Lighting for butterfly collection

Because this relates to a posting about use of flash photography in
exhibits, i.e., effects of light, I am forwarding this to the
Conservation DistList.

I would like to seek further advice with respect to the effective
display of the Barcant Butterfly Collection by its owner, the
Angostura Company. The one serious technical problem that remains is
lighting.  I am concerned that the panels on display should be well
enough lit that visiting members of the public can get a good look
at the butterflies, but without bleaching the wings of those with
pigmentary colours.  The standard that I have set is a type and
level of lighting that will not produce significant bleaching in 50
years.  The best approach seems to be lighting that comes on for a
time (e.g. one or two minutes) at the press of a button and then
automatically turns off to a much lower level that does little more
than let the people see that the butterflies are there.  I
understand that this technique is now used in museums for the
display of rare fabrics, as an alternative to the older method of
using low light (that makes it hard to see the display). Three
questions:

    1.  Is there any objection to the general approach suggested?
        If there is, what is a better alternative?

    2.  What type of light is preferred?  I assume that radiation
        beyond visible into the lower-wavelength end is especially
        to be avoided.  Is there reason to shorten the spectrum
        still further, at the risk of losing some of the violet and
        near-violet. If the display panel will have an average daily
        illumination of one hour (probably an overestimate), what
        level of illumination is acceptable?

I realize that it may be too much to expect exact specifications to
this problem, but I am hoping that some of you have some experience
with the amount of illumination that butterflies can stand and some
suggestions on the type of lights that give the most pleasing result
for minimum bleaching risk.

Christopher K. Starr
University of the West Indies
Trinidad

                                  ***
                  Conservation DistList Instance 10:17
                 Distributed: Thursday, August 8, 1996
                       Message Id: cdl-10-17-005
                                  ***