A demonstrator of our solar collection system was installed in a prestigious museum in Florence to provide illumination inside several large showcases. The width of the showcases can be 5m or 2m, while the height is 3m. The photos of Fig. 21 present two 5m X 3m showcases: the pictures show the showcases before (left) and after (right) the installation of the solar lighting plant. The installation of the lighting terminations within the showcases was realised in the occasion of a re-styling of the exposition showcases, with displacement
Fig. 21. Two museum showcases without (left) and with (right) the internal lighting supplied by the installed solar plant.
of the shelves and consequent new arrangement of the exhibit items (particularly evident in the lower pictures). The museum plant demonstrator included two separated installations: five devices were placed on the museum roof (Fig. 15a) and four devices were located in the garden. The roof devices were devoted to supply internal illumination in a room of the museum; while the garden installation had didactic purposes.
Each device (in Fig. 14) included eight solar lenses (in Fig. 16), coupled to eight fibre bundles, each of which had seven fibre terminations. The plastic optical fibres transported the light, concentrated by the solar collectors, within the showcases realising the lighting points that are suitably distributed within the spaces to be lighted. The total number of lighting terminations was 5x8x7=280 (from 5 devices with 8 collectors each and 7 terminations in every fibre bundle).
Museum illumination had several fundamental requirements on: illuminance depending on the exhibit items; equivalence between the two lighting types (solar light and LED); light colour and uniformity. Lighting hue and colour balance have been examined in Sect. 5.5, where photometric and colorimetric measurements have determined the appropriate filters for LED emission and light guided by plastic fibres. The museum experts indicated 100+120 lx as average illuminance required to light the showcase interior. This value took into account the illuminance levels recommended by the International Council of Museum . The exhibition objects were basically weapons, armatures and metallic objects: items made of metal, stone and ceramic have no limits on maximum illuminance; but some exposed objects were made of leather or wood and others contained horn, bone or ivory and for these materials the illuminance limit is 150 lx. The more fragile exhibit items were costumes and textiles that should not receive illumination higher than 50 lx.
The two lighting configurations, with plastic fibres or LED, were separately estimated and practically experimented directly within the showcases to individuate the best arrangement of the lighting points. The vertical positioning of the lighting spots improved the light uniformity, with respect to the horizontal positioning. The total emission angle was about 120° for LED and around 60° for the plastic fibre (numerical aperture NA=0.48) thus the LED lighting achieved a higher distribution inside the showcases. On the other hand, fibre terminations could be orientated to maximise the uniformity of lighting distribution. The selected fibres disposition and LED arrangement fulfilled illuminance correspondence and illuminance level requirements. The illuminance measured on the showcase background resulted to be between 80 lx and 170 lx; the employed luxmeter had an error of 2% ±1 digit. The solar illuminance within the showcases obviously depended on the external sunlight irradiation, which presented daily and monthly variations. This effect introduced fluctuations in the solar illuminance provided by the fibres, but the illuminance variations were judged compatible with the requirements of museum lighting.