Chrysanthemum blackout curtains?
A friend of mine got a job in a greenhouse and I got a chance to visit during the end of the construction before they start operating.
During the tour, I asked if he could shut the blackout screens so that I could see how dark it got in there. With the curtains drawn, it was quite dark, but not pitch black. It was dark enough that I couldn't see obstacles on the floor, but there were little pin holes visible through the curtains, and a couple spots along the edges that leaked very sightly. It was mid afternoon on a very sunny day.
When I voiced my concerns that I thought it needed to be darker he said the dutch manufacturer had insisted that it was "dark enough" and said this is what they use for chrysanthemums in Holland.
I've done much googling and cannot seem to find any info on the relative difference in darkness levels required by cannabis vs chrysanthemums, but I suspect my friend is in trouble here. i'm an indoor guy and have always achieved total darkness so I have no experience growing with minor light leaks.
Any insight into this would be very helpful.