Tunnel solutions for the light sensors - Monitoring and Testing
According to the International Committee on Illumination CIE recommendations, luminance should be monitored as the luminance contained within in a conical field of view, subtending an angle of 20º. It is recommended that a luminance photometer is mounted in the tunnel approach road approximately 120 - 200 metres from the portal, depending on the approach speed of the vehicles and their stopping distance. The purpose of monitoring the luminance at the portal is to adjust the level of light intensity inside the road tunnel to the light intensity outside so that drivers do not have to adjust their eyes quickly or become affected by the “black hole” effect where they decelerate rapidly and become a hazard to other road users.
CODEL offer the TunnelTech 601 luminance photometer for this application; it calibrated over a range of 0-6500 cd/m2 using standard traceable to the UK National Physical Laboratory. It has a thermostatically controlled heater to prevent condensation on the window and has an optional automatic window cleaning system.
In order to ensure that the light levels within the tunnel match those outside, Illuminance monitors are sited down the tunnel to control the tunnel lighting. Secondly, once inside the tunnel, as the driver's vision becomes adapted to lower lighting levels, the artificial lighting levels can be reduced in intensity as the distance travelled within the tunnel increases, a relationship known as the “Luminance Reduction Curve.
The TunnelTech 602 Illuminance photometers monitor the lighting levels along the length of the tunnel and ensure the levels are regulated in line with “Luminance Reduction Curve”.