FWIW, I have two 4 foot x 6 foot 6 inch tall frag tanks that was having cyano problems in plague proportions. I tried everything under the sun to remove nutrients and nothing worked so i put a emperor aquatics UV unit on and while it didn't solve the problem entirely cut cut the cyano down by 75% at least. eventually i found the problem to be my GE 65k t5 bulbs.
Just as a bit of background on these tanks, they only had one fish each and I rarely fed them. i did huge water changes,short photo periods, phosphate removers and all tests always said zero. however i had so much cyano that after a few days there would be so many air bubbles in it that the eggcrate (with frags) would float to the surface ... I don't think the water could have been any cleaner at the time . at one point i changed a few of the bulbs out from the GE 65k's to some blue+'s and the cyano went away in days on that side of the tank. I then switched them around and had the same results and the cyano came back with full force under the 65k . so i then moved the blue+ to the other frag tank that shares the same water and had the same results. I know the 65k's have more par than blue+ but i don't think it is that significant that it would have this kinda night and day effect with cyano. Everyone has their own theories on cyno but i no longer believe that water nutrients are the main driving force for cyano and bulbs certainly have effect , however i cant diffinately say its the PAR or color that really mattered , maybe both. Please be aware that much of this is anecdotal and not really any proof of anything but it was enough for me to form an opinion : )
my UV now sits in the corner unused because i can not justify the power and cost of bulb changes when it is not being used to treat anything specific.
so while i have used both at one time i choose "I don't run anything." in your poll