The technical services receive a quote for point-for-point replacement of the street lighting: same location, same height, same wattage, an LED lantern in place of the discharge lantern. The file looks simple, it goes through committee, and the town ends up with a new installation that reproduces exactly the defects of the old one.
This reflex of like-for-like replacement costs twice: in investment, because useless power is bought, and in operation, because it is then paid for every night.
Classifying the roads before choosing the luminaires
A municipal installation is not uniform. A road through the village centre, a residential street, the car park of a village hall and a footpath alongside a school call for neither the same level nor the same measured quantity.
The first part of the EN 13201 series gives the method for selecting lighting classes. It relies on objective parameters: speed limit, traffic density, presence of pedestrians and cyclists, difficulty of navigation, parked vehicles, ambient luminance of the area.
This classification work is done on a plan, with the elected officials and the technical services, before any supplier is consulted. It turns a list of light points into a document that can be used in a specification.
What the EN 13201 series brings to the file
The series distinguishes three main families of classes, which are not measured with the same physical quantity. Confusing the first two families leads to tenders where the offers cannot be compared.
Family of classes | Quantity used | Intended use |
|---|---|---|
M classes, from M1 to M6 | Average road surface luminance, expressed in candelas per square metre | Roads with motorised traffic, medium to high speeds |
C classes, from C0 to C5 | Average horizontal illuminance | Conflict areas: junctions, roundabouts, pedestrian crossings |
P classes, from P1 to P6 | Average horizontal illuminance and minimum illuminance | Pedestrian and cycle areas, residential roads |
The other parts of the series complete the system: methods for calculating performance, methods for measuring on site and energy performance indicators. These indicators are valuable in a municipal file, because they make it possible to compare two projects on a basis other than the price of the lantern.
Moving away from like-for-like replacement
The oversizing of an old installation rarely comes from excess flux at the source. It comes from the way this flux was distributed: a discharge lamp in a domed bowl sends a large share of its light above the horizontal and onto facades, so many lumens were needed to obtain the useful level on the road.
An LED optic directs the flux towards the surface to be lit and covers the same road width with noticeably lower installed power. Reproducing the old wattage cancels this benefit and creates local over-intensities, with the nuisance that goes with them.
The useful work therefore consists of recalculating the spacing, the mounting height and the type of optic from the class chosen for each road. On some stretches, the conclusion is that one point in two is enough; on others, it is that a badly placed column must be moved rather than re-equipped.
Colour temperatures and limiting light nuisance
The order of 27 December 2018 on the prevention, reduction and limitation of light nuisance governs outdoor lighting. It sets a maximum colour temperature for new installations, lowered in protected natural areas and astronomical observation sites.
It also governs the proportion of flux emitted above the horizontal, which in effect rules out lanterns with uncontrolled domed bowls. These two requirements are checked on the product data sheet, before the tender, and are explicitly restated in the specification.
The question of colour is also one of local acceptability. A warm tone is better received in old town centres and residential areas, and it limits disturbance to nocturnal wildlife along ecological corridors.
Night-time dimming and partial switch-off
Once the right levels have been chosen, the next lever is the time schedule. Power reduction in the middle of the night is programmed at driver level, by an autonomous time profile or an astronomical clock, and is set road by road rather than across the whole installation.
Complete switch-off in the middle of the night is a local political decision, taken by municipal order under the mayor’s police powers. It requires prior communication, suitable signage and an examination of sensitive points: surroundings of buildings open to the public, junctions, public transport stops, routes to housing.
A renovated installation has the advantage of making these decisions reversible. Configurable dimming makes it possible to adjust the profile after a few months of operation, with no new work on the columns.
Columns, brackets and reuse of existing supports
The lantern is the visible part of the project, but the support determines the safety and lifetime of the installation. The condition of the foundations, corrosion at the base of the column and the strength of the brackets are checked before any decision to reuse them.
A column kept imposes its mounting height and position, and therefore strongly constrains the photometric calculation. A column removed frees the calculation but adds a civil engineering line to the costing, and this trade-off is made section by section.
The same examination applies to the control cabinets, the protective devices and the condition of the network. A renovation that leaves an outdated cabinet in place simply postpones the failure by a few seasons.
Phasing the renovation over several budget years
Few towns finance the complete overhaul of an installation in a single financial year. Phasing is built by road class and by coherent sector, so as to avoid visual breaks in the middle of a street and to treat first the stretches where the gap with the target class is greatest.
This phasing requires a consolidated survey: geolocated inventory of the points, wattages, heights, types of optic, condition of the supports. That is exactly the deliverable of a lighting audit carried out in the field, which then serves as the basis for all the following phases.
The scenarios are checked by calculation with the support of a lighting design office, on the same principles as those applied in our other lighting solutions by sector. On the equipment side, the ranges of outdoor and road lighting lanterns and luminaires for traffic routes cover the usual classes of a municipal installation.
To start classifying your town’s roads and cost the first phase, request a visit of your installation.
