An illuminance survey measures the quantity and distribution of light reaching selected workplace surfaces. Readings are taken at defined positions, heights and orientations so that the results represent the task and its surroundings rather than a collection of convenient or unusually bright points.
Illuminance is the amount of luminous flux received by a surface per unit area. It describes light arriving at a desk, workbench, floor, wall, equipment face or other defined plane. It does not describe the total output of a lamp or the brightness seen when looking towards a surface.
Luminous flux is the total quantity of visible light emitted by a source and is expressed in lumens. A stated lumen output does not produce the same illuminance everywhere. Distance, optical distribution, shielding, room geometry, absorption and reflection affect how much light reaches a particular point.
Luminance describes light leaving or being reflected from a surface in a particular direction. It relates more closely to apparent brightness in the observer's field of view. Illuminance may be measured on a desk to establish how much light reaches a document, while luminance may be considered when examining a screen, window or reflective surface.
These quantities are related but not interchangeable. Two surfaces receiving similar illuminance may appear different because of their finish, colour and reflectance. A workplace may also receive substantial illuminance while still presenting difficult brightness contrasts or glare.
The lux is the International System of Units measure of illuminance. One lux represents one lumen distributed over one square metre. Workplace survey results in the UAE are commonly expressed in lux, although some regulatory documents and project specifications also use foot-candles.
A foot-candle is based on lumens per square foot. One foot-candle is approximately 10.764 lux. Conversion changes only the unit used to express the result; it does not alter the lighting condition or improve the measurement.
The unit should remain clear and consistent throughout a set of readings. Mixing lux and foot-candles without explicit conversion can create apparent differences, especially where values have been rounded. A converted result should reflect the precision of the original reading rather than imply greater accuracy.
Illuminance should not be confused with lamp output. A lumen rating alone cannot establish the lux value at a task because the result also depends on the luminaire, mounting position, obstructions, surface properties and reflected light.
A measurement grid provides a systematic method for sampling illuminance across an area. The survey surface is divided into cells, with readings taken at representative positions. This reduces the risk of concentrating measurements only beneath luminaires, beside windows or at visually convenient locations.
Grid spacing should reflect the dimensions, shape and lighting pattern of the area. A large open floor may permit wider spacing where conditions change gradually. A small task zone, irregular room or area with localised light sources may require closer spacing to reveal meaningful variation.
The number of points should be sufficient to represent the spatial distribution of light. Too few readings may conceal dark patches, bright concentrations or changes near the edges. Very dense sampling at almost identical positions may add data without improving understanding.
Points should represent the occupied or usable space. Locations may need adjustment where walls, machinery, racking or fixed furniture make a nominal point inaccessible or unrepresentative. Any adjustment should preserve systematic sampling rather than select a more favourable result. Distinct zones may need separate grids where an obstruction, change of task or different lighting arrangement divides the area, because combining dissimilar zones can produce an average that represents none of them adequately.
The task area is the part of the workplace where the principal visual activity occurs. It may be a document surface, assembly point, machine control, picking face, inspection surface or another location where visual detail must be resolved.
The task area is not necessarily the whole desk, workbench or work area. Its boundaries should follow the location and extent of the actual activity. Where the task moves, the measured area should represent the normal range of working positions rather than one preferred point.
The immediate surrounding area lies around the task and influences the visual transition between the task and the wider space. Its lighting matters because a pronounced change between adjacent zones can require repeated visual adaptation. Its boundary should reflect the practical relationship between the task and nearby working space.
The background area forms the wider visual environment beyond the immediate surroundings. It may include remaining floor space, walls or circulation areas within the field of view. Measurements in the task, surrounding and background areas answer different questions and should not be treated as though they describe the same surface.
The working plane is the plane on which illuminance is assessed. It should correspond to the surface or position where the visual task occurs. A desk, floor, workbench, equipment panel, shelf face and angled inspection surface may each require a different plane.
Measurement height should follow the real task rather than a generic assumption. Seated desk work, standing bench work, low-level maintenance and high storage inspection occur at different heights. Where no fixed task plane exists, the selected height should represent normal use.
A reading taken above or below the task may differ because of distance from luminaires, shielding by furniture or equipment, and changes in reflected light. Height and orientation should therefore remain consistent across points intended for comparison.
Some activities involve several planes. A worker may view a horizontal document, vertical screen and angled control panel during one task. Separate readings may be needed because combining different planes would obscure the light received by each surface.
Horizontal illuminance is measured on a horizontal plane and is commonly associated with desks, floors, worktops and other upward-facing surfaces. It is appropriate where the principal task lies flat or where general illumination across a horizontal area is being examined.
Vertical illuminance is measured on a vertical plane. It is relevant to shelving, noticeboards, equipment faces, people, security scenes and objects viewed from the side. A space may have well-lit horizontal surfaces while vertical targets remain poorly illuminated because most light is directed downwards.
Cylindrical illuminance represents light arriving around a point from multiple horizontal directions. It considers how people and three-dimensional objects are modelled within a space rather than how much light falls on one flat surface.
The selected orientation must match the visual question. A horizontal reading cannot establish vertical illuminance, and one vertical direction cannot represent light arriving from every direction. The measurement plane should be defined before readings begin and maintained across comparable points.
The light-sensitive cell should be aligned with the plane being measured. For horizontal illuminance, its receiving surface should remain level. For vertical illuminance, it should face the relevant direction. For an angled task, it should follow the task surface.
Tilting or rotating the cell changes the angle at which light reaches it and may alter the result. The sensor should be positioned at the intended point and held still while the displayed value settles.
The surveyor should avoid standing between the cell and a luminaire, window or reflected light path. A body, hand, clipboard or other object can shade the sensor and lower the reading. Positioning should minimise obstruction while keeping the cell at the correct point and orientation.
Clothing can also affect a sensitive reading. Light-coloured or reflective clothing close to the cell may add reflected light, while dark clothing may absorb light that would otherwise reach the point. Comparable readings should therefore be taken without changing sensor height, direction or its relationship to nearby objects. Moving the cell towards a brighter source or lifting it above the defined plane produces a result that no longer represents the selected location.
In the Emirate of Abu Dhabi, workplace lighting is a mandatory matter. The Abu Dhabi Public Health Centre states that Codes of Practice under the ADOSH-SF framework are mandatory to all entities regardless of risk classification, and ADOSH-SF Code of Practice 8.0, General Workplace Amenities, Version 4.0, effective 15 July 2024, applies to all employers within the Emirate of Abu Dhabi. Its Section 3.8 sets minimum illumination intensities of 30, 10 and 5 foot-candles according to area type, which the Code itself converts at approximately 10.764 lux to the foot-candle. ADPHC's Technical Guideline on ergonomics in an office environment adds recommendations for office and screen work and is classified as non-mandatory. At federal level, MOHRE Administrative Decision No. 19 of 2023, Article 4(c), places lighting duties on employers within MOHRE's jurisdiction, including a requirement for emergency lighting when the primary system fails. EN 12464-1 and ISO/CIE 8995-1 are consensus standards: widely used and often specified contractually, but not statutory in the UAE unless an instrument adopts them. A requirement binding only in the Emirate of Abu Dhabi is not UAE law and must not be described as such.
ADOSH-SF Code of Practice 8.0 — General Workplace Amenities, V4.0 (15 July 2024), Section 3.8; MOHRE Administrative Decision No. 19 of 2023, Article 4(c)
Lux describes illuminance received by a surface, while lumens describe the total luminous flux emitted by a source. A lumen value characterises light output; a lux value describes how that output is distributed onto a particular area.
Illuminance usually varies across a room because of luminaires, daylight, distance, furniture, partitions, machinery and reflections. A grid of readings shows the spatial pattern more reliably than a single measurement.
No. Readings should be taken on the plane where the relevant visual task occurs. The floor may suit circulation areas, but desks, benches, vertical panels and inspection surfaces require measurements aligned with their task planes.
No. Horizontal and vertical illuminance describe light reaching differently orientated planes. A horizontal reading may represent a desktop but cannot establish the illuminance received by shelving or an upright control panel.
The surveyor may block direct or reflected light reaching the cell or introduce additional reflection from clothing and equipment. Positioning should minimise both shadowing and unintended reflected light.
No. An average combines several readings into one value and does not show the full distribution. Individual grid results remain necessary for identifying localised bright and dark areas.