Fluorescent tubes and UV

Gregor Trinkaus-Randall <gtrinkaus-randall<-a t->state< . >ma< . >us> writes

>Most of these institutions are lit with fluorescent tubes.  Most
>also do not have UV-filtering sleeves on these tubes.  However, many
>of them, the tubes that is, are located above the plastic shields
>that cover the bottom of the "boxes" in which the tubes are housed.
>Even so, I expected to get high UV readings below these lights. Much
>to my surprise, the readings are low - around 10uM/lumen or 2-3
>uM/M2.

Murray Frost in his article "Planning for preventive conservation",
in The Manual of Museum Planning (1991), p 127-160, states

   "If the fluorescent fixtures are of the 'commercial' style, where
    the fluorescent lamps are fully enclosed by metal and solid
    acrylic diffusing panels, then there is also no need to worry
    about UV levels.  Every commercial-style fixture on which I have
    taken UV readings, in many different institutions over many
    years, has always tested less than 75 uwatts per lumen according
    to a Crawford 760 UV meter, no matter which fluorescent lamp has
    been fitted.

   "It is not necessary to buy the special, expensive solid acrylic
    diffusing panels that are marked as being UV-reducing, since all
    acrylic diffusing panels have an ultraviolet absorber cast in to
    prevent yellowing and brittleness."

I can confirm these findings of Murray Frost, which demonstrates the
need to measure the illumination and UV outputs of all lighting
systems in the museum/gallery/archive before taking preventive
measures.  How long the diffusers will last will depend on the UV
output of the fluorescent lamps and how long there are switched on.
It is recommended that they are checked at least once every 5 years.

                                  ***
                  Conservation DistList Instance 10:62
                 Distributed: Friday, January 10, 1997
                       Message Id: cdl-10-62-002
                                  ***