I did some online research which suggested that utraviolet light might have a small effect on stunting growth of some plants (it seemed mostly to effect annuals):
Source 1
Both plants and phytoplankton vary widely in their sensitivity to UV-B. When over 200 agricultural plants were tested, more than half showed sensitivity to UV-B light. Other plants showed neglible effects or even a small increase in vigor. Even within a species there were marked differences; for example one variety of soybean showed a 16% decrease in growth while another variety of the same soybean showed no effect [R.Parson]. An increase in UV-B could cause a shift in population rather than a large die-off of plants .
(http://www.nas.nasa.gov/About/Education/Ozone/radiation.html)
Source 2
Dr. Brent Pemberton has found that exposing plants such as impatiens, tomatoes and cucumbers to ultraviolet B, (UV-B) treatments for a few hours slows their foliar growth and stem length without reducing color or other favorable characteristics.
"Simply put, it acts as a growth regulator and stunts them somewhat, but with bedding plants this may be desirable," said Pemberton, who is based at the Texas A&M University Research and Extension Center at Overton.
(Writer: Robert Burns (903) 834-6191,d-burns@tamu.edu Source: Dr. Brent Pemberton (903) 834-6191,b-pemberton@tamu.edu)
Source 3
Conclusions/Discussion The pea pods from the UV Blocked environment were also the heaviest and had the highest number of peas per pod. A surprising result was that some of the pots in the Control Group environment produced no peas. Also, a mold developed on the plants in the UV Light Blocked environment. This is probably because ultraviolet light is necessary for the production of vitamins which inhibits the mold growth. The plants in the UV Light Blocked environment were likely unable to produce the vitamins to stop the growth of the mold.
http://74.6.117.48/search/srpcache?...a&icp=1&.intl=us&sig=JqxIUowpqLuYGuwXXeFRKg--
My apologies to Mr. Adams. It appears that ultraviolet light does impact growth .... somewhat.