I agree in a FPI or sphere test the COB with no optic would have most light. Reflectors and lens have their losses.
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But in a grow room things are slightly more complex. Cobs have light coming even almost at 90 degrees to sides. All that light on sides would be lost if walls are not reflective. In bigger grow rooms you may not have side walls and actually open space to walk and again all that side light is wasted. Optics can help redirect this side light towards plants.
Even if sides are reflective, in a recent experiment i found the amount of light exiting from top of grow tent reduced when i put a reflector or lens.
I think this was because a lot of light emitted wide angles when hits the reflective sides get reflected up. A lens or reflector can tighten the beam enough so that more light reaches plants.
The slightly stronger light with optics may penetrate better. but then you an argue the diffused light reflected from sides increase penetration more. more Even coverage, LES protection, IP are other advantages of optics as well. but optics have $5-$11/COB price or even more .
I like the idea of using a suitable reflectors and lens, some may not.
I would love to know if anyone used 90 degree Angelina reflector or KB 80/120 lens and does not plan on using them anymore for next grow.
I did not say ledil stella or smaller 77mm 90 degree lens and other optics that may make the beam too tight.