Gego, it's not my analysis, it's basic science.
Black pigments reflect no visible wavelengths (which is why it looks black), and white pigments reflect all wavelengths. If the light is not reflected, it is absorbed. Energy does not just disappear: if that light energy is absorbed, it is turned into heat.
Put a piece of white paper and one of black paper out in the sun, after a few minutes, if you put your hand over each, you'll note a significant temperature difference, and the white one won't be hotter.
Hey Ray, like what I said we are on the same page, black doesn't reflect, so light is absorbed, energy turned to heat and dissipated on the cloth. That's what I said.
I don't what to go deep into it so I just said "heat is absorbed".
I would rather block the light than reflect it if the reflection is a) only partial and b) the direction of the reflection is not totally away from the gh.
My point is if I'm not very clear yet, is that if I have 50% shade, I prefer that I block 100% of that 50% blocked light (if possible) not reflected but blocked. And that black cloth will do a better job.
Then under the black shade add another layer than can insulate and keep that heat absorbed by the cloth from flowing down to your greenhouse. And we know hot air rises. Place some good distance between them so airflow can blow the heat out. This is the trap.
A plastic sheeting is good for the next layer so the 50% light that went thru will be diffused and spread nicely/evenly to the gh. If you still need more shading after this, then add a white cloth below the plastic sheeting.
50% of light is still a lot of light. If the sun is providing 10,000 FC, you will have at least 5000FC (ave) for your plants. If you place a vanda close to the shade you may have a yellow leafed vanda in a short time.
You better read my post again, lol, if there is a shade that will 100% reflect that light away back to the sky then that is my ideal shade.
Better check with your neighbors though,,,,
