- EN 13201 is divided into five parts. Part 2 defines classes and quantitative requirements. Part 3 defines the calculation method (the basis for DIALux). Part 5 covers energy performance.
- ME classes (Motorway Equivalent) use luminance measurement (cd/m²) and apply to carriageways. ME3a is the most common class on Swedish municipal roads; ME6 applies to the lowest-classified routes.
- S classes use horizontal illuminance (lux) and apply to footpaths, cycle paths, car parks, and border zones.
- Writing “150 lux” in a tender document is not a class requirement — it is a point value with no connection to uniformity, glare, or road surface reflectance. Specify ME class instead.
The Five Parts of the Standard
EN 13201 Road lighting (adopted as SS-EN 13201 in Sweden) was published in its current version in 2015 and complements national guidelines from the Swedish Transport Administration (Trafikverket) and individual municipalities for how road lighting should be selected, calculated, and evaluated.
| Part | Title (abr.) | Content |
|---|---|---|
| Part 1 | Selection of lighting classes | How road type, traffic, and environment determine which class applies. Decision matrices and influencing parameters. |
| Part 2 | Performance requirements | Numerical minimum requirements per class: Lm, Uo, Ul, TI, SR. The part cited in procurement documents. |
| Part 3 | Calculation method | Exactly how luminance and illuminance are calculated with the numerical point-grid method. The basis for DIALux, Relux, and DIALux Evo. |
| Part 4 | Measurement method | Field measurements of completed installations. Which points to measure, at what operating hours, and under what weather conditions. |
| Part 5 | Energy performance | AECI (Annual Energy Consumption Indicator) and the DE indicator. Enables comparison of energy use between road lighting installations per luminance unit. |
ME Classes — Carriageways and Luminance
ME classes (M = “Motorway/main road Equivalent”) use luminance as the primary criterion — not illuminance in lux. The rationale is that the eye on a road at night perceives luminance (the reflected light from the road surface), not incident light directly.
ME classes apply to carriageways in segments where vehicles move at relatively higher speeds. A complete DIALux model for an ME class requires:
- Road surface reflectance table (R-table, e.g. R3 for smooth asphalt)
- Observer position (60 m ahead of luminaire, 1.5 m height)
- Calculation point grid per Part 3
Below are the core ME classes and their minimum requirements per Part 2:
| Class | Lm (cd/m²) | Uo (≥) | Ul (≥) | TI (≤%) | SR (≥) |
|---|---|---|---|---|---|
| ME1 | 2.0 | 0.40 | 0.70 | 10 | 0.50 |
| ME2 | 1.5 | 0.40 | 0.70 | 10 | 0.50 |
| ME3a | 1.0 | 0.40 | 0.70 | 15 | 0.50 |
| ME3b | 1.0 | 0.40 | 0.60 | 15 | 0.50 |
| ME3c | 1.0 | 0.40 | 0.50 | 15 | 0.50 |
| ME4a | 0.75 | 0.40 | 0.60 | 15 | 0.50 |
| ME4b | 0.75 | 0.40 | 0.50 | 15 | 0.50 |
| ME5 | 0.50 | 0.35 | 0.40 | 15 | 0.35 |
| ME6 | 0.30 | 0.35 | — | 15 | — |
Lm = maintained average luminance. Uo = overall uniformity (min/average). Ul = longitudinal uniformity (min in lane/max in lane). TI = threshold increment (disability glare). SR = surround ratio. All values per EN 13201-2:2015, Table 1.
The Parameters Explained
S Classes and CE Classes
S classes (S1–S7) apply to street areas without high-speed through traffic: footpaths, cycle paths, residential streets, and car parks. Here horizontal illuminance (lux) is used instead of luminance, because there is no unified moving observer.
| Class | Em (lux, ≥) | Emin (lux, ≥) |
|---|---|---|
| S1 | 15 | 5 |
| S2 | 10 | 3 |
| S3 | 7.5 | 1.5 |
| S4 | 5 | 1 |
| S5 | 3 | 0.6 |
| S6 | 2 | 0.6 |
| S7 | 2 | — |
Em = maintained average horizontal illuminance; Emin = maintained minimum horizontal illuminance. Per EN 13201-2:2015, Table 3.
CE classes (CE0–CE5) apply to conflict areas with complex traffic: intersections, roundabouts, pedestrian crossings, and complex traffic environments. CE uses horizontal illuminance (like S) but with higher level requirements adapted to the increased accident risk.
The Maintenance Factor (MF) — One of the Most Important Variables
The calculation programme (e.g. DIALux) calculates newly installed light output and then applies a maintenance factor (MF) to simulate the system's condition at the end of the maintenance interval. The formula is:
MF = LLMF × LSF × LMF × RSMF
- LLMF (Lamp Lumen Maintenance Factor) — LED lumen depreciation over time. Typically 0.85–0.95 at 50,000 h for LED.
- LSF (Lamp Survival Factor) — proportion of functioning units at end of interval. Almost always 1.0 for LED within reasonable maintenance intervals.
- LMF (Luminaire Maintenance Factor) — dirt depreciation on glass/optics. Typically 0.90–0.95 for IP66 luminaire in road environment at 3–5 years.
- RSMF (Road Surface Maintenance Factor) — change in road surface reflectance. Often 1.0 when R-table is known.
A typical MF for a modern LED luminaire with IP66 in road lighting is 0.80–0.85 at a 4-year maintenance interval. This means the luminaire's newly installed output must be ~18–25 % higher than the numerical class value to meet the Lm requirement at end of interval. This is directly related to the discussion of real versus modelled performance in DIALux does not calculate everything.
How to Choose the Right Class
Part 1 of EN 13201 sets out a decision process based on:
- Traffic flow and speed — higher gives higher class (ME1–ME2 for motorways, ME4–ME6 for low-traffic municipal roads)
- Presence of pedestrians and cyclists — raises SR requirement and influences CE selection
- Environmental complexity — intersections, parking, urban areas require higher class than straight through-routes
- Ambient luminance — in stretches with high ambient luminance (retail district) a lower ME class may be acceptable
ME3a–ME3c are the most common classes on European municipal roads with mixed traffic.
Energy Performance — Part 5 and AECI
EN 13201-5 introduces an energy performance metric: AECI (Annual Energy Consumption Indicator) in kWh/(m²·year), calculated per illuminated road surface. This enables comparison of energy use between installations serving equal road lengths but with different luminaire spacings and power levels.
AECI is not yet mandatory in most municipal procurement, but including an AECI requirement in tender documents gives the municipality an objective energy comparison tool that goes beyond “watts per luminaire”.
Why “lux” in a tender document is not enough
“Minimum 15 lux on carriageway” is simple to write in a specification — but says nothing about uniformity, disability glare (TI), surround ratio (SR), or how the value relates to the road surface reflectance. A luminaire can achieve 15 lux average with extreme non-uniformity and still fall outside the ME class requirements for Uo and Ul. ME class plus R-table are the correct parameters. For footpaths and cycle paths: S class with Em and Emin.
Five Points for Procurement
- Specify ME class, not just lux. For carriageways: state the class (e.g. ME3a) plus R-table (e.g. R3) and maintenance interval (e.g. 4 years) so that the calculated MF can be verified.
- Require a calculation file in DIALux or Relux. Without a complete .dlx/.rdf file with correct observer position, R-table, and MF it is difficult to verify that class values are actually met.
- Add SR verification. The surround ratio SR is often overlooked. For roads with pedestrian traffic, SR ≥ 0.5 should be a contract condition.
- Define field measurement. Specify that a Part 4 measurement is conducted no later than 12 months after commissioning. Define which party bears the cost if measured results do not meet the class.
- Request AECI. Include AECI (kWh/m²·year) per Part 5 as a comparison criterion, particularly in LCC (life-cycle cost) procurements.
VALDUR — Technical Note
The VALDUR luminaire's IES Type III/IV optics have been verified against ME3a and ME4a in representative DIALux scenarios with R3 table and MF = 0.82. Ready-made lighting calculations for specific road geometry and pole spacing are provided by POLAB. D4i Part 253 delivers real-time CLO so the installation maintains Lm throughout the maintenance interval without over-installation. More on how calculations are set up: DIALux does not calculate everything.
Related Articles
DIALux Does Not Calculate Everything
What the gap between model and reality means for EN 13201 class compliance
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Why photopic luminance does not give a complete picture of visual performance
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How IES type and CEN M-class drive lens selection
DALI-2, Zhaga, and D4i
CLO via D4i Part 253 maintains Lm throughout the maintenance interval
Sources
- CEN / BSI. (2015). EN 13201-1:2015 Road Lighting — Part 1: Guidelines on selection of lighting classes.
- CEN / BSI. (2015). EN 13201-2:2015 Road Lighting — Part 2: Performance requirements. (Source for all class values in this article.)
- CEN / BSI. (2015). EN 13201-3:2015 Road Lighting — Part 3: Calculation of performance.
- CEN / BSI. (2015). EN 13201-4:2015 Road Lighting — Part 4: Methods of measuring lighting performance.
- CEN / BSI. (2015). EN 13201-5:2015 Road Lighting — Part 5: Energy performance indicators.
- van Bommel, W. (2015). Road Lighting: Fundamentals, Technology and Application. Springer. (Reference for maintenance factor methodology and observer model.)