Fluorescent tubes and UV

In Instance 10:68, Michael T. Stieber <mstieber<-a t->mortonarb< . >org> asks
whether cool white or warm white tubes are the best substitute for
"natural" fluorescent tubes. Neither is particularly good, but the
cool white is probably better than the warm white, which give a very
pink colour cast.  There is nothing to choose between them from the
point of view of heat output.  UV-absorbing sleeves will last maybe
five years, maybe more--it is important to check regularly using a
UV meter.

** The following message was received from Michael Stieber:

    To: "B.Knight" <barry<-a t->eng-h< . >gov< . >uk>
    Date: 30 Jan 97
    Subject: Re: Fluorescent tubes

    Thank you for your prompt response to a problem that vexes our
    supplies department.  Bulbs are not cheap, and they were worried
    about using the "proper" type with the UV-absorbing sleeves.  I
    presume that the near 5-year lifespan applies to the
    UV-protected bulbs, as well, or is their lifespan longer?  I
    would appreciate an answer on that one, if you know.  (We have
    our reference room in the library equipped with those bulbs.)
    The sleeves are going into our display cases.  Michael
    Stieber/Administrative & Reference Librarian

    Michael Stieber
    Sterling Morton Library
    mstieber<-a t->mortonarb< . >org

Michael,

I'm sorry if I didn't make myself clear.  The UV-absorbing sleeves
should last about five years, but it is sensible to check them
regularly.  The lifetime of the fluorescent tubes themselves depends
on a number of factors such as frequency of switching.  The light
output falls gradually over time so you would probably want to
change them before they actually fail completely.  The General
Electric data I have gives an average lifetime of 9000 hours for
most types of tube, there being no difference between the different
kinds of phosphor (colour type).  I hope this makes sense,

Barry Knight
English Heritage
London

Barry Knight
English Heritage
London

                                  ***
                  Conservation DistList Instance 10:69
                 Distributed: Monday, February 3, 1997
                       Message Id: cdl-10-69-002
                                  ***