Renovating outdoor lighting: luminaires and lighting management

octobre 2021

Agence pour l’Environnement et la Maîtrise de l’Energie (ADEME)

À télécharger : ademe-eclairage-exterieur-2021.pdf (3,9 Mio)

Luminaires

A luminaire is a device that distributes, filters, transforms and directs the luminous flux emitted by the light source(s) it contains and protects. It has aesthetic, mechanical, electrical and optical characteristics that are essential criteria in the lighting project.

A. Types of luminaires

There are several families of luminaires, depending on the type of installation and the lighting method chosen:

• Luminaires on masts or on frontage brackets: 3 to 5 m high for lighting squares and pedestrian areas; and over 5 m high for lighting streets and roads;

• bollards and columns: bollards rarely exceed 1m in height and are mainly used to punctuate pedestrian walkways; columns can illuminate larger spaces;

• wall lights: for lighting building facades or entrances;

• spotlights: from small luminaires to be placed on the ground or installed on buildings (sometimes also on masts) to highlight architectural details, to high-powered luminaires, the choice is wide and depends on the application;

• ground recessed luminaires: intended more for marking and guidance and heritage enhancement, in cases authorised by the December 2018 Order.

B. Luminaire characteristics

The photometry of the luminaire, represented by the distribution of its luminous intensities (in candelas per kilolumen: cd/klm) according to different planes, indicates in which directions and with what intensity the luminaire lights. The energy or luminous efficacy of the luminaire corresponds to its capacity to produce light for one watt consumed. It is expressed in lumens per watt (lm/W). The total efficiency of the luminaire is its ability to return the light produced by the light source it contains. Most luminaires are equipped with a control gear to operate their source: ballast or driver (for LEDs). Electronic control gear, which incorporates a control function, enables efficient management of the lighting: detection, dimming, lighting scenarios.

In terms of efficiency and life span, the new light sources now outperform all the old technologies. The most effective way to reduce operating costs is to provide a solution with demand-responsive management that reduces both energy consumption and maintenance costs. Depending on the type, LED luminaires offer a service life of 50,000 to 100,000 hours. For long-term outdoor use, a luminaire must be resistant to dust and moisture penetration, i.e. at least IP55, and usually IP65 or IP66.

C. The LED Charter

The LED Charter, proposed by the Syndicat de l’éclairage and the Fédération de la distribution de matériel électrique, is an open reference document that enables the real performance of the luminaires offered by suppliers to be compared. It gives twenty essential criteria for assessing their quality and reliability. Each criterion is defined as simply as possible with a reference to the precise paragraph of the technical standard that must be used by the manufacturer to indicate the performance level of his product. For outdoor luminaires, these are the following criteria:

1. The total initial luminous flux from the luminaire with its optic, in lumens (lm).

2. The total power of the luminaire P in watts (W).

3. The luminous efficacy in lumens per watt (lm/W)

4. The photometric curve of the luminaire (luminous intensity distribution which gives values in candelas (cd), or candelas / 1000 lm).

5. The maximum intensity value(s) in candelas (cd);

6. The rated ambient operating temperature related to the performance of the luminaire tq, in °C.

7. The luminous flux maintenance factor x, in %.

8. The median useful life LXX, in hours.

9. The initial spread of trichromatic coordinates expressed in levels of MacAdam ellipses (or SDCM, for Standard Deviation Colour Matching, which qualifies the colour homogeneity of the light of a type of luminaire).

10. The proximal colour temperature in Kelvin (K).

11. The colour rendering index (CRI, or Ra).

12. Standby power, for luminaires with sensors and detectors, in watts (W).

13. The maximum rated ambient operating temperature ta, in °C

14. The blue light photobiological risk group to which the luminaire belongs.

15. The power factor of the power supply unit.

16. The IP rating.

17. Total Harmonic Distortion (THDi).

18. IK is rated on a scale of 0 to 10, depending on the impact energy, which can range from 0 to 20 joules.

19. The proportion of light emitted above the horizontal (Upward Light Ratio) ULR.

20. CIE flux code 3.

D. Stand-alone solar luminaires

Solar luminaires are lighting devices that operate on solar energy collected during the day by photovoltaic panels. This energy, stored in a battery, is released at night to power the LED lights. The solar panel can act as a twilight cell to trigger the lighting of the luminaire. This operation (production + storage + consumption of energy) requires electronic management in order to optimise the system’s performance and rationalise energy consumption. Autonomous solar lighting, i.e. not connected to the electricity grid, is all the more relevant economically when the grid is defective or even absent. These complex, well-dimensioned systems can be used for many lighting situations. The luminaires are subject to the same normative and regulatory requirements as those connected to the electricity grid. Solar lighting must be sufficient to achieve the recommended illuminance levels in the area to be lit. This requires a study of the amount of sunlight and the level of use: the system allows the lighting profile to be adapted to actual needs. With hybrid systems (both grid and solar), lighting levels are maintained throughout the night, as the power supply switches to the grid during the night. However, these systems, which combine the two modes of power supply, must be correctly sized to minimise their environmental impact.

a) Batteries

There are three types of battery technologies used for stand-alone solar street lights. The choice depends on several factors such as outdoor temperature, battery ventilation, etc. :

• Lead-acid: not recommended, as they have a low efficiency and use a lot of material due to a limited range of use, and should be replaced every 5 to 6 years;

• NiMH (nickel metal hydride): the greater useful capacity makes it possible to reduce the size of the batteries, which can operate at extreme temperatures (from -40° to +70°);

• LiFePO 4 (lithium iron phosphate): these batteries can accept high depths of discharge while maintaining their life span.

The number of possible charge-discharge cycles depends on the depth of discharge (minimum percentage of energy remaining) at each cycle. The depths of discharge accepted by NiMH and LiFePO4 batteries are much greater than for lead-acid batteries. Luminaires equipped with these batteries do not require heavy maintenance for several years.

b) Panel sizing

The solar lighting project requires a good knowledge of the duration of use of the luminaire. Indeed, it is not enough to know that a certain power is needed per luminaire, it is essential to know the duration of the lighting of the luminaire in order to size the photovoltaic panel. For example, we calculate that we need 100 Wh of energy per night (20 W of power for 5 hours, or 2 hours at 100% and 6 hours at 50%).

If the luminaire is to have three days of autonomy, the battery must be able to store 100 Wh x 3, i.e. 300 Wh. Depending on the battery technology and its efficiency, the total amount of energy required can be deduced. Since the solar panel loses about 0.8% of its power per year, it is customary to oversize it from the outset to compensate for the energy lost over time and allow the solar panel to produce the same amount of energy after 25 years.

Sizing software can be used to calculate the size of the solar panels according to the geographical location of the city: it is recommended to make the calculations based on the amount of sunshine in December. In addition, the inclination of the panel is also an important element to take into account to ensure sufficient energy production all year round.

In some cases, it may be appropriate to accept a reduced service rate depending on the battery charge, for example to preserve the battery’s life span. This should be done in transparency and consultation with the community.

Lighting management

The technological transition, in particular towards LEDs, has brought electronics at all levels: power supply, protection, light source (allowing variation of intensity and colour temperatures), detection, and has integrated connectivity which offers the possibility of adding communicating systems.

The implementation of these tools must be simple for the distributor and the installer who will program the maintenance and for the diagnosis in case of failure. These tools range from small smartphone applications that scan the driver to very sophisticated management systems. It is important that renovation operations are carried out as far as possible with upgradable luminaires. Switching to more efficient sources already generates at least 40% savings (average gains observed for LEDs). To achieve maximum energy savings, presence-detecting systems can be added.

In addition, these dis- positives make it possible to meet the requirements of the December 2018 decree on light pollution and the quality of the night sky and go hand in hand with environmental conservation. An ageing installation, using old technology sources and switched off for a few hours a night, will always consume more overall than an installation using today’s most efficient sources, equipped with photometry that reduces light nuisance, and provided with management devices, with presence detection, for example.

A. The different management functions

The challenge is to find the right level of intelligence for each context. Therefore, in the same town, the answers are always mixed.

• Switching on and off can be done with an astronomical clock or a luminosity detection system.

• The driver or ballast can be set for dimming in the middle of the night, for example, to 100% at the beginning and end of the night, and with plateaus at lower levels at intermediate times.

• Presence detection, especially on cycle paths or areas with pedestrian traffic.

• Group function: a set of luminaires that communicate with each other, e.g. one luminaire is able to send a signal to a neighbouring luminaire to indicate that it has detected a presence, and so on, to illuminate a whole area. Through parameterisation, groups can be created and lighting scenarios defined. This function is deployed in places where there are conflicts between biodiversity and human uses and therefore often linked to sensors (along a canal, in a park, etc.), or in connection with mobility routes (tramway accompaniment, cycle paths).

• The pooling of sensors and communicating systems makes it possible to further reduce operating costs and to facilitate the deployment of these technologies in order to make them relevant to users, who must be accompanied by sufficient light to see and be seen. Careful thought and planning by the owners are needed to achieve this level.

B. From intelligent lighting to intelligent territories

The intelligent city is first and foremost one that is correctly lit, where and when it is needed. Today’s technology makes this possible: with sensors, presence detectors and dimming systems that offer the possibility of lowering the lighting level in standby mode and raising it to a level of use when movement is detected, whether it be the passage of a person or a vehicle.

At this level of management, there are automatic controls specific to lighting, for example :

• collecting data for maintenance and operation;

• comparing different zones to refine management;

• programming systems remotely and controlling them according to events (Bastille Day, Fête de la musique, Museum Night, etc.) or according to certain constraints, or to reinforce safety in the event of difficult weather conditions, traffic jams or accidents.

But it is also possible to add functionalities that take into account other services at the city level. As soon as the luminaire is connected and able to send information back to a secure gateway, the luminaire can collect this useful data (traffic measurement, for example). It is now essential to take into account digital security requirements in accordance with the European Cybersecurity Act and to choose systems that are connected by design to protect against malicious acts.

The dense and meshed infrastructure of street lighting poles and lampposts allows for other digital applications, especially as it benefits from a dedicated electrical network.

For example, it is possible to integrate a communication relay antenna on a lamppost; the mast can also accommodate air sensors, loudspeakers, surveillance cameras, etc., all connected elements that would normally require the installation of additional supports.

These bridges to other uses go beyond the purely lighting domain but consider the mast as a support that offers new services. The design of such installations is done in a transversal way between different professions. The network thus created constitutes a communication infrastructure for all the sensors of the intelligent city of tomorrow.

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