Street lighting basics: poles, spacing and light levels

Street lighting is more than lighting a road: drivers' and pedestrians' vision, pole height and spacing, glare and nearby homes all have to be considered.

A newly laid village street, an internal road in a housing development or the grounds of a factory all raise the same question: how many poles, how tall, and with which fittings? A ready-made answer such as one pole every 20 metres is tempting, but the result is often either dark patches or wasted light. Street lighting is an engineering task that requires calculation, yet understanding its basic logic helps the client ask the right questions.

Who the light is for

The first step is to establish who uses the road and how. The European standard EN 13201 classifies streets on that basis:

• for fast traffic routes, the main criterion is road surface luminance, because drivers need to see obstacles against the background from a distance;
• for junctions, roundabouts and mixed-use areas, illuminance is measured;
• for footpaths, courtyards and residential streets, lower requirements apply, but recognising faces and a sense of safety matter.

In Azerbaijan, projects are based on local regulatory documents, and which ones apply is decided by the designer or the relevant authority. Either way, the higher the class, the stricter the requirements for light level and uniformity.

Pole height and spacing

Pole height and the distance between poles are linked. Light from a tall pole spreads over a wider area, so poles can be spaced further apart; short poles have to be closer together. In practice spacing is often chosen as a few times the pole height, but the exact ratio depends on the optics of the fitting and the width of the road.

When spacing is too wide, dark patches appear between poles. For drivers this alternation of light and dark is tiring, and pedestrians become invisible in the dark stretches. That is why calculations look not only at the average light level but also at uniformity, the ratio of the minimum to the average.

The arrangement of poles also depends on road width. A single-sided layout is enough for a narrow street, while wide roads use a staggered or opposite arrangement on both sides. Junctions and pedestrian crossings usually need an extra light point.

Fittings and optics

Modern LED street lights have lenses that spread light in an elongated pattern along the road rather than in a circle. This directs light onto the road surface and reduces what reaches house windows and the sky. Old globe-shaped park lanterns, by contrast, scatter a large share of their light upwards and sideways.

When choosing a fitting, check:

• whether the light distribution suits the width of the road;
• whether it emits any light upwards when mounted horizontally;
• the ingress protection rating against moisture and dust, and impact resistance;
• protection against lightning and mains surges;
• how easy it is to service the driver and optics.

Colour, glare and neighbours

Streets usually get light between 3000K and 4000K. Warmer light is more comfortable in residential areas and has less effect on the night sky and wildlife; neutral light slightly improves visual contrast on faster roads. Very cool, bluish light looks harsh and unsettling in residential streets.

Glare matters for driver safety. When a fitting is tilted too far or appears as a very bright point, drivers struggle to see into the darker zones. Next to housing, optics that emit no light backwards are chosen so that light does not fall into bedroom windows.

Control and operation

The simplest way to control street lighting is a photocell or an astronomical timer. On streets where traffic falls off after midnight, lights are also dimmed to a set level. Such decisions must be made together with safety requirements.

Maintenance should be planned in advance too: can the poles be reached with a lift, how are the cable runs protected, how will a failed light be detected? Some projects use remote monitoring systems for this.

Among the Zəfər İşığı products made in Ganja are high-output lamps meant for large areas. For a street project, however, fittings and optics must always be selected on the basis of a lighting calculation.