Adult trout lack the visual cones capable of seeing UV light, so the use of UV paint or thread on lures and flies will not make trout more likely to strike. Trout will see them just like any other lure or fly, so if it’s a suitable color or pattern for the prevailing conditions they will be as effective as any other lure. UV trout flies and lures designs are to catch fishermen not fish.
It is true that young trout, under two years of age do have the ability to see in the ultraviolet. Trout lose that ability sometime before reaching their second year of life. So, if you are targeting fast growing stock trout less than two years of age, they should be able to see ultraviolet. Stock trout can be 15 inches before their first birthday which is a respetable size.
I remember back in the early 2000’s I was working with a indepdent lure manufactuering who was keen to add UV to his range. It was all the hype at the time, and they certainly sold well. But in all of our trails, it really did not outproduce a comparable lure that lacks a ultraviolet compouind.
Many fishermen beleive that ultraviolet gives an advantage when water clarity is reduced, other fishermen claim it works well on overcast cloudy days.I personally find that the bright fluroscent colors which typically accompany lures that feature ultraviolet is likely what the trout are picking up.
In my view, ultraviolet is not worth the extra expense. It is just one additional color, it is not goign to be any more effective than changing froma yellow hot spot to a pink hot spot. So I certainly advise against paying a premium for it. It is not going to hurt your chances, so play around with such lures if you so desire, but do not expect miracles.