Counter-beam lighting (German: Gegenstrahlbeleuchtung) is a type of road lighting used mainly in

road tunnels A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is usually completely enclosed except for the two portals common at each end, though there may be access and ve ...

, providing best visibility of obstacles on the

lane In road transport, a lane is part of a roadway that is designated to be used by a single line of vehicles to control and guide drivers and reduce traffic conflicts. Most public roads (highways) have at least two lanes, one for traffic in eac ...

, and thus

traffic safety Road traffic safety refers to the methods and measures, such as traffic calming, to prevent road users from being killed or seriously injured. Typical road users include pedestrians, cyclists, motorists, passengers of vehicles, and passenger ...

, while reducing light-energy cost. It is mostly installed at road tunnel entrances (transition zone) to counteract the few seconds of lower visibility while the eye adapts to new lighting conditions, which is especially impactful during sunshine and at high entry speeds. With conventional lighting technology, very high

luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls wit ...

s with correspondingly high energy costs would have to be provided in these areas to make obstacles on the roadway sufficiently visible.

Principle of counter-beam lighting

The light from the lamps does not shine perpendicularly down onto the roadway, but is angled towards oncoming vehicles. With a carefully chosen angle of inclination and suitable lighting fixtures, visibility is improved without dazzling the driver. The roadway acts as a mirror that scatters the light toward the vehicle. Since the road surface is a poor

mirror A mirror, also known as a looking glass, is an object that Reflection (physics), reflects an image. Light that bounces off a mirror forms an image of whatever is in front of it, which is then focused through the lens of the eye or a camera ...

(gray surface), the driver is not blinded, but perceives the road as a bright surface. Furthermore, any obstacle on the roadway casts a larger shadow on the road surface with this

oblique Oblique may refer to: * an alternative name for the character usually called a slash (punctuation) ( / ) *Oblique angle, in geometry * Oblique triangle, in geometry * Oblique lattice, in geometry * Oblique leaf base, a characteristic shape of the ...

incidence of light. This shadow, and the surface of the obstacle which is backlit, have a high contrast to the bright roadway. The black surface seen is larger than the obstacle itself, making it easier to perceive the hazard. With perpendicular light incidence, brighter, more expensive lamps with much higher energy requirements and greater maintenance overhead would have to be used to achieve equivalent visibility of obstacles. Therefore, counter-beam lighting can be considered an environmentally friendly contribution to road safety.

History

Contrast lighting traces its origins to the work of Ing. W. Ernst Freiburghaus (* 1921, Berne, Switzerland, † 2006, Berne, Switzerland), who was commissioned by BKW (Bernische Kraftwerke AG, today

BKW Energie BKW Energie AG (BKW; formerly known as ''Bernische Kraftwerke AG'') is a power production and distribution utility with its headquarters in Bern, Switzerland. It also provides gas and heat through a number of subsidiaries or partner companies. I ...

), Berne, Switzerland, to prepare theoretical work and practical installations (Worblaufen underpass, Bern, Switzerland) in the early 1960s. The theoretical findings were further developed and published by the Swiss Federal Office of Metrology, today

Federal Institute of Metrology The Federal Institute of Metrology (METAS) is the Swiss national metrology organization. It is part of the Federal Department of Justice and Police. Notes References External links * Standards organisations in Switzerland Feder ...

, Berne, Switzerland (without crediting the author). On the basis of his developments, BKW requested by letter of February 24, 1968, the inclusion of counter-beam lighting (then called ''BKW system with oblique beam ystem BKW mit Schrägstrahlung') in the Guidelines for Public Lighting, 2nd part, Road Tunnels - and Underpasses, of the Swiss Lighting Commission, but this was rejected. Various Swiss highway tunnels have since been equipped with this lighting system (in the 1970s, for example, the Allmend Tunnel of the

motorway A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway, and expressway. Other similar terms ...

utobahnA6, the Leimern Tunnel and the Rugentunnel of the A8). The system in the Rugentunnel of the A8 was positively evaluated by the Technical Committee TC 4 of the CIE in 1980.

Standards

Counter-beam lighting is incorporated into the recommendations of the

International Commission on Illumination The International Commission on Illumination (usually abbreviated CIE for its French name Commission internationale de l'éclairage) is the international authority on light, illumination, colour, and colour spaces. It was established in 1913 a ...

and some

central Europe Central Europe is a geographical region of Europe between Eastern Europe, Eastern, Southern Europe, Southern, Western Europe, Western and Northern Europe, Northern Europe. Central Europe is known for its cultural diversity; however, countries in ...

an countries. *

: CIE, Vienna, Austria; CIE 088:2004, 1990, Guide for the Lighting of Road Tunnels and Underpasses, ISBN 978-3-901906-31-2. * Research Society für Street and Traffic Affairs Forschungsgesellschaft für Straßen- und Verkehrswesen (FGSV): Richtlinien für die Ausstattung und den Betrieb von Straßentunneln (RABT). Köln, Germany 2003. * German Institute of Norms Deutsches Institut für Normung (DIN) e.V.">Deutsches_Institut_für_Normung.html" ;"title="Deutsches Institut für Normung">Deutsches Institut für Normung (DIN) e.V. NA 058 Normenausschuss Lichttechnik (FNL): DIN 67 524-1, Beleuchtung von Straßentunnels und Unterführungen. Berlin 1987. * Swiss Association for Standardization [ Schweizerische Normen-Vereinigung (SNV)]: (PDF; 70 kB) * Austrian Research Society Street - Rail - Traffic :de:Forschungsgesellschaft Straße – Schiene – Verkehr, Forschungsgesellschaft Straße – Schiene – Verkehr: Guidelines and Rules for Road Traffic Richtlinien und Vorschriften für das Straßenwesen (RVS) 09.02.41 Beleuchtung''RVS 09.02.41 Beleuchtung''
In: ''fsv.at'', retrieved 27 June 2017.

References

{{reflist Lighting Road safety