At one of the online sellers where I have bought a good number of orchids, they provide recommended light levels. However, when they use the description 'strong' light, their highest classification, they match it with the number '2,000+ f.c.' So I know this is not very high, so I presume it is a minimum.
So to take an example, one Orchid classified as liking strong light, 2,000+ f.c., on that website is the Oncidium Jiaho Queen. So is 40% shade cloth suitable for this plant?