Lighting to discover the hidden Pompeii colours: the Thermopolium of Vetutius Placidus

Archaeological heritage lighting is a stimulating challenge for designers. The need to find a balance between conservation and valorisation raises several issues in terms of systems and structures compatibility, light sources choice, light-connected damages risks prevention, security. The lighting goal in itself is hard to define: Is the light supposed to simply guarantee monuments safe visit? Or could it dare to drive people perception, highlighting specific details, trying to recreate original luminous environments, using scenographic effects or emphasizing visit itineraries? These questions can have different and inventive answers depending on the archaeological site articulation, its characteristics and its conservation status. Pompeii is one-of-a-kind archaeological site. Excavations have brought to light an almost-intact town with its houses, shops, theatres, temples, baths. People can come back in time and live ancient Romans life by visiting spaces where they lived. All of this implies a particular design approach: differently from other sites, where buildings are mostly in ruin state, in this case, lighting design is at the same time an indoor and an outdoor design. Indeed, some buildings roofs have collapsed, others have maintained their original shape or have been rebuilt. So, visitors continuous pass from outdoor to indoor spaces and vice versa, with the consequent adaptation to very different vision conditions (from photopic to mesopic or scotopic one and vice versa). All of this can create visual performance reduction (especially when the passage from a space to another is quick), diminishing the ability in perceiving and appreciating colours, with the consequent loss of some interesting buildings details, neglected because of the inappropriate light conditions. Actually, in the most cases, each space of each Pompeii building hides some treasures: extraordinary frescos of mosaics, characterized by amazing colours, unique both for their documentary and artistic value, located all around the town, even in the most unexpected places (a cubiculum or a small shop). They should be preserved and valued. The paper focuses on an ancient Pompeiian thermopolium, the so called Thermopolium of Vetutius Placidus, a sort of “snack-bar”, where hot foods and drinks were served. The space has a simple and typical structure with a room opening onto the road (the shop) and an annexed house, but an interesting stuccoed and frescoed lararium, representing the Lares, Mercury and Dionysus, is located in the shop and the triclinium is decorated according to the third style. Thermopolium lighting conditions were analysed through illuminance, luminance and spectral power distribution measurements. Moreover frescoes colours were described by means of spectral reflectances measurements and the chromatic coordinates under different sources were calculated. All collected data are useful to drive technical choices in order to design the lighting system