A random question about increasing watts; if you double wattage (600w -> 1200w) would you expect a double in yield, given all other factors are equal?
No. Yield can increase faster than wattage. Consider a 400w that is illuminating a 2.5'x2.5' area with four 5gal buckets in a 2x2 square. Upgrading to a 600w would support roughly a 50% wider area, or 3.75' wide. Because the stronger light is emitted in all directions, you'd then have a 3.75'x3.75' area that supports 3x3 5gal buckets, or nine plants. Every 200w gets you another row of 5gal buckets in both directions. 4x4 (16) with an 800w, 5x5 (25) with a 1000w. # of Plants: Wattage/#====Watts per plant 4: 400/4================100 9: 600/9================66 2/3 16: 800/16==============50 25: 1000/25=============40 36: 1200/36=============33 1/3
As simple as it may sound, "all other factors being equal" is a knotty concept. Do you mean double the wattage on the same number of plants, or doubling the number of plants as well? Same area, or doubling the area? Doubling the wattage by adding a second of the same wattage light, or by switching out to a single light that is double the wattage? All of these are important considerations that will impact harvest.
"All other factors being equal" as in; Same grow space/setup (indoor tent w/ ventilation, etc.) Same number of plants (say 6) Same strain Same time frame Same nutes/soil/etc. Same time of the year The ONLY change is that you go from one (1) 600w light to two (2) 600w lights.
Adding a second light of the same wattage with the same airflow systems and growing the plants the same way, you should definitely get around twice the yield. Replacing the current lamp with one that's twice the wattage should be able to nearly triple your yield, provided that you're able to keep the same temps.