What a lighting study is
A lighting study is a calculation. It takes a room and a proposed set of luminaires and computes how much light each part of the room will receive, how evenly, and with how much glare. Each result is then compared with the requirement for the activity in that part of the room, so a study ends in a pass or a fail per zone, not in an impression.
What goes in
- The room: its dimensions, ceiling height and the reflectance of ceiling, walls and floor.
- The zones: where each task or activity takes place and which activity it is — the requirement belongs to the activity, not to the room.
- The luminaires: the product, its position and mounting height, and its photometric file, the measured light distribution the calculation runs on.
- The maintenance factor: how much of the new installation’s output you still count on at the end of its life.
What comes out
Per zone, the maintained illuminance, the uniformity and the glare rating, each set against the limit for that activity; under the 2021 edition of EN 12464-1 also the cylindrical, wall and ceiling illuminance. Around the numbers sit the drawings that make them readable — isolux lines or a heat map across the plan — and a luminaire list. A Momik study returns illuminance, uniformity, UGR and isolux per zone, in a PDF report with heat maps, a luminaire list and results zone by zone.
Who asks for one
Usually the project: a tender, a specification or a contract that calls up EN 12464-1. A standard is not law on its own — NBN, the Belgian standards body, calls standards voluntary — but a contract or set of specifications that refers to it makes it binding. For Belgian workplaces the law points to it as well: under the Code on well-being at work (art. III.1-32), an employer who applies NBN EN 12464-1 is presumed to meet the legal lighting duty; one who does not must at least meet the minimums in annex III.1-2. The study itself is made by whoever designs or supplies the lighting: a lighting designer or engineering firm, an installer, or a luminaire supplier as part of a quote.
Inputs to a lighting design: IBE-BIV, Guide pratique de l’éclairage des lieux de travail intérieurs, November 2023, chapter 12 — https://ibe-biv.be/wp-content/uploads/2023/11/IBE-BIV-NBN-EN-12464-1-2021-Guide-pratique-de-leclairage-des-lieux-de-travail-interieurs-adjust.pdf — legal status of standards: NBN FAQ, https://www.nbn.be/en/faq — the Belgian Code on well-being at work, art. III.1-32, as quoted in the same IBE-BIV guide, pages 5-6.
Glossary: the terms a lighting study uses
Eighteen terms, from the physics of light to the files and drawings in a report. The definitions follow the CIE International Lighting Vocabulary, which the CIE publishes free to read as the e-ILV; where EN 12464-1 adds a rule, the source is named in the note at the end.
Luminous flux — Φ, in lumen (lm)
The total light a source gives off, weighted for how sensitive the human eye is to each wavelength. It says how much light comes out, not where it goes.
Luminous intensity — I, in candela (cd)
How much of that flux leaves in one particular direction, per unit of solid angle. A luminaire’s intensity in every direction together is its light distribution — the data a photometric file carries.
Illuminance — E, in lux (lx)
The light arriving on a surface, per square metre: one lux is one lumen per square metre. Most lighting requirements are written in it — the task values in EN 12464-1 are illuminances.
Luminance — L, in candela per square metre (cd/m²)
Illuminance is light arriving at a surface; luminance is light leaving a surface in a given direction, per unit of projected area — the area as seen from that direction. Glare is calculated from it: the UGR formula uses the mean luminance of each luminaire’s light-emitting surface in the direction of the observer’s eye.
Luminous efficacy — η, in lumen per watt (lm/W)
Luminous flux divided by the electrical power consumed: how much light each watt buys. Two figures only compare fairly when both say whether the power of auxiliary equipment, such as a ballast, is counted.
Reflectance — ρ, a ratio (often written as a percentage)
The share of incoming light a surface reflects. Ceiling, wall and floor reflectance decide how much light bounces back into the room, so they are inputs to every calculation. The single UGR value on a luminaire datasheet assumes 70 % ceiling, 50 % wall and 20 % floor reflectance; in a real room the UGR can come out higher or lower.
Correlated colour temperature — CCT, in kelvin (K)
How warm or cool a white light looks, expressed as the temperature of the ideal (Planckian) radiator whose colour is nearest to it. Lower is warmer. EN 12464-1 sets no limit value for it; the Belgian guide to the standard calls sources below 3300 K warm, above 5300 K cool, and those in between neutral.
Colour rendering index — Ra
How faithfully a light source shows the colours of objects compared with a reference source, taken as the mean score over eight standard test colours. The Belgian guide to EN 12464-1 puts the floor at Ra 80 for most workplaces and Ra 90 where the work has special requirements.
Maintained illuminance — Ēm, in lux
The value below which the average illuminance on a surface is not allowed to fall — the CIE calls it maintained average illuminance. In EN 12464-1 every illuminance target is a maintained value: it must be met throughout the installation’s life — including just before scheduled maintenance, when the light sources have aged and dirt has built up.
Maintenance factor — MF, a ratio
What the installation delivers after a set time, divided by what it delivers when new. It links the two numbers: a new installation has to reach the maintained value divided by MF, so with an MF of 0.8 a 500 lx requirement means 625 lx on day one. The Belgian guide builds it from four parts — lumen maintenance of the light sources, their survival rate, luminaire soiling and room-surface ageing — following ISO/CIE TS 22012.
Uniformity — Uo, a ratio
The lowest illuminance on a surface divided by the average on it, so a zone cannot pass by being bright on average and dark in one corner. EN 12464-1 sets it per zone: at least 0.40 in the immediate surrounding area and 0.10 on the background; the task value is set per activity — 0.40 for filing and copying, 0.60 for writing, typing and reading in an office.
Unified Glare Rating — UGR; the limit is RUGL
The CIE method (CIE 117:1995) for rating discomfort glare — glare that bothers without necessarily stopping you from seeing — from the luminance, size and position of each luminaire against the background. EN 12464-1 sets a limit per activity from the series 16, 19, 22, 25, 28. The 2011 edition wrote that limit as UGRL; the 2021 edition writes RUGL, with the formula unchanged. UGR explained covers the method and where it stops working.
Cylindrical illuminance — Ec in the CIE vocabulary, Ēm,z in EN 12464-1, in lux
The mean illuminance on the curved surface of a very small vertical cylinder at a point in the room: light falling on vertical surfaces from all around, rather than on the desk. It decides whether faces and objects read well; a CIBSE Journal review of the 2021 edition puts the range for good visual communication at 50 to 150 lux, depending on the activity. Since 2021 it sits in the requirement tables, per activity.
Working plane
The reference surface on which work is usually done: the desk or table in an office, the floor in a corridor. It can be horizontal, vertical or inclined. Where nothing more specific is known, the Belgian guide to EN 12464-1 takes a horizontal plane 0.85 m above the floor.
Task area, immediate surrounding area, background area
The three nested zones EN 12464-1 sets its values on. The task area is the part of the work place where the visual task is carried out, and carries the full requirement; where several tasks share a space it is called an activity area. The immediate surrounding area is a band at least 0.50 m wide around it, lit to a level that a table in the standard derives from the task value — it may be lower than the task, but not below that table’s value. The background area is a band at least 3 m wide around that, or up to the wall, taken at floor level, at no less than a third of the surrounding level.
Calculation grid
The points on each reference surface where illuminance is calculated, or measured when the installation is checked. Averages, minima and uniformity are all read off these points, so the grid is part of the result. EN 12464-1 limits the spacing by a formula based on the size of the calculation area; the Belgian guide advises equal spacing in both directions, 0.5 m for any space of 4 m or more, and the same grid whenever two studies are compared.
Photometric file — IES and EULUMDAT (LDT)
A luminaire’s measured light distribution in a text file: its luminous intensity in every direction, plus data such as its luminous flux. IES files follow IES LM-63, the Illuminating Engineering Society’s ASCII format, with candela values per vertical and horizontal angle; EULUMDAT (LDT) is the ASCII format developed for European lighting planners, with intensities given in candela per 1000 lumen. The calculation runs on this file, which is why Momik calculates from real IES/LDT photometry rather than estimates.
Isolux diagram — iso-illuminance lines
A plan of the room with lines joining the points of equal illuminance, like contour lines on a map, so you see at a glance where the light falls off. The CIE now calls these iso-illuminance curves; “isolux” is the older name that reports still use.
Definitions and units: CIE e-ILV (CIE S 017:2020), free to read at https://cie.co.at/e-ilv; symbols as EN 12464-1 writes them (CIE writes Ec for cylindrical illuminance and Tcp for CCT) — e.g. illuminance https://cie.co.at/eilvterm/17-21-060, maintenance factor https://cie.co.at/eilvterm/17-29-146, illuminance uniformity https://cie.co.at/eilvterm/17-29-160. Colour temperature classes, Ra floors, working-plane height, maintenance-factor parts and grid advice: IBE-BIV Guide pratique, November 2023. Zones, per-zone uniformity and the maintained-value rule: same guide, pages 10, 11 and 16; the surrounding-area and background rules also appear in the public preview of the final draft, clauses 4.3.4-4.3.5, https://cdn.standards.iteh.ai/samples/61880/ebce187de6de4f8496424952ac263b64/kSIST-FprEN-12464-1-2021.pdf UGR series, formula terms and the datasheet standard room: ZVEI / licht.de, https://www.licht.de/fileadmin/Publications/ZVEI_Publications/2110_E_ZVEI_UGR_method.pdf — cylindrical range: https://www.cibsejournal.com/technical/work-light-balance-key-changes-to-workplace-lighting-guidance/ — IES LM-63: https://docs.agi32.com/PhotometricToolbox/Content/Open_Tool/iesna_lm-63_format.htm and ANSI/IES LM-63-19, https://webstore.ansi.org/standards/iesna/ANSIIESLM6319 — EULUMDAT: https://docs.agi32.com/PhotometricToolbox/Content/Open_Tool/eulumdat_file_format.htm
The rules in brief: what EN 12464-1 asks
EN 12464-1 is the European standard for lighting indoor work places. It sets what the light has to achieve for the people working under it — visual comfort and visual performance for normal or corrected-to-normal vision — and it sets that per activity. The current edition is from 2021.
Four values per task or activity
Every activity in the tables carries a maintained illuminance Ēm, a minimum uniformity Uo, a minimum colour rendering index Ra and a glare limit RUGL. Since 2021 the same row also carries three values for the room: cylindrical illuminance Ēm,z and the illuminance on walls and ceiling, Ēm,wall and Ēm,ceiling.
Two illuminance columns since 2021
Each row gives a required value, which is the minimum, and a modified value for when the context asks for more — not a maximum. Seven conditions decide it, among them tasks critical for safety or economic value, exceptional precision, observers with poorer vision such as older workers, and unusually long observation times. Where one or two apply, the standard recommends one step up the illuminance scale — for example from 500 to 750 lux; more than two, two steps. The room values move up with it.
Zones, not rooms
Requirements are set per work area, not per room. One open-plan floor can hold desks, a copier corner and a meeting table, each with its own values, and each is checked on its own zone with its surrounding band and background. A floor-wide average proves nothing about any of them.
What else changed in 2021
- Wall, ceiling and cylindrical requirements moved out of the running text and into the tables, per activity.
- Glare requirements adjusted and better explained; the quantity was renamed from UGR to RUG without changing the formula.
- A completely revised section on flicker and stroboscopic effects, and new annexes on non-visual effects and on worked examples.
How compliance is shown
At design stage, by calculation, zone by zone, against the values for that zone’s activity: Ēm as the average over the grid on the reference surface, Uo from the same grid, and the glare rating RUG from the standard’s tabular method, compared with RUGL. After installation, the standard’s verification clause applies: illuminance is measured at the same grid points, while glare, colour rendering and luminaire luminance are normally taken from the manufacturer’s data. Two details decide whether the result holds. First, the maintenance-factor assumptions belong in the study: the 2011 edition already required them to be listed, and the Belgian guide to the 2021 edition says the soiling assumptions are agreed per project with the client. Second, a UGR value from the formula is no compliance proof — ZVEI notes that where the formula replaces the tabular method, the value is not proof that the limits are met, and a point-by-point maximum from software is not comparable with the limits at all.
The values themselves are in the standard, which the national standards bodies sell. For the office rows that public sources print, with those sources named, see office lighting requirements. For the quantities and the 2021 revision in depth, see EN 12464-1 explained; for glare, UGR explained.
Scope, the seven quantities, the two-column mechanism, the seven conditions and the list of changes: IBE-BIV guide, pages 8-10 and 15-18. Per work area and the 500 → 750 lux example: https://www.cibsejournal.com/technical/work-light-balance-key-changes-to-workplace-lighting-guidance/ — maintenance-factor assumptions: IBE-BIV guide, chapter on the maintenance factor, and ETAP, Dossier EN 12464-1 (2012, on the 2011 edition), https://www.etaplighting.com/sites/default/files/uploads/Dossier%20EN%2012464-1_AT_EN_A4_lr.pdf — tabular method: ZVEI / licht.de position paper, pages 7-9 — verification after installation: IBE-BIV guide, chapter 13, pages 41-42.
How a lighting study runs, step by step
The Belgian guide to EN 12464-1 lists the steps the standard gives for working out the requirements per space; steps 1 and 2 below condense them. Steps 3 to 6 are how the calculation itself then runs:
- Plan. Collect the building: dimensions, ceiling heights, surface reflectances, and what happens in each space.
- Zones. Place every task or activity area, pick the activity from the standard’s tables that fits it best, and derive its surrounding band and background. Read the task values — Ēm, Uo, Ra, RUGL — and the room values, and check whether context conditions raise them a step.
- Luminaires and photometry. Choose the luminaires, load their IES or LDT files, set positions and mounting height, and fix the maintenance factor.
- Calculation. Compute the illuminance on the grid of every reference surface, and the glare rating by the tabular method.
- Check against the requirements. Compare every zone with its own values — task and room — not the floor with one number.
- Report. Present the results zone by zone, with the maintenance factor and the grid stated, so a reader can see which zone passes and which does not.
In Momik, a study runs in four steps. Draw or upload your zones, and each type gets the standard values that belong to it. Filter the catalog on your requirements — lux, UGR, IP, CCT, CRI, mounting. Click Calculate for illuminance, uniformity, UGR and isolux per zone; maintained illuminance, uniformity (Uo) and UGR are checked against the standard values for that room type. Receive a standards-compliant PDF report with heat maps, a luminaire list and results per zone.
Design steps: IBE-BIV guide, chapter 12, which lists the steps of clause 6 of NBN EN 12464-1. Grid advice: same guide. Momik’s four steps and the per-zone check repeat the product description and FAQ on https://momik.ai.
Keep learning
- EN 12464-1 explained — the quantities, the 2021 revision and where to buy the official text.
- Office lighting requirements — lux, Uo, Ra and UGR per office task, from public sources.
- UGR explained — how the glare rating is calculated and where the method stops working.
- Online lighting calculation software — what a standards-compliant study in the browser looks like.
- Momik tutorials — video guides to running a study in Momik.