Outdoor lighting calculation: what it depends on, methods and what is needed for it

What a calculation answers and what it consists of

A lighting calculation answers one question: are the required levels present on the calculation surface, and with what margin. The result is a pole layout, the type and power of luminaires and a table of values at calculation points. Without it, pole height, bracket reach and the number of luminaires per pole are chosen by eye.

The order is always the same: the standard for the object, the geometry (plan, widths, heights), the luminaire’s photometry and the maintenance margin, and only then the numbers. The required levels for streets, courtyards, sites and car parks are collected in the article on required illuminance levels.

For a pole manufacturer the calculation is also a source of data: it gives the height of the light centre, the bracket reach and tilt, and the number and mass of luminaires on each pole. The shaft section and the foundation depend on these, as covered in the article on lighting pole design.

Input data

A calculation is no better than its input. Below is what is needed and why each line affects the result.

What is in a photometric file

A .ldt or .ies file is a table of the luminaire’s luminous intensity in candelas by direction: angles around the luminaire and from the vertical. Alongside are the rating data: flux, power, dimensions. The formats differ but the substance is the same, and which one to use depends on what the calculation software reads.

The file must belong to exactly the variant that is being bought. Luminaires of one type come in versions with different optics and power, and a calculation from someone else’s file is worth nothing.

DBN defines luminaire efficiency as the ratio of the luminaire’s total flux to the sum of the fluxes of its sources measured outside it (cl. 3.24). The data sheet of an LED luminaire usually already gives the luminaire’s flux, and multiplying it by the efficiency again is wrong. If the calculation starts from the flux of the modules, the efficiency is a multiplier. This is the typical place where flux is counted twice or not at all.

What is calculated

Different objects are specified by different quantities. The table shows what each quantity is and where its standard is.

Horizontal and vertical illuminance: which is needed where

Horizontal illuminance answers how much light lands on the ground. Vertical shows how much falls on a standing or walking person, a window or a facade. For a pavement the first is usually enough. For a crossing, an entrance, a market and the aisles between rows both are needed.

On open markets DBN sets a direct condition: the ratio of vertical to horizontal illuminance must be at least 1:2, with the vertical measured in a plane across the aisle axis at 1.5 m height and the horizontal at surface level (cl. 8.5.28). At crossings the vertical component is obtained with the optics, as covered in the article on pedestrian crossing lighting.

Vertical illuminance is also limited on the neighbours’ side. On streets of categories A and B, lighting of all kinds must not create on the windows of dwellings more than 7 lx where the carriageway luminance is 0.4 cd/m², 10 lx for 0.6–1.0 cd/m² and 20 lx for 1.2–2.0 cd/m²; on windows of hospital wards and sleeping blocks not more than 5 lx (cl. 8.5.37).

Luminance instead of illuminance

On asphalt concrete and surfaces treated with bituminous binder the carriageway is specified by luminance, and on setts, cement concrete and slabs by illuminance (note 1 to table 8.27). Luminance depends on how the surface reflects light towards the driver, so it is not calculated by hand: the reflection properties of the surface are needed for every pair of directions, and DBN names both reflection and diffusion in the definition in cl. 3.72.

In practice this means that a carriageway with asphalt concrete needs software and data on the surface. The performance parameters of road lighting are given in the DSTU EN 13201 series, which the DBN bibliography cites after Amendment No. 1. We do not copy its numbers here.

Three calculation methods

The methods differ in what they calculate and in how much detail. The first is enough for a draft layout, the second is needed to check the minimum and vertical illuminance, and the third is almost always used when submitting a project for a street or a road.

Utilization factor

The method starts from the flux: what part of it lands on the calculation strip and over what area it is spread. Average maintained illuminance is:

Eavg = Φ · UF / (Km · w · s)

Here Φ is the luminaire flux (the sum, if a pole carries several luminaires), UF is the utilization factor, the share of flux that lands on the strip, Km is the maintenance factor, w is the strip width and s is the pole spacing along the strip. UF is read from the table in the luminaire’s photometric data for the required geometry (strip width, height, position relative to the edge). In a staggered layout the spacing along the street is half the spacing on one side; in an opposite layout two poles stand in a cross-section, so the flux in the numerator is doubled.

It also works in reverse: the same formula gives the largest spacing at which average illuminance is still not below the standard, or the required luminaire flux for a given spacing. It is the first estimate before the point calculation.

Point method

The method takes the luminous intensity from the luminaire file in the direction of the point and divides it by the square of the distance. For a horizontal surface and one point it looks like this:

Eh = Σ I(γ) · cos³γ / h²

I(γ) is the intensity in the direction of the point, γ is the angle between the vertical and that direction, h is the height of the light centre above the calculation plane; the contributions of all luminaires lighting the point are added. For a vertical surface turned towards the luminaire, sin γ · cos²γ stands in place of cos³γ.

A point is used to check the worst places. On a straight stretch these are the edge of the strip midway between two poles (the minimum) and the spot under a pole (the maximum). The method does not replace a grid, but it lets you check the software result by hand at a few points, and such a spot check is not superfluous.

Calculation in software

In the software, poles and luminaires from photometric files are placed on the plan, and the calculation surface with its grid of points, the surface type and the maintenance factor are set. It gives values at every point, isolines, Eavg, Emin, uniformity and, for roads, luminance and TI. This is the table that goes into the project.

The software treats as correct whatever was typed in. So the engineer’s responsibility is that the layout matches the drawings, the file matches the luminaire being bought, and the maintenance factor and tilt are written out. What is checked at review is in a separate section below.

Maintenance factor and loss of luminous flux

A new luminaire is brighter than it is five years later. DBN defines the maintenance factor Km as a design factor that accounts for the fall in illuminance in service due to dirt and ageing of light sources and luminaires (cl. 3.21). In outdoor lighting projects it must be taken into account (cl. 8.5.9). For LED luminaires it is calculated under appendix V, and the ingress protection must be at least IP53, on condition of cleaning twice a year.

The principle is that the calculation is made for the end of the maintenance period. Initial illuminance is Km times higher than the standard, and the standard is compared with the maintained value. Appendix V links Km to the maintenance factor MF:

Km = 1 / MF, MF = LLMF · LSF · LMF · RSMF

The designation L80 B10 – 50 000 h, per note 2 to table V.4, means that after 50 thousand hours the flux of the LED modules or the luminaire will be at least 80 % of the initial value, and B10 that 10 % of modules may have a flux below that limit.

How it is used and where the trap is

Appendix V is based on an international guide to the maintenance of indoor lighting systems, so tables V.5–V.8 were compiled for rooms. Outdoors the factor RSMF is taken as one, while the cleanliness class and the cleaning interval are chosen by the designer and written into the calculation. If the luminaire maker gives its own LLMF and LMF values, they are compared with the appendix, not substituted silently.

A typical mistake is to take Km = 1.0 «for simplicity». Then the standard is met on paper and a few years later not on the ground. A second mistake is not stating in the project the cleaning interval the calculation relied on: the operator does not know about it and cleans less often.

Other values found in the standards are covered in the article on required illuminance levels: a maintenance factor of 0.67 for industrial territories (cl. 8.3.7), and for sports installations with television coverage the maintenance factor set in DBN V.2.2-13.

Separately, on lowering the level at night. The dimming mode is calculated as a separate mode. On park roads, pedestrian and cycle paths, car parks and drive-ways it is not applied (cl. 8.5.59). DBN does not allow switching off part of the luminaires at night at all in a single-row layout with one luminaire per pole (cl. 8.5.11).

Layouts, height and spacing

There are four layouts: one-sided, two-sided staggered, two-sided opposite (poles facing each other) and central (on the median). The practical ratios of strip width, height and spacing are covered in the articles on pole height and distance between poles. Here we cover what the calculation shows about them.

Height and spacing pull the result in different directions. Illuminance under a luminaire falls roughly as 1/h² (see the point-method formula), so raising the luminaire loses level under it but gives a longer and wider spot. A smaller spacing raises the minimum between poles and increases the number of poles and luminaires. The calculation finds the point where the minimum and uniformity still pass with no more poles than needed: DBN names as the optimization criterion the minimum power of the installation while meeting the specified indicators (cl. 8.5.17).

What else DBN requires of the layout

• luminaires are placed so that the line they form clearly shows the direction of the road (cl. 8.5.10);
• placement takes account of convenient access for installation and maintenance (cl. 8.5.18);
• growth of greenery: provision is made so that crowns do not screen the luminous flux (cl. 8.5.38);
• lower height limit set by glare: for luminaires with a cut-off angle below 15° by table 8.9, and on category B streets and in installations specified by horizontal and semi-cylindrical illuminance this table is named directly in cl. 8.5.60;
• minimum height above the carriageway, pedestrian paths and squares under PUE is in the article on street and road lighting standards.

Example: a pedestrian approach to a building in a courtyard

The example is small and deliberately done by hand, so that the mechanics are visible. The luminaire is a model: real luminous intensity comes from its file, not from an assumption.

Step 1. Maintenance

We take 50 000 h of running time. From table V.4 for L80 B10 – 50 000 h: LLMF = 0.85, LSF = 1. From table V.5 for type E (IP5X), cleaning every six months (that is how the condition of cl. 8.5.9 reads) and cleanliness class N: LMF = 0.93. RSMF is taken as 1. Then MF = 0.85 × 1 × 0.93 × 1 = 0.79 (more exactly 0.7905), and Km = 1 / 0.79 = 1.27.

So the initial average illuminance must be at least 4 × 1.27 = 5.08 lx. Cleanliness class N is defined in DBN for rooms, so this is the designer’s assumption, and it must be written in the calculation explicitly.

Step 2. Upper limit of spacing by average illuminance

Luminous intensity of the model: I = Φ / (2π (1 − cos 75°)) = 2000 / (6.283 × 0.741) ≈ 429 cd. The share of flux falling on the strip 0–4 m from the pole line is, for this model, UF = 0.278, that is 556 lm out of 2000. From the reverse form of the formula: s ≤ Φ · UF / (w · Einit) = 556 / (4 × 5.08) ≈ 27.4 m.

This is an upper limit by average illuminance only. Whether uniformity holds is shown by the next step.

Step 3. Point method for a spacing of 25 m

We take a spacing of 25 m, that is 5 mounting heights. For each point Eh = I · cos γ / r², where r² = d² + h² and d is the horizontal distance to the luminaire.

• under the luminaire (edge of the strip): cos γ = 1, E = I / h² = 429 / 25 ≈ 17.2 lx; the neighbouring poles at 25 m give tan γ = 25 / 5 = 5, that is γ = 78.7°, which is outside the cone, so their contribution is zero;
• far edge of the strip midway between poles: r² = 12.5² + 4² + 5² = 197.25, cos γ = 5 / 14.05 = 0.356, E = 429 × 0.356 / 197.25 ≈ 0.775 lx from each of the two neighbouring poles, 1.55 lx together;
• average illuminance: 556 / (4 × 25) = 5.56 lx; a grid of points calculated by the point method gives the same, so the two methods agree.

At a spacing of 27 m Emin / Eavg = 0.25, at 28 m already 0.237. So uniformity limits the spacing practically at the same place as average illuminance, and a spacing of 25 m leaves a margin.

What the example does not check

A spacing of 25 m comes to 5 mounting heights, more than the practical ratio in the article on distance between poles. This is a consequence of a model with an abrupt cut-off of light outside the cone. A real luminaire with a softer curve will give a different picture, so the rule in the article remains a guide, and the answer comes from the file.

Not considered: glare to the pedestrian from intensity at high angles, vertical illuminance, the end sections of the strip, a bend in the path, trees and the effect of the bracket. A luminaire with a cut-off angle below 15° at a height of 5 m would not pass table 8.9 (semi-wide distribution, flux up to 6000 lm requires 7.0 m). In the model the angle is exactly 15°, so this check is waived, but in a real calculation the cut-off angle is read from the data sheet. Dimming does not apply to a pedestrian path (cl. 8.5.59).

What is checked when reviewing a calculation

Reviewing a calculation is not recalculating it but going through the places where it most often breaks. The first items are the cheapest to check.

• the table and class used are named, not just «per DBN»; for crossings, entrances and car parks their own standards are applied (see the articles on crossings and required levels);
• the specified quantity matches the surface: luminance on asphalt concrete, illuminance on setts, slabs and cement concrete;
• the calculation surface matches the plan, and the grid of points is dense enough not to miss the minimum midway between poles and near the edges;
• pole positions in the calculation match the plan and the schedule of poles. They most often differ like this: the calculation was done at an ideal spacing, and on the plan a pole was moved because of utilities or an entrance;
• height, reach and bracket tilt in the calculation are the same as in the pole drawing;
• the photometric file belongs to the variant being bought, and the flux is not counted twice through the efficiency;
• Km is not equal to one, its components and the cleaning interval are written down; maintained values are not mixed up with initial ones;
• the average, the minimum and the uniformity are checked together: the average is often met thanks to a bright spot under the pole while it stays dark between poles;
• glare: cut-off angle and height under table 8.9, TI and intensity at high angles on roads;
• vertical illuminance at the windows of neighbouring buildings and light pollution where a standard exists for them;
• trees: the layout is checked against the crowns in a few years;
• the dimming mode was calculated separately, and where it is prohibited it was not assumed.

What is issued as the result

The result of a calculation is not one number but a package a pole manufacturer and installers can work from.

• a layout plan: pole positions, height of the light centre, reach, tilt and orientation of luminaires;
• a schedule of luminaires: type, variant, power, flux, optics, number per pole. It passes into the schedule of poles and masts, as covered in the article on the set of lighting working drawings;
• tables of values at grid points or isolines: Eavg, Emin, Emax, uniformity, for roads also luminance and TI;
• the maintenance factor with its components and the cleaning interval;
• a compliance table: indicator, requirement, result, clause of the standard;
• mass and wind area of the luminaires at each position. The pole structure is calculated from these, not from the lighting calculation itself.

What to send us for a calculation

We carry out the lighting calculation to the standards ourselves, and on request we fit poles with luminaires for streets and courtyards and masts with floodlights. For the calculation we need a plan with possible pole positions, the illuminance level or class (street category, competition class), the city and the name of the object. If there is no plan yet, a sketch with dimensions is enough.

If the client has their own requirements or has already chosen luminaires, name them. In reply we send the layout, the number and power of luminaires, a table of illuminance levels and the uniformity. Installation is carried out by a partner construction company.

A rough pole estimate before the calculation can be made in the lighting pole selection calculator. The city is also needed for wind loading: see the wind regions of Ukraine. On choosing a floodlight mast see the article Which floodlight mast to choose, for the general list for a request How to order poles and masts, and for the service itself the lighting calculation page.

Standards and validity

DBN V.2.5-28:2018 «Natural and artificial lighting». In the e-construction.gov.ua register its status is «In force»; approved by Ministry of Regional Development order of 03.10.2018 No. 264. Amendment No. 1 was approved by Ministry of Development order of 13.08.2025 No. 1254 and has applied since 01.01.2026. The clauses, formulas and tables of this article are taken from the updated text with Amendment No. 1 as of 25 October 2026 (section 3, cl. 8.3.4, 8.5.x, tables 8.9, 8.27–8.33, appendices V and L).

DBN B.2.2-5:2011 «Improvement of territories»: cl. 4.10 refers the outdoor lighting of settlements to DBN V.2.5-28 and DBN V.2.3-5. The DSTU EN 13201 series (parts 1–5, adopted as national standards in 2016) is named in the bibliography of DBN V.2.5-28 after Amendment No. 1; its numbers are not reproduced here, and which edition of the standard the client or the expert review accepts is checked before it is cited in a project.

The numbers of the example (flux, intensity of the model, UF) are assumed and serve only to show the arithmetic; the values of the standards in it are taken from the clauses listed. For a project, the current edition of the standards and the design brief are used.