Minimizing lighting consumption in existing tunnels using a no-cost fine-tuning method for switching lighting stages according revised luminance levels

Visual adaptation demands increased illuminance in the tunnel entrance, which results in an increased number of installed luminaires and power consumption of each luminaire. There are norms that define the required luminance in this entrance zone, which depends on the variability of the daylight on the surfaces that surround the entrance. In most existing tunnels, at the time of their design, there were no proper simulation tools resulting in an over-dimensioned lighting system, thus leading to over illumination and increased energy consumption. The reduction of this consumption can be realized through proper optimization of the pavement or by retrofitting the lighting system with cost effective LED luminaires. However, energy savings can be achieved with proper control of the tunnel’s lighting system, since it is quite common to be organized in a number of active stages. In this paper, a non-cost fine-tuning method for switching the lighting stages according to the traffic weighted L20 luminance is proposed. The method was applied in a real –case scenario, where L20 luminance of the access zone at an existing tunnel was newly calculated. A new luminance demand value for threshold zone was calculated using the traffic weighted L20 method of CR14380. The new transition zone decreasing luminance curves were produced and compared with the existing ones. Thus, a new switching control was proposed and programed to the Supervisory Control and Data Acquisition system of the tunnel. The signal of the L20 meter for a period of two days was used and the corresponding energy consumption was calculated using the proposed switching program. The results have been compared also with a scenario were the existing lighting system was retrofitted with LED luminaires. The fine-tuning method for switching resulted in 26% and 35% energy savings concerning the existed installation with no extra cost while the energy savings by installing LED was 52% and 69% with an additional cost of LED luminaires and the corresponding labor cost for the retrofit.