Figure 1 shows the original Royal Town Charter of 1826 in the offices of the mayor of Pinoso and was housed at that time in a polycarbonate vitrine measuring 50 x 35 x 7.5cm.
The book which contains the Charter has a backing of leather hide tied with ribbons and the Charter itself is made of paper and featuring a royal seal.
These materials would correspond to type-3 light sensitivity according to CIE Technical Report 157 and should be limited in light exposure to 150,000 lux-hours per year.
The illumination we measured with a Testo model 540 light meter was 213 lux on an October morning in Pinoso at around 10h45.
When we plugged the numbers into our spreadsheet (see below), we realised that the present solution permitted light exposure levels of over 600,000 lux-hours per year (almost 4 times the level recommended by the CIE:157 report).
The solution we proposed was composed of an electro-optic (‘smart’) glass vitrine, which would limit the exposure to 147,000 lux-hours per year (see below).
Our solution would constrain the Charter to light exposure only 46% of the time on display, which corresponds to 1380 hours per year (or 3.78 hours per day). This is possible due to the presence-driven activation of the electro-optic glass.
These results surprised staff at Pinoso Town Council and prompted an internal review of the ideal conditions under which to place this important document.