I have a mercury vapor light mounted on my carport and right under that light is an arbor with honeysuckle growing on it. the first year I had installed the arbor and planted the vine I was at a loss why this crazy thing kept growing all winter but just in one spot then it dawned on my that even though the temperatures would get to freezing and below this thing was getting ultraviolet rays from the mercury vapor light. I know its a little off the subject but I felt so dumb when I finally figured it out.