Study of a daylight 'filter' zone in tunnels

In tunnels high energy consumption is required for guarantying the visual adaptation to the light contrast between daylight and tunnel luminance. The opportunity to graduate daylight in the threshold zone could create an area of adaptation of the human eye to the tunnel' s interior luminance, reducing consumption. In this paper a daylight “filter” structure, called pre-tunnel, is placed before the tunnel's portal, to investigate how a gradual reduction of luminance maintaining uniformity could be achieved; the structure presents very small circular holes on the ceiling giving access to natural light. A scale model has been constructed to test the effect of different diameters of holes on luminance and to evaluate the reduction of the lighting percentage. Results show the ability of this solution to have a potential control daylight management at the entrance of the tunnel.