1 Scope This part of the European Standard defines how to calculate the energy performance indicators for road lighting installations using the calculated power density indicator PDI DP
Terms and definitions
For the purposes of this document, the terms and definitions given in EN 12665:2011 and the following apply
3.1.1 system power (of a lighting installation in a given state of operation)
P total power of the road lighting installation needed to fulfil the required lighting classes as specified in
EN 13201-2 in all the relevant sub-areas, and to operate and control the lighting installation (unit: W)
3.1.2 power density indicator PDI (of a lighting installation in a given state of operation)
The D P value of a lighting system is determined by dividing the system power by the product of the surface area to be illuminated and the calculated maintained average illuminance value for that area, as specified in EN 13201-3 The unit of measurement for this value is W.lx\(^{-1}\).m\(^{-2}\).
3.1.3 annual energy consumption indicator AECI (of a lighting installation in a specific year)
D E total electrical energy consumed by a lighting installation day and night throughout a specific year in proportion to the total area to be illuminated by the lighting installation (unit: Wh.m -2 )
The installation luminous efficacy (\( \eta_{inst} \)) is defined as the minimum luminous flux required to achieve the necessary lighting level for a designated area, divided by the total average power consumption of the lighting system, measured in lumens per watt (lm/W).
3.1.5 constant light output CLO (of a road lighting installation) regulation of the road lighting installation aiming at providing a constant light output from the light sources
Note 1 to entry: This functionality aims to compensate for the light loss caused by ageing of the light sources
The installation lighting factor, denoted as \$q_{inst}\$, is a dimensionless value that represents the relationship between the calculated average maintained luminance of a road surface and the average maintained horizontal illuminance on that surface This factor also considers the average luminance coefficient from the r-table used in luminance calculations.
Symbols and abbreviations
Symbol or abbreviation Name or description Unit
A FL Area of the left sidewalk m 2
A FR Area of the right sidewalk m 2
AECI Annual Energy Consumption Indicator
C L Correction factor for luminance or hemispherical illuminance based lighting designs - c op Lighting operation coefficient -
D E Annual energy consumption indicator (AECI) Wh.m -2
D P Power density indicator (PDI) W.lx -1 m -2
E Average maintained horizontal illuminance lx
E FL Calculated maintained illuminance on the left sidewalk lx
E FR Calculated maintained illuminance on the right sidewalk lx
Symbol or abbreviation Name or description Unit
E min Minimum required average illuminance lx
E R Calculated maintained illuminance on the carriageway lx
EIR Edge Illuminance Ratio f M Overall maintenance factor (MF) of the lighting installation - k red Reduction coefficient for the reduced level illumination -
L min Minimum required average luminance cd.m -2
LOR Light Output Ratio m Number of operation time periods for different levels of operational power P -
MF Maintenance Factor n Number of sub-areas to be lit - n lp Number of light points associated with the lighting installation or the representative section -
P System power of all the luminaires designed to lit the relevant area W
P ad Total active power of any devices not considered in the operational power P but necessary for operation of the road lighting installation W
P F System power of the luminaire designed for illumination of the sidewalk W
P ls Power of lamp(s) inside the luminaire W
P R System power of the luminaire designed for illumination of the carriegeway W PDI Power Density Indicator
R LO Optical efficiency of luminaires (LOR) used in the lighting installation - q inst Lighting factor of an installation -
The average luminance coefficient is denoted as \$Q\$, measured in sr\$^{-1}\$ The duration of operation for a specific system power \$P\$ is represented as \$t\$, calculated over a year in hours The full annual operation time at maximum illumination level is also denoted as \$t\$, while the annual operation time at a reduced illumination level is indicated as \$t_{red}\$.
The utilization of lighting installation is measured by the luminous flux (\$Φ_A\$) that reaches the illuminated area, expressed in lumens (lm) The luminous flux emitted from the light source(s) within a luminaire is denoted as \$Φ_{ls}\$ (lm) The installation's luminous efficacy (\$η_{inst}\$) is calculated in lumens per watt (lm.W^{-1}), while the luminous efficacy of the light sources used is represented as \$η_{ls}\$ (lm.W^{-1}) The number of luminaires considered in the calculation is indicated by \$n_{lu}\$, and the power efficiency of the luminaires in the lighting installation is denoted as \$η_P\$.
Calculation of the power density indicator
Power density indicator for an area divided into sub-areas for a given state of operation shall be calculated with the following formula:
D P is the power density indicator, Wãlx -1 ãm -2 ;
P is the system power of the lighting installation used to light the relevant areas (see 4.3), in W;
E i is the maintained average horizontal illuminance of the sub-area “i” determined in accordance with 4.2, in lx;
A i is the size of the sub-area “i” lit by the lighting installation, in m 2 ; n is the number of sub-areas to be lit
When lighting class requirements vary throughout the night or across seasons—such as reductions due to lower traffic density or changes in the visual environment—the power density (D P) must be calculated individually for each lighting class Alternatively, if multiple lighting classes are utilized during the night or year, an average power density (D P) can be computed for the entire period It is essential to clearly outline the assumptions made in the calculation of power density (D P) and the methodology used to derive this value.
Values of the power density indicator (D P) shall be always presented and used together with the annual energy consumption indicator (D E) for assessment of the energy performance of a particular lighting system.
Average horizontal illuminance to be used for calculation of the power density
For illuminance based lighting classes (C and P) the maintained average horizontal illuminance (E) to be used for the power density (D P) calculation shall be calculated according to EN 13201-3
For luminance-based lighting classes (M), the average horizontal illuminance (E) used for calculating power density (D P) must be derived from the average illuminance values obtained from the same grid points utilized for luminance calculations, as specified in EN 13201-3.
For hemispherical illuminance-based lighting classes (HS), the maintained average horizontal illuminance (E) used for power density (D P) calculations must be the average of illuminance values derived from the same grid points utilized for calculating hemispherical illuminance, as specified in EN 13201-3.
Over lighting in lighting installations can lead to significantly higher levels of illumination than necessary It is essential to assess whether this over lighting stems from poor design or is an unavoidable outcome of other requirements To promote energy efficiency and protect the environment, corrective measures should be implemented to reduce any excessive lighting.
To enhance energy efficiency and minimize environmental impact, the lighting level for any installation should not surpass the required level of the next higher lighting class, or exceed the maximum level by 50% for the highest class, without taking into account alternative design solutions.
System power (P) to be used for calculation of the power density indicator
The system power (P) is determined by summing the operational power of light sources, control gear, and other electrical devices directly linked to the lighting installation This includes lighting point control units, switches, and photoelectric cells To accurately calculate the system power, it should encompass the entire lighting installation or a representative section utilized in the lighting design, following the specified formula: p k ad.
P is the total system power of the lighting installation or its representative section, in W;
The operational power, denoted as \$P_k\$, refers to the power consumption of the 'k-th' lighting point, which includes light sources, gear, and other associated devices such as lighting point control units, switches, or photoelectric cells essential for its functionality, measured in watts (W).
P ad represents the total operational power required for devices essential to the functioning of road installations, excluding P k This includes components such as remote switches, photoelectric cells, centralized luminous flux controllers, and centralized management systems, measured in watts (W).
To calculate the system power for a specific area, the total operational power \( P_{ad} \) should be distributed based on the ratio of the number of luminaires used for illumination to the total number of luminaires supplied by the devices represented by \( P_{ad} \) The variable \( n_{lp} \) denotes the number of lighting points related to the lighting installation or the representative section utilized in the calculation.
If light sources (and other electrical devices) are operated on constant power, this power shall be used when the system power (P) is calculated
When the lighting class varies throughout the night or across different seasons—such as a decrease in lighting class at night due to lower traffic density or changes in the visual environment—the system power (P) needed for the appropriate lighting class during that time must be accurately calculated.
PDI can either be a single value for full-time constant power operation at 100% dimming level in regulated systems, or it may vary for each operational state For detailed calculations, refer to Annex A, while Annex D provides an example of how to present the results.
To calculate power density (D P) in lighting systems with varying luminous flux output, it is essential to consider the average system power associated with these fluctuations This is particularly relevant for light sources utilizing constant light output (CLO) drivers, which adjust their luminous flux over time to maintain consistent performance.
When calculating the main lighting class for a road section, it is essential to consider a typical arrangement and spacing The system power (P) must account for the total power of all luminaires and associated electrical devices, in accordance with EN 13201-3 Annex A provides typical examples to illustrate this Additionally, the number of luminaires should be appropriately matched to the size of the area being illuminated.
To calculate the system power (P) for an irregularly shaped area, it is essential to sum the power of each luminaire along with the electrical devices associated with the luminaires, lighting points, and segments required to adequately illuminate the space.
The system power (P) must exclude any power from devices not utilized for lighting purposes, even if they are part of the same network Common examples of such devices include illuminated advertisements and festive lighting.
Area (A) to be used for calculation of the power density indicator
The area utilized for calculating the power density indicator (D P) must match the area employed in lighting design for parameter calculations as per EN 13201-2.
When calculating the Edge Illuminance Ratio (EIR) for a road's carriageway that is not bordered by other areas with specific lighting requirements, such as footpaths or parking areas, the surrounding areas are excluded from the power density indicator calculation as per EN 13201-2 standards.
5 Annual Energy Consumption Indicator (AECI)
The annual electricity consumption of a road lighting installation depends on:
— the period of time for which lighting is provided,
— the lighting class specified by the relevant lighting standard for each lighting period,
— the efficiency of the lighting installation, when providing the necessary lighting for each period,
— the way the lighting management system follows the change in visual needs of road users,
— the parasitic energy consumption of lighting devices during the period when the lighting is not needed
To effectively compare and monitor the energy performance of a lighting installation, it is essential to consider the annual accumulated energy consumption of road lighting in public areas However, actual lighting requirements may fluctuate throughout the year due to various factors.
— seasonal variations of daylight / night time hours: this depends on the geographical location of the area,
— changing weather conditions which influence perceived visual performance (i.e dry or wet road surface),
Traffic density in streets and public areas varies significantly at night, influenced by distinct usage patterns such as heightened activity during rush hours Additionally, fluctuations in social activities, including school terms and national holidays, further impact these traffic dynamics.
— changing functionality of the street or public area (i.e roads are closed for a certain period or turned to pedestrian areas in festive seasons)
Annual energy consumption indicator (AECI) shall be calculated with the following formula: j j
D E is the annual energy consumption indicator for a road lighting installation, in Wh.m -2 ;
P j is the operational power associated with the j th period of operation, in W; t j is the duration of j th period of operation profile when the power P j is consumed, over a year, in h;
The area illuminated by a specific lighting arrangement is denoted as A (in m²), while m represents the number of periods with varying operational power P_j Additionally, m includes the duration during which quiescent power is utilized, typically encompassing daylight hours and any nighttime periods when the lighting is off.
To ensure a consistent light output from a light source, it is essential to account for variations in power consumption over time, particularly when using constant light output (CLO) drivers The average power consumption throughout the expected lifespan must be factored into the calculations Additionally, the calculations should explicitly state the lifetime assumptions made and the methodology used to determine the average consumption value.
Annual energy consumption indicator (D E) shall be always presented and used together with the values of the power density indicator (D P) for assessment of the energy performance of a particular lighting system
Examples of calculation and typical values of energy performance indicators
Examples of operational profiles
General
Daily operational profiles for road lighting vary throughout the year, influenced by geographical latitude and local conditions, with changes in start and end times of operation.
The operation of artificial lighting should align with daylight illuminance levels, adhering to the requirements of EN 13201-2 for specific lighting classes During sunset, illuminance levels are initially high but decrease quickly, while the opposite occurs at sunrise.
This annex provides examples of operational profiles that demonstrate the daily variations in lighting levels The power level required for calculating energy performance is linked to these lighting levels, which are influenced by factors such as lamp type and lamp power.
NOTE 1 This annex does not deal with particular relation between lighting level and power level
For the calculation of AECI it is necessary to sum up daily operation hours for each of the lighting levels throughout a whole year
NOTE 2 Parasitic power is not included in the operational profiles presented below.
Full power operation
The profile illustrated in Figure A.1 represents standard lighting setups that utilize basic switching devices such as time switchers or photosensors, where luminaires consistently operate at full power during nighttime hours each day.
Key x daily course of operation (h) y lighting level (%)
Figure A.1 — Full power operational profile
Multi-power operation
The multi-power profile, such as the bi-power profile illustrated in Figure A.2, includes multiple time periods throughout the day when luminaires operate at varying power levels corresponding to different lighting intensities Each lighting level should be determined based on the appropriate lighting class.
Key x daily course of operation (h) y lighting level (%)
Figure A.2 — Bi-power operational profile
Operation with vehicle and presence detectors
When vehicle and presence detectors are utilized for lighting control, the operational profiles, whether full power or multi-power, are limited by periods of inactivity detected by the sensors, resulting in reduced lighting levels An example of a tri-power operational profile is illustrated in Figure A.3, which maintains a minimum lighting level throughout the night The peaks shown in the figure are dependent on sensor activity and are not periodic To calculate the Annual Energy Consumption Index (AECI), it is essential to assume an annual probability parameter for each lighting level.
Key x daily course of operation (h) y lighting level (%)
Figure A.3 — Tri-power detector-driven operational profile
Example of calculation
Calculation of the energy performance indicators PDI (Clause 4) and AECI (Clause 5) is additionally explained by means of an example depicted in Figure A.4
A generic road profile consists of two lane carriageway with sidewalks on both sides and grass strips separating them from carriageway
Lighting poles are strategically placed in the grass strip between the carriageway and the right sidewalk, featuring two luminaires per pole: Luminaire P R for illuminating the carriageway and the left sidewalk, and Luminaire P F, which enhances illumination on the right sidewalk The system power for both luminaires is based on the manufacturer's nominal specifications When assessing energy performance according to EN 13201-3, the power of P R and P F is considered only once for typical fields between consecutive poles However, for longer road sections, all associated luminaires are included in the calculations The illuminated areas for the carriageway, left sidewalk, and right sidewalk can be determined based on the road profile's widths and the installation length Illuminance levels for these areas must also comply with EN 13201-3, while grass strips and edge illuminance ratio areas are excluded from energy performance calculations.
To calculate the Annual Energy Consumption Index (AECI), it is essential to consider the lighting control profile of the system, which includes the reduction coefficient and the annual operation time for each operational regime, as well as the probability of motion detection if applicable For instance, in the commonly used bi-power operation, the total annual operation time is segmented into the full operation time (\$t_{\text{full}}\$) and the reduced lighting level time (\$t_{\text{red}}\$), where the system's power is decreased by the reduction coefficient (\$k_{\text{red}}\$).
Figure A.4 — Situation and description of parameters for calculation of PDI and AECI as an example
When applied to the situation in Figure A.4, and respecting the assumptions mentioned above, Formulae (1) and (3) for the calculation of energy performance indicators become as follows:
P R is the system power of the main luminaire in the lighting installation, in W;
P F is the system power of the auxiliary luminaire for illumination of the right sidewalk, in W;
A R is the area of the carriageway, in m 2 ;
A FL is the area of the left sidewalk, in m 2 ;
A FR is the area of the right sidewalk, in m 2 ;
E R is the calculated maintained illuminance on the road, in lx;
E FL is the calculated maintained illuminance on the left sidewalk, in lx;
E FR represents the maintained illuminance measured in lux (lx) on the right sidewalk The variable t full indicates the total annual operation time for full-level illumination, expressed in hours (h) Conversely, t red denotes the annual operation time for reduced-level illumination, also in hours (h) Additionally, k red is the coefficient that quantifies the reduction for the reduced level of illumination.
In Formula (A.2), for both luminaires the same lighting control profile is applied.
Typical values of energy performance indicators
General
The energy performance indicators, PDI and AECI, are influenced by various factors including lighting class, road profile, carriageway and sidewalk width, light source type, optics quality, and lamp positioning in luminaires Additionally, the switching and control profile can significantly impact AECI values When lighting systems are optimized for specific photometric parameters, energy performance can vary, with lower PDI and AECI values indicating better energy efficiency.
The energy performance indicators PDI and AECI provided in this annex are derived from extensive calculations of optimized lighting systems across various road profiles, lighting classes, light source types, and commonly used luminaires These values are not meant to serve as benchmarks; rather, they are designed to illustrate the absolute values of the indicators and their variations, helping to differentiate between more and less energy-efficient solutions.
Assumptions taken into for sample calculations are as follows:
— width of sidewalks and grass strips, where applicable, equals to 2 m;
— for road reflection properties the R3 table is considered;
— mounting height is optimized within the range 5 m to 12 m (step: whole numbers);
— spacing of lighting poles is optimized and sought between 20 m to 60 m (step: 1 m);
— arm overhang is ranged from 0 m to 2 m with the (step: 0,5 m);
— annual operation time 4 000 h at full power
The lighting system is typically arranged in a single-sided configuration, although an opposite arrangement may be used for wider carriageways Each calculation optimizes the geometry of the lighting system, prioritizing spacing to maximize the illuminated area while minimizing energy performance indicators The mounting height and arm length have an indirect impact on these indicators.
Luminaires for calculations include a range of options, from budget-friendly to advanced designs featuring reflecting diffusers or high-quality smooth and faceted reflectors The types of lamps utilized encompass ellipsoidal and tubular high-pressure sodium lamps, mercury lamps, metal halide lamps, and various wattages of LEDs When adjustable, the positioning of the lamp within the luminaire is optimized rather than left as a variable.
NOTE Calculations are based on lighting products (luminaires) available in Q1/2014.
Two-lane road for motorized traffic (road profile A)
Table A.1 — Typical values of the Power Density Indicator D P in mW.lx -1 m -2 for road profile A
Lighting class Width of carriageway m
Mercury Metal halide Sodium elliptical Sodium tubular LED
Table A.2 — Typical values of the Annual Energy Consumption Indicator D E in kWh.m -2 for road profile A
Lighting class Width of carriageway m
Mercury Metal halide Sodium elliptical Sodium tubular LED
Road with mixed motorized and pedestrian traffic without sidewalks (road profile B)
Table A.3 — Typical values of the Power Density Indicator D P in mW.lx -1 m -2 for road profile B
Lighting class Width of carriageway m
Mercury Metal halide Sodium elliptical Sodium tubular LED
Table A.4 — Typical values of the Annual Energy Consumption Indicator D E in kWh.m -2 for road profile B
Lighting class Width of carriageway m
Mercury Metal halide Sodium elliptical Sodium tubular LED
Road and sidewalk on the side of lighting arrangement (road profile C)
Table A.5 — Typical values of the Power Density Indicator D P in mW.lx -1 m -2 for road profile C
Lighting class Width of carriageway m
Mercury Metal halide Sodium elliptical Sodium tubular LED
Table A.6 — Typical values of the Annual Energy Consumption Indicator D E in kWh.m -2 for road profile C
Lighting class Width of carriageway m
Mercury Metal halide Sodium elliptical Sodium tubular LED
Road and sidewalk on the opposite side to the lighting arrangement (road profile D)
Table A.7 — Typical values of the Power Density Indicator D P in mW.lx -1 m -2 for road profile D
Lighting class Width of carriageway m
Mercury Metal halide Sodium elliptical Sodium tubular LED
Table A.8 — Typical values of the Annual Energy Consumption Indicator D E in kWh.m -2 for road profile D
Lighting class Width of carriageway m
Mercury Metal halide Sodium elliptical Sodium tubular LED
Road and two sidewalks on both sides (road profile E)
Table A.9 — Typical values of the Power Density Indicator D P in mW.lx -1 m -2 for road profile E
Lighting class Width of carriageway m
Mercury Metal halide Sodium elliptical Sodium tubular LED
Table A.10 — Typical values of the Annual Energy Consumption Indicator D E in kWh.m -2 for road profile E
Lighting class Width of carriageway m
Mercury Metal halide Sodium elliptical Sodium tubular LED
Road and two sidewalks on both sides separated from carriageway by grass strips (road profile F)
Table A.11 — Typical values of the Power Density Indicator D P in mW.lx -1 m -2 for road profile F
Lighting class Width of carriageway m
Mercury Metal halide Sodium elliptical Sodium tubular LED
Table A.12 — Typical values of the Annual Energy Consumption Indicator D E in kWh.m -2 for road profile F
Lighting class Width of carriageway m
Mercury Metal halide Sodium elliptical Sodium tubular LED
Typical values of AECI for different operational profiles
The typical values of AECI outlined in sections A.3.2 to A.3.7 are based on a full power operational profile, which assumes an annual operation time of 4,000 hours To account for varying operational profiles, it is generally effective to combine the annual operation times of different lighting levels with their corresponding system power and detection probability in systems equipped with detectors This results in a single lighting operation coefficient, denoted as \( c_{op} \), which can be used to adjust the AECI for full power operation, providing the AECI value for the actual operational profile.
Table A.13 shows typical values of the lighting operation coefficient c op for different operational profiles under these assumptions:
— Full power: 4 000 h operation at full power P;
— Bi-power: 2 175 h at full power P and 1 825 h at reduced power 0,7⋅P with lighting level reduced to
— Tri-power: 2 175 h of bi-level lighting control between 100 % and 60 % of the system power with detection probability of 80 % and 1 825 h of reduced bi-level lighting control between 20 % and
60 % of system power with detection probability of 20 %
Table A.13 — Typical values of the lighting operation coefficient c op in % for different operational profiles
General
Installation luminous efficacy is calculated with the following formula: inst L M LO ls P η =C f U R⋅ ⋅ ⋅ ⋅η η⋅ (B.1) where η inst is the installation luminous efficacy in lm.W -1 ;
C L is the correction factor for luminance or hemispherical illuminance based lighting designs; f M is the overall maintenance factor (MF) of the lighting installation;
U is the utilance of the lighting installation;
R LO represents the optical efficiency of luminaires in a lighting installation, while η ls denotes the luminous efficacy of the light sources utilized, measured in lm.W\(^{-1}\) Additionally, η P indicates the power efficiency of the luminaires employed in the installation.
The installation luminous efficacy η inst should be evaluated considering the real operating conditions of the lighting installation
Maintenance factor should be the same as used for the calculation of photometric parameters according to EN 13201-3.
Calculation of the correction factor
When the minimum requirement for road surface luminance is specified, the effectiveness of the lighting installation can vary significantly This variation may arise from the average luminance coefficient of the road surface, denoted as \$Q_0\$, deviating from the standard value of \$0.07 \, \text{cd} \cdot \text{m}^{-2} \cdot \text{lx}^{-1}\$, or due to the specific directionality of the illumination To account for these factors, a correction factor is calculated using a specific formula.
E i,min is the minimum required average illuminance;
The sub-area, denoted as \$A_i\$, is where the minimum average illuminance must be met, while \$\Phi_A\$ represents the luminous flux that illuminates this area Additionally, \$n\$ indicates the total number of sub-areas that require lighting.
For an area A i where the lighting design criterion is the minimum road surface luminance L i,min , the value of the minimum required average illuminance is set to:
For an area A i where the lighting design criterion is the hemispherical illuminance E hs, the value of the minimum required average illuminance is set to: hs / 0,65
NOTE The value 0,65 is empirical and represents an average value for variety of lighting installations.
Calculation of the utilance
Utilance (U) is defined as the ratio of the luminous flux received by the reference surface to the sum of the individual total fluxes of the luminaires of the installation:
U ⋅Φ ⋅ n R (B.5) where Φ A is the luminous flux reaching the area to be illuminated, in lm; Φ ls is the luminous flux emitted from the light source(s) in a luminaire, in lm;
R LO is the optical efficiency of luminaires used in the lighting installation; n lu is the number of luminaires of the installation.
Calculation of the efficiency of luminaires
The luminous efficacy of a luminaire is typically lower than that of the lamp(s) it contains, primarily due to optical losses and the energy consumed by the control gear The optical efficiency, often referred to as the Light Output Ratio (LOR), represents the ratio of luminous flux emitted by a luminaire to the luminous flux produced by its internal lamp(s) This ratio can be determined using photometric data and is generally provided by luminaire manufacturers.
Power efficiency of a luminaire is the ratio between power of lamp(s) and the system power of the luminaire:
P ls is the power of lamp(s) inside the luminaire, in W;
P is the system power of the luminaire, in W
NOTE 1 For some LED based luminaires values for P ls , η ls and R LO are not available and need to be replaced by the overall luminaire’s luminous efficacy
NOTE 2 In general, the system power P can include also other devices which are outside luminaires but directly associated with the area to be illuminated
Lighting factor of an installation
Installation lighting factor q inst
EN 13201-2 mandates that lighting systems for motorized roads must be designed based on average road luminance levels, categorized under M lighting classes Additionally, the power density indicator (D P), system power (P), and annual energy consumption indicator (D E) are influenced by the average horizontal illuminance (E).
In M lighting classes, lighting designers must choose luminaires that achieve the road luminance \( L \) as specified in EN 13201-2 while minimizing road illuminance \( E \) To facilitate a straightforward comparison of energy performance across various luminaires and installations, it is crucial to utilize a simple parameter This can be effectively accomplished using the installation luminance factor \( q_{inst} \).
L is the calculated average maintained road luminance in accordance with EN 13201-3:2015, 7.1 and 8.2, in cd.m -2 ;
E is the calculated average maintained horizontal illuminance of the road surface when the road surface luminance is L , in lx;
Q 0 is the average luminance coefficient of the r-table adopted in luminance calculation, in sr -1
NOTE It is a normalizing parameter, which gives q inst a dimensionless character through reference to a standardized photometric property of the road surface.
Role of q inst in road lighting design aimed at energy saving
The proposed factor \$q_{inst}\$ aligns with CIE 144 recommendations, emphasizing the importance of the luminance to illuminance ratio in road lighting Typically ranging from 0.8 to 1.3, \$q_{inst}\$ is closely linked to energy consumption and environmental sustainability Notably, higher values of \$q_{inst}\$ within this range can lead to a significant 40% reduction in the power density indicator \$D_P\$, highlighting its importance in energy-efficient lighting solutions.
The factor \$q_{inst}\$ characterizes the energy performance of road lighting installations, allowing for assessment regardless of the specific lighting components used Road luminance and illuminance can be derived from lighting design or direct measurements, enabling evaluations even without knowledge of the light sources or luminaires This factor facilitates immediate evaluation of energy consumption performances during the design stage, eliminating the need for additional calculations Furthermore, \$q_{inst}\$ allows for straightforward comparisons of efficiency between various installation types, especially when contrasting older systems with modern solutions.
Typical values of q inst
Experience shows that good results for energy consumptions and environmental compatibility can be obtained with q
Presentation of energy performance indicators
The power density indicator (PDI) and annual energy consumption indicator (AECI) are essential compound parameters that should always be presented together It is crucial to clearly display all values and assumptions used in the calculation of these energy performance indicators An example can be found in Table D.1 Additionally, graphical representations of the operational profile may serve as an effective presentation method in certain cases.
Table D.1 — Example of information to be presented together with energy performance indicators System power
Luminaire 1 Luminaire 2 Luminaire 3 Luminaire 4 Luminaire 5
Sub-area 1 Sub-area 2 Sub-area 3 Sub-area 4 Sub-area 5
Period 1 Period 2 Period 3 Period 4 Period 5
Period 1 Period 2 Period 3 Period 4 Period 5
Annual energy consumption indicator D E (Wh.m -2 )
NOTE The table can be extended by additional luminaires, sub-areas or time periods if needed
[1] CEN/TR 13201-1, Road lighting — Part 1: Guidelines on selection of lighting classes
[2] EN 13201-4, Road lighting — Part 4: Methods of measuring lighting performance
[3] CIE S 017/E: 2011, ILV, International Lighting Vocabulary
[4] CIE 115:2010, Lighting of Roads for Motor and Pedestrian Traffic
[5] CIE 144:2001, Road Surface and Road Marking Reflection Characteristics
[6] CIE 154:2003, The Maintenance of Outdoor Lighting Systems