Hank,
Good question! I have a 20 Watt UV light like this:
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It has the light powered turntable to rotate the parts during exposure. I mounted it in a hole in the side of a cardboard box and lined the box with crumpled aluminum foil to get good light scattering.
Some sites say to expose for very short periods - a minute or less - for small parts and up to 5 minutes for "large" parts. However, like a lot of what you see on the Internet, they never say what light intensity they use. And I have never seen any data on the proper exposure times for resins on manufacturer's web sites.
I have been guessing at exposure time to cure the printed parts. I read that overexposed parts have crusty white areas, and I have seen this happen on some Anycubic Basic Grey parts that were exposed for more than 10 minutes. For very thin and small parts I have been exposing for a total exposure time of a minute or two. Larger (1" to 2") parts have been exposed up to 6-9 minutes total exposure times without getting the white "burn."
I typically expose parts in two to three separate short intervals, rotating the parts between burns to get a more even exposure. So a 9 minute exposure is done with three separate 3 minute exposures.
I am guessing because the manufacturer's don't give a clue as to shat light intensity (lumens) and exposure times are needed to properly cure the parts. The Anycubic Basic Grey cures to a firm surface in just a few minutes, but the Pfrozen Fast Black seems to be a bit sticky with the same cure times.
Tom has mentioned that he allows the Fast Black parts "dry" for a while (unspecified time) after printing, and I think he means before curing. This may be a consideration for water washable resins.
Like I said, I am just guessing.
Phil