Renovating public lighting: what a municipality must check

The town council has voted a budget to replace the lanterns on the main street. Before comparing models, two questions decide the real budget: how many columns are still sound, and what does the cable that supplies them carry.

The lantern accounts for only part of the cost of a public lighting renovation. Supports, networks and control cabinets make up the rest, and they are the ones that cause unpleasant surprises during the works.

Inventorying the existing installation: columns, cables, cabinets

The inventory comes before the programme. It is built light point by light point, with physical numbering transferred onto a georeferenced plan. Each record gives the location, height, type of support, type of source, power and observed condition.

Control cabinets are surveyed separately. The survey covers residual current protection, the rating of the outgoing circuits, the control mode, the presence of a time switch and the associated metering point. An obsolete cabinet rules out installing remote management, whatever luminaire is chosen.

Networks are the hardest item to assess. An overhead network can be seen, an underground network is deduced from plans and insulation measurements. The cross-section of the conductors directly determines whether new light points can be connected without replacing the cable.

This inventory is the document that then serves for everything: tendering, funding applications, multi-year planning. An on-site lighting audit produces this survey in a form that can be used directly in a public procurement procedure.

Road classes and levels expected by the road lighting standard

The EN 13201 standard structures the sizing of public lighting. It begins by classifying each road according to its speed, traffic and the presence of pedestrians and cyclists, then assigns a lighting class.

M classes apply to motorised traffic routes and are sized in road surface luminance, from 2 candelas per square metre for class M1 to 0.3 candela per square metre for class M6. C classes deal with conflict areas, junctions and roundabouts. P classes apply to pedestrian areas and low-speed roads, and are sized in illuminance.

| EN 13201 class | Maintained average illuminance | Minimum illuminance |

| --- | --- | --- |

| P1 | 15 lux | 3 lux |

| P2 | 10 lux | 2 lux |

| P3 | 7.5 lux | 1.5 lux |

| P4 | 5 lux | 1 lux |

| P5 | 3 lux | 0.6 lux |

| P6 | 2 lux | 0.4 lux |

Classifying roads is as much a planning decision as a technical one. Dropping one class on a residential street reduces installed power and nuisance for residents, provided pedestrian crossings and junctions are still treated as conflict areas.

Condition of the supports: the most often underestimated point

A public lighting column is a structure subject to wind, designed according to the NF EN 40 series of standards. Its service life depends above all on its base, at the interface with the foundation, where moisture stagnates and corrosion progresses unseen.

The check is made by local stripping and probing at the embedding point, supplemented if necessary by a thickness measurement. A column corroded at the base is not reused, even if its upper part looks sound. Inspection doors, brackets and foundations are checked during the same visit.

One check is systematically forgotten: the mechanical compatibility of the new luminaire with the support. Its weight and wind surface must remain within the limits of the original design calculation. A larger luminaire on an old column can take the structure outside its range of validity.

Choosing the street luminaire and its mounting plate

Once the supports have been qualified, the luminaire is chosen on criteria that can be verified on the data sheet:

• The photometric class and the availability of the IES or LDT file, essential for the calculation under EN 13201.
• The IP rating, IP66 being the usual benchmark for street lighting, and the IK rating suited to the mounting height.
• Class II electrical insulation, which avoids having to redo earth connections on old networks.
• Surge protection, particularly on overhead networks and in storm-prone areas.
• A dimmable driver and, where applicable, a standardised interface for a remote management module.
• The accepted spigot diameter and the adjustable tilt of the mounting plate.

The fixing point deserves particular attention. Column tops and brackets exist in several diameters, and the adapter is ordered with the luminaire. The actual tilt after installation determines both the photometry and compliance with the upward light ratio.

The choice is then made by road family, limiting the number of references selected. Outdoor and street lighting luminaires and equipment for traffic routes come in several power ratings on the same mounting plate, which simplifies management of the maintenance stock.

Power reduction and astronomical clock

A municipality lights a road several hours a night even though traffic becomes negligible after a certain time. Three devices can be combined depending on the level of equipment required.

The astronomical clock calculates sunrise and sunset from the municipality's coordinates and controls switching without seasonal drift. It is a worthwhile replacement for a dirty or poorly oriented photocell.

Power reduction programmed into the driver applies a time profile, without any additional control link. It is the simplest solution for a gradual extension of the installation.

Switching off in the middle of the night, decided by municipal order, produces the clearest saving. It requires prior consultation, appropriate signage at junctions and information for residents. These three devices are documented in the operating file, with the time profile chosen for each sector.

Light pollution and colour temperature in residential areas

The French order of 27 December 2018 on the prevention of light pollution applies to public lighting. It caps the proportion of flux emitted above the horizontal, with a value of 4 per cent for ordinary lighting and a stricter requirement in protected natural areas.

Colour temperature is also regulated: 3000 kelvins maximum as a general rule, with lower thresholds in natural areas and near astronomical observation sites. In practice, warm shades are better accepted in residential areas and reduce the attraction of nocturnal insects.

This aspect is dealt with at the same time as road classification, because the two are linked. A check of the regulatory compliance of the installation makes it possible to fix these parameters before the specifications are drawn up.

Project stages and the parties to bring together

1. Carry out the inventory of the installation and the survey of the cabinets, with georeferencing.
2. Classify the roads under EN 13201 and set the target levels for each sector.
3. Have the mechanical condition of the columns and foundations checked.
4. Define the multi-year programme and the phasing by district or by street.
5. Check which body holds the competence: departmental energy syndicate or the municipality directly.
6. Examine the available funding, including the standardised scheme RES-EC-104 for the renovation of outdoor lighting, the only scheme still open for this item.
7. Draw up the specifications with the photometric criteria and compliance requirements.
8. Plan acceptance with on-site measurements and handover of the operating file.

The first milestone is the most decisive: start the survey of the installation before the next budget is prepared, so as to have a substantiated cost estimate at the time of the vote.

Luminaires for roads and public spaces are grouped in the outdoor and street lighting category, together with the associated control equipment.