if you only used a 3 x 3 area. Its primary lighting area of 2 x 2 would have 100w per sq ft. The majority of us end up filling whatever tent we buy, so I would recommend buying a light that covers your entire tent.
Watts per square foot mean little to plants, they mean a lot to warehouse lighting, but not plants. Daily Light Integral is what means something to plants and it would serve all well to learn how to measure and apply that.