Led dimmer

Those lights are roughly 140w. Shouldn't need a dimmer. Your plant is plenty old enough to handle the intensity of that fixture. The only problem I see is the headspace in your box.
I have two bloomspect LEDs, and the hangers for them are 14 inches. When you switch to 12/12 light, that plant is going to stretch to about double it's height and take up alot of the vertical space you have.
Also.. For your 2x2 space, you'll need another light to get any decent results.

 

I don't think it will be a problem for anything past seedlings. So long as you can keep like 14-18 inches between the light and canopy. I could be wrong, so I'd consider other opinions on the subject from more experienced growers. I'm still pretty new to it. But that's my understanding on color mixing and light intensity of these type of led fixtures. I keep mine about 16" and the plant seems happy with it.

 

That's understandable. There's problems tho. Those lights, I believe, have 60° reflectors. With that narrow of an angle, the intensity in close proximity will be really focused. What you end up with is patchy spectrum distribution and light burn (not heat). Led is alot different than the classic mh and hps. A 150w hps at 6 inches or so is alot less focused, intense lighting compared to 150w led at 6 inches.

I'm no expert and could be way off, but that's my understanding of the subject.

It may benifit your setup to run a grid and use scrog on it to keep your canopy as low and even as possible and give yourself more head space in the box.

 

I've been reading tru alot of posts on here about it. I used LST on my current grow. I'll have a proper tent set up for my next grow, and I'm going to do scrog for the first time.
Basically, run some twine or similar across your grow space like chicken wire a few inches above your topped plant. As the growth comes above the netting, tuck it back under. Keep going like that until you switch to flower. At that point, there are varying methods. Some say let it go from there while others have said keep tucking for a week or two after. Then you basically strip everything under the screen and let them grow till harvest. Seems to be the perfect way to grow in small spaces and to get better yields.