There are some bubble systems which blow soap-like bubbles between the layers of glazing. These can have different characteristics including light exclusion. I know it sounds a bit crazy, but apparently it works. Note, though, that as far as I understand there is some dispute about who invented this (and owns the patent for it). Also I talked to one company about this for our greenhouse, but they were not very interested in quoting for us since we are out in the middle-of-nowhere and our greenhouse is measured in partial hectares not tens of hectares. I don’t know of anyone who works with small greenhouses on this technology.