Luminance measurement

The requirements for tunnel lighting are determined by the nature of the human eye. How well the eye recognises vehicles and other obstacles in a tunnel depends on the lighting and visibility as well as the reflexion characteristics of the road surface and the tunnel walls. Tunnel lighting needs to be adapted to these environmental conditions.

The tunnel lighting must be controlled such that users, both during the day and by night, can approach, pass through and exit the tunnel without changing direction or speed with a degree of safety equal to that on the approach road. Especially the lighting of a tunnel entrance should be adequate to avoid the “black hole effect” when a driver enters the tunnel.

Luminance is the measure representing what a human being perceives as brightness and as such is the main control variable for the tunnel lighting.

Several international and national guidelines and standard describe how to design and control tunnel lighting:

  • CIE 88:2004 Guide for the lighting of road tunnels and underpasses
  • CEN Report CR 14380 Lighting applications – Tunnel lighting
  • DIN 67524 Beleuchtung von Straßentunneln und Unterführungen (DE)
  • RVS 09.02.41 Tunnelausrüstung Lichttechnik Beleuchtung (AT)

If a measurement of luminaces is indicated luminance meters are used in front of the portal and where required also inside the tunnel.

The luminance photometer comes with a zoom lens that is focussed to measure the relevant area. Light from this area through the lens is directed to the photo element detecting its intensity. The integrated evaluation unit then calculates the luminance and provides it through the analogue output(s).

Request a quote

Would you like to request a quote for any of our products or services?

Please click below and leave your details. We will contact you as soon as possible.

t/LUM-A Luminance meter

  • Zoom lens to adjust the focus areas
  • Sensor with V(λ) filter and silicon photo element
  • Temperature compensated and long term stable amplifier for the photoelectric current using live zero
  • Heated housing with protection class IP65 either made of polycarbonate or stainless steel 1.4571
  • Electronically controlled heating and temperature monitoring
  • Mounting flange to adjust horizontal and vertical angle
  • Fault indication by relay isolated contact (NC)
  • Optional second output channel for increased resolution at low lighting levels
  • Surge protection
  • Luminance meter to measure the luminance in the access zone L20 mounted on a pole in front of the tunnel portal or
  • Luminance meter to measure the luminance in the threshold zone Lth mounted on the tunnel wall
  • Luminance meter to measure the luminance in the interior zone Lin mounted on the tunnel wall
  • Power supply 230 or 115 VAC
  • Analogue signal outputs connected to the lighting or tunnel control system
  • Specifically designed for tunnel applications
  • Customisable measuring ranges
  • Identical luminance meter for all measuring ranges and mounting locations
  • No moving parts
  • Sensor can be replaced easily without tools
  • Housing resistant against corrosion, UV, oil und acid
Technical Specifications
Luminance photometer with 1 output channel
Model t/LUM-A1
Measured value Luminance (light density)
Measuring range 1 Customisable
typically 0 .. 10.000 cd/m² or 0 .. 6.000 cd/m²
Field angle 8° .. 34°
Analogue output(s) 1 x 4 – 20 mA
Relay contact 1 x operation/fault (NC)
Luminance photometer with 2 output channels
Model t/LUM-A2
Measured value Luminance (light density)
Measuring range 1 Customisable, typically 0 .. 500 cd/m² or 0 .. 10 cd/m²
Measuring range 2 Customisable, typically 0 .. 50 cd/m²
Field angle 8° .. 34°
Analogue output(s) 2 x 4 – 20 mA (1 per measuring range)
Relay contact 1 x operation/fault (NC)
Power supply
Operating voltage 230 VAC / 50 Hz ± 10 % (or 115 VAC / 60 Hz ± 10 %)
Power consumption approx. 50 W
Dimensions & Mounting
Dimensions 245 x 180 x 485 mm (polycarbonate)
200 x 180 x 450 mm (stainless steel)
(without mounting flange)
Protection class IP 65
Material Polycarbonate MAKROTECH UV® or
Stainless steel 1.4571 (AISI 316Ti)
(both ZTV-ING Anforderungsklasse I)
Mounting accessories (optionally) Adjustable wall mounting console,
Pole mounting console with pole clamps
Electrical standards 2006/95/EC Low Voltage Directive (LVD)
2004/108/EC Electromagnetic compatibility(EMC)
IEC 61326-1:2012
IEC 61010-1:2010
Road safety standards AT: RVS 09.02.41 2009
DE: RABT 2006
Lighting standards CIE 88:2004
CEN report CR 14380


Product info DE (PDF, 570 kB)
Product info EN (PDF, 570 kB)


Mounting locations of the luminance meters


Luminance meter L20

The luminance meter is mounted in front of the portal in stopping distance. It measures the average luminance of the visual field of the driver with an angle of view of 20°. If the luminance meter is not mounted in stopping distance from the portal the angle of view can be adjusted by the zoom lens.


Luminance meter Lth

The luminance meter is mounted on the tunnel wall and aligned on the lane. It measures the luminance Lth in the first part of the threshold zone.


Luminance meter Lin

The luminance meter is mounted on the tunnel wall and aligned on the lane. It measures the luminance Lin in the interior zone.