CactiGuide.com

I just installed a 30% sun shading for my southern exposure lean to greenhouse roof. Live near Baltimore me do you think it is too much shading for cactus without it using just the clear poltroon the plants were cooking

I use 30% but I'm in Australia so not sure how strong your sun is.

You can get away with intense sun if you have more ventilation by opening doors and windows

You can measure light flux.

Full sun is 2000 lumens.
I use a shade cloth and the light flux in greenhouse is 1000~1500 lumens.
Cacti can grow in 500~2000 lumens but I set a soft light flux level because many young cacti are in my greenhouse.