Workplace Lighting Levels and Measurement

Why measure lighting?

The complaint "it's a bit dim in here" is often closed with a bulb change. Yet poor light is a risk that ranges from slips and trips to machine accidents, and from eye strain to quality defects. Lighting measurement turns this complaint into a number and shows which areas fall short of the standard.

The legal side is brief. Under Annex 1 of the Regulation on Workplace Buildings and Annexes:

• Art. 22: workplaces should be adequately lit by daylight; where this is insufficient, and for night work, suitable and adequate artificial lighting is provided. TS EN 12464-1 is the basis for lighting.
• Art. 23: lighting systems in work areas and passageways are chosen and positioned so as not to create a risk of accidents.
• Art. 24: where failure of the lighting could create a risk, emergency lighting connected to a separate power source is provided.

The regulation does not set a periodic measurement frequency for lighting. The need for measurement is determined by the risk assessment: eye strain complaints, precision assembly, quality control, a new layout or a change of light fittings are good reasons. We look separately at which measurements are mandatory in which situations in our article on workplaces where exposure monitoring is mandatory.

Workplace lux levels: offices, production, warehouses, quality control

TS EN 12464-1 gives a maintained value (Em) for each task and area: the value below which the average illuminance in the task area must not fall over the life of the lighting system. A newly installed fitting gives more light than this value; Em must still be met even when the light decreases with dirt and ageing. The current edition of the standard also defines higher "modified" values to be used when the visual difficulty of the task increases.

The table below collects frequently used rows from the standard's tables. Uo is the ratio of the lowest measured value to the average and shows how evenly the light is distributed over the area.

Warehouse sections with a desk or bench that is used continuously should be lit above the general warehouse value in the table. In colour inspection, not only the quantity of light but also colour rendering matters; the standard calls for a light source with high colour rendering (Ra 90) for this task.

A single value is not enough for office lighting levels: 500 lux on the desk does not mean there is no reflection or glare on the screen. For screen positioning and glare, see our articles on working with display screen equipment and office ergonomics.

Task area, surroundings and background

The standard requires light to be at a certain level not only on the desk but also around it. The eye tires if it constantly has to adjust between a very bright task area and dark surroundings. The values for the immediate surroundings of the task area and for the background are graded as follows:

Uniformity should be at least 0.40 in the immediate surroundings and at least 0.10 in the background. In practice, this means that putting a powerful lamp on the quality control table and leaving the rest of the hall dark is not the right solution.

Measuring points and method

We plan measurements with authorised laboratories; even so, it helps to know the method so you can read the results correctly:

1. Separate the areas. The task area (desk, bench, inspection surface), immediate surroundings, background and passageways are assessed separately.
2. Set the measurement plane. Measurement is taken at the height where the task is carried out: the desk surface, bench surface or the plane of the part being inspected. In passageways, floor level is used.
3. Fix the points. The points are either those defined in the lighting design or a regular grid spread across the area. Repeat measurements are taken at the same points; otherwise two measurements cannot be compared.
4. Record the conditions. All fittings must be working, the effect of daylight during measurement should be noted, and the shadow of the person measuring must not fall on the sensor.
5. Use a calibrated instrument. The lux meter must have a valid calibration certificate.
6. Calculate and compare. The average illuminance and uniformity (lowest value / average) are calculated; neither may be below the value in the table.

Worked example. Suppose 520, 480, 610, 450, 540 and 400 lux are measured at six points on an office desk. The average is 3,000 / 6 = 500 lux; since the lowest value is 400, uniformity is 400 / 500 = 0.80. The desk meets both criteria. Now suppose that on the same business's quality control table, 680, 720, 610 and 650 lux are measured at four points. The average is 2,660 / 4 = 665 lux; although uniformity is good (0.92), it is below the 750 lux required for drawing and inspection work. The solution is to increase general lighting or add task lighting while keeping the balance with the immediate surroundings.

The results are entered into the risk assessment; after corrective action, measurements are repeated at the same points.

Emergency lighting rules

The darkness that falls when the power is cut is one of the factors that makes evacuation hardest. Art. 72 of the Regulation on the Fire Protection of Buildings sets out this framework for emergency lighting:

• The system switches on automatically when the mains supply fails, when power is cut for safety reasons or when a fuse trips.
• It is mandatory on all escape routes, at assembly points, in workshops and laboratories containing high-risk moving machinery and chemicals, in electrical distribution and generator rooms, at pump stations, and where first aid and safety equipment, fire alarm call points and fire hose cabinets are located.
• When normal lighting fails, it operates for at least 60 minutes, or at least 120 minutes if the occupant load exceeds 200.
• The illuminance on the centre line of the escape route is at least 1 lux; at the end of the operating period it does not fall below 0.5 lux at any point. The ratio between the highest and lowest values does not exceed 40.

Risks of poor lighting

The risk in an area with a low measurement result depends on how the area is used. In the risk assessment, address the following headings separately:

• Slips, trips and falls: in dim passageways, liquid on the floor, cables or changes in level are not seen. For details, see our article on preventing slips, trips and falls.
• Forklift and pedestrian traffic: a pedestrian in shadow between racks and at ramp entrances is noticed late by the operator. For warehouse layout, read our article on forklift and pedestrian traffic plans.
• Errors at the machine: moving parts, adjustment points and gauges are misread if there is not enough light. Under flickering light, a rotating part can appear to have slowed down or stopped.
• Eye strain and headaches: complaints increase especially at screens and in prolonged fine work; the workplace physician may link these complaints to the need for measurement.
• Quality and colour defects: insufficient light, or light with poor colour rendering, causes surface defects and colour differences to be missed.

In office and retail workplaces such as shops and offices, lighting is often thought of as purely a comfort issue; yet back-of-house storage areas and stairs are the most neglected points in these workplaces too.

Frequently Asked Questions

How many lux should office lighting be?

Under TS EN 12464-1, for office tasks such as writing, reading and data processing, the maintained value in the task area is 500 lux, with uniformity of at least 0.60. The value for corridors is 100 lux.

Is lighting measurement mandatory?

The Regulation on Workplace Buildings and Annexes requires adequate lighting and takes TS EN 12464-1 as its basis, but sets no periodic measurement frequency. The need for measurement is determined by the risk assessment; measurement is recommended where there are complaints, precision work or changes in layout.

At what height is lighting measured?

In the plane where the task is carried out: on the desk surface, bench surface or the plane where the part being inspected sits. In passageways, floor level is used. Repeat measurements should be taken at the same points.

Can we take measurements ourselves with a lux meter?

For your own checks, a lux meter helps you find problem areas. However, measurements used as the basis for the risk assessment should be taken with a calibrated instrument, at defined points and under recorded conditions; we plan these measurements with authorised laboratories.

How many minutes should emergency lighting stay on?

Under the Regulation on the Fire Protection of Buildings, at least 60 minutes; at least 120 minutes where the occupant load exceeds 200. The illuminance on the centre line of the escape route should be at least 1 lux.