FYI, in my applied sciences/greenhouse management classes, we learned that greenhouses do not magnify light. They diffuse it.
It's that diffusion of light that is beneficial to plants. Plants do not necessarily need "maximum" light (a common misconception) - they need evenly spread light. Diffusion is scattered light waves - small intense beams of light break apart and are spread more evenly throughout a greenhouse. (of course this is also dependant on other factors, like whether the glass has been treated, or whitewashed).
Think of it like driving in a thick fog with your high beams on. Your headlights make a wall of light in front of your car making it almost impossible to see, or tell where the light is coming from. Same thing happens, to a degree, in the greenhouse.
Direct light is worse for plants, because it is more intense, and creates both shadows and intensely burning rays. The diffused light is not directional - it scatters and spreads uniformly, seeming to come from many directions, which is the best kind of lighting for plants (and photography, btw). Plants photosynthesize using the light at the edges of the visible spectrum on both sides (e.g. the red and blue parts of the spectrum). Diffused light is more beneficial to photosynthesis because the light "bends" around the corners and reaches the lower leaves more than direct light which creates shadows on the plants when it hits the upper canopy.
Additionally, when light is diffused, it helps to prevent hot spots in a greenhouse, improving the consistency of your climate control, and thus providing optimal temperature ranges - or at least evenly disbursed temperatures so that all of your plants grow consistently, further benefitting production.
Your best lighting is full spectrum evenly spread light. This is exactly the effect that a greenhouse has on lighting (again, depending on treatment of the glass or polymer), and why plants respond so well to it.
If memory serves, a milky white coating will provide the best diffusion - to the naked eye the lighting will appear dimmer, but to the plants, this is the best way to provide the usable spectrum for photosynthesis.
Hope this helps.
