I run 3 Autocobs in my 2x4 and I can confirm what @slowandeasy says about it being perfect. I’ve never felt as though there was ever a lack of light nor did I ever consider trying to add another.What are you feeding them? What medium? 3 Autocobs in the 2x4 is actually perfect. Please don't take this the wrong way, but if you grew Ripley's in a 2x4...you did something wrong. No way 3 should fit til harvest in 3 Gal pots. 3 properly grown Sour Crack will fit. But only 1 Ripley's would fit in that area if you do things right.