The transition between day and night along with changes in weather conditions present a challenge for tunnel operators to ensure lighting in road traffic tunnels remain at safe levels for motorists at all times. The lighting control at the tunnel portals is particularly important to ensure drivers do not suffer from “black hole syndrome” whereby the drivers’ eyes aren’t able to adjust to sudden changes in light as they enter and exit a tunnel.
Luminance Photometers for Tunnels
To control the tunnel lighting the light levels must first be measured, Luminance Photometers are used to measure the level of luminance, or brightness, at the tunnel entrance and exit portals. This information is used by the tunnel’s lighting control system to ensure that the visual perception of drivers is maintained by adjusting the brightness of the tunnel’s internal lights.
The ACOEM Tunnel Sensors LUMIOS Photometer uses a specially designed, highly light-sensitive photocell, filtered to provide a spectral response close to that of the average human eye, to react to changes in light levels at the entrance and exit, as well as within the tunnel bore. This reaction is virtually instantaneous.
The light receptor measures the average luminance within a fixed viewing angle (set during manufacture) within a range of 10 to 40º. The standard instrument has an acceptance angle of 20º (as recommended by Commission Internationale de l´Eclairage (C.I.E.), publication 88, 2004). The luminance measurement range is scalable between 0 – 10,000 cd/m2.
The photometer installation point is typically at the driver’s safe stopping distance from the tunnel portal, based on the maximum road speed.
The LUMIOS-MkIII Photometer has onboard SCADA / PLC interface options, including Current Outputs, Digital Relays and RS485 (Modbus RTU). Optional wipers and pumped washer systems are also available for more demanding environmental conditions.