Light reducing film for light box

Susi Pancaldo <s.pancaldo [at] ucl__ac__uk> writes

>I am looking into ways of reducing lux levels for a light-box
>display of microscope specimens from approximately 950 lux to,
>ideally, 50 lux.  The lights in the light-boxes are LED so I am not
>concerned with UV levels, just light intensity. ...

The first thing you need to do is to try to determine the
sensitivity of displayed specimens to light degradation.That being
done (or not), you have to determine the duration of the exhibition
(you didn't mention whether it is a permanent or temporary setup).
With this information you would probably want to rethink your set
goal of 50 lux. For instance, if you have specimens which do fall
into the category of very sensitive materials, which means they have
an annual limit of light exposure of 15.000 lx h/year, they could be
displayed for one month at 50 lux. However, if the exhibition lasts
only 2 weeks (which is rarely the case) you could display them at
100 lux to stay in the desired light dosage of 15.000 lx h/year. For
permanent displays there is no way to achieve this limit on a yearly
basis (for very sensitive items) except by drastically reducing
exposure times. The only way to do this is by installing the switch
which the visitors will operate to turn the lights on for a limited
number of seconds or minutes. This could easily reduce the exposure
time from 10 hours/day to 1 or even less, making it possible to
display objects for a whole year at 50 lx.

Another issue is the visibility of specimens at 50 lux. The
sensitive materials will definitely fade under light, even at 50
lux, so you could at least make sure the visitors will be pleased
with their experience by enabling them to fully enjoy the message
transmitted by the objects. So yes, maybe you must acknowledge
certain loss of the object if the visibility demands it, but it must
be kept at the satisfactory minimum. Therefore, you need to do some
experimenting with different levels of illumination from light-boxes
and determine the minimum for clear view of what is being displayed.
You can do this by applying several layers of neutral density
filters which reduce light transmission by even 50% each without
changing the hue. You may end up with thick artificial screen on
your light-boxes so you can also investigate the possibility of
installing the dimmer switches. This will definitely solve your
problem but the CCT (correlated colour temperature) will shift
slightly to the warmer region.

Veljko Dzikic
Conservator
Centre for preventive conservation "Diana"
Central Institute for Conservation in Belgrade
Terazije 26
11000 Belgrade
Serbia
+381 11 3623042
+381 64 8389896


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                  Conservation DistList Instance 27:10
                  Distributed: Monday, August 26, 2013
                       Message Id: cdl-27-10-002
                                  ***