Lighting standards: where the lux requirements come from

Why an office desk gets 500 lux and a corridor 100 lux, what those numbers actually measure and how to apply and check them in a real room.

Anyone reviewing an electrical design sooner or later meets a line like "task area — 500 lx". That figure is not a designer's preference. It comes from lighting standards, and it says that the light reaching the desk must be enough for the eyes to work without strain. Once you understand the logic behind the standards, it becomes much easier to check a design and avoid both wasted power and poorly lit workplaces.

What lux measures

Lux (lx) is the unit of illuminance: the amount of luminous flux falling on one square metre of surface. One lux equals one lumen spread evenly over one square metre. The distinction matters: lumens describe how much light a lamp emits, while lux describes how much of that light actually arrives on a particular surface. The same lamp gives one illuminance on a desk from three metres and quite another from two.

That is why standards talk about results, not lamp power. The requirement is written as "lux on the surface", not "watts per fitting". Choosing the lamps, their number and their positions is simply the route to that result.

Where the numbers come from

For indoor workplace lighting, the most widely referenced document in Europe is EN 12464-1. In Russia and much of the former Soviet region, codes such as SP 52.13330 (the successor of SNiP 23-05) are used. Projects in Azerbaijan follow local building codes, and international projects often apply the European standard directly. The figures in these documents are close to each other because they rest on the same physiological observations: the finer the detail and the longer the task, the more light the eye needs.

Some frequently quoted values from EN 12464-1:

• office desks for writing, reading and computer work — 500 lx;
• corridors and circulation areas — 100 lx;
• stairs — 150 lx;
• technical drawing and precise manual work — 750 lx;
• storage areas in warehouses — 100–200 lx depending on the task.

Homes fall outside the scope of this standard. Residential figures are generally recommendations and depend on how each room is used.

Reading a standard correctly

The value in the table is the "maintained illuminance". It is not the level on the day of installation but the level that must never be undercut during the life of the installation. Lamps lose output over time, fittings collect dust, walls fade. Designers account for this with a maintenance factor and size a new system with some extra light.

The second point is the task area. The 500 lx applies to the zone where the work happens, not to the entire room. The surrounding area may be designed one step lower, which puts energy where it is needed.

Third comes uniformity. Even with an average of 500 lx, a desk that is bright at one corner and dim at the other forces the eye to keep readjusting. Standards therefore also set a ratio between minimum and average illuminance.

Finally, standards are not only about lux. They include quality requirements such as the glare rating (UGR) and colour rendering index (Ra). Offices typically call for UGR below 19 and Ra of at least 80. Light that reaches the right lux level but dazzles people does not comply.

How to check a room

After installation, a lux meter is the simplest way to verify the result. A few rules make the measurement meaningful:

• measure at working-plane height, which in an office is roughly desk level;
• take readings in the evening or with blinds closed to exclude daylight;
• divide the area into a grid and measure several points, then average them;
• keep your body from shading the sensor;
• let new lamps run for a while before measuring so their output stabilises.

Smartphone apps give a rough idea, but their sensors are not calibrated. A formal handover needs a calibrated instrument.

Common mistakes

The most common error is applying one level to the whole building: corridors, archives and desks all get 500 lx and energy is wasted. The opposite also happens — old lamps are swapped for LEDs "watt for watt", light output drops, nobody measures, and staff start complaining about tired eyes.

Another mistake is looking only at the lamp's specification. Ceiling height, wall colour and furniture layout have a strong effect on the result. In a room with light-coloured surfaces, the same lamp produces noticeably higher illuminance than in a dark one.

Standards are the starting point for a calculation, and the luminous flux and other data for each lamp come from the manufacturer's datasheet. Zaferoğlu Elektrik, which makes Zəfər İşığı lamps at its plant in Ganja, lets visitors filter its catalogue by cap and lamp type.