Uniformity (Uo) is the ratio of the minimum illuminance measured on a surface to the average illuminance value. This parameter indicates whether light is distributed evenly or whether significant differences exist between brighter and darker areas.
When interpreting a report, the Uo value should be reviewed alongside the number of measurement points and the boundaries of the assessed area. Only by considering all of these factors together can you determine whether appropriate lighting conditions are provided across the entire task area.
Commissioning measurements verify whether a completed installation meets the original design requirements. Follow-up inspections reveal the effects of operation, contamination, ageing of light sources, or changes in workspace layouts.
Lighting designs incorporate a maintenance factor, which accounts for the gradual reduction in lighting performance over time and helps ensure that the required lighting levels are maintained throughout the intended service period. Results from periodic inspections should be compared with project documentation, and measurement conditions should always be recorded. This makes it possible to determine whether routine maintenance is sufficient or whether modifications to the installation are required.
The difference between on-site measurements and calculations performed in DIALux or Relux lies in the fundamentally different nature of these methods.
Lighting calculations are predictive models based on luminaire photometric data, room geometry, surface reflectance properties, and the selected maintenance factor. A measurement, on the other hand, reflects the actual condition of the installation at a specific point in time.
Results may be influenced by daylight, dirt accumulation, obstacles, luminaire positioning, and differences between the real environment and the design model. A measurement report documents real-world conditions, while a lighting simulation helps evaluate the suitability of the proposed design solution.
The measurement grid defined by EN 12464-1 provides a structured method for collecting readings that accurately represent the entire assessment area. The spacing of measurement points depends on the dimensions of the area and the requirements of the selected methodology.
To determine the maximum grid spacing, the following relationship is used:
p = 0.2 × 5^log10(d)
where d is the longer dimension of the assessed area, expressed in metres.
This value should be interpreted in accordance with the relevant standard requirements and measurement procedures. The measurement grid should be established before testing begins, and its layout should be documented in the report. This facilitates future repeat measurements and helps identify areas where the greatest deviations occur.
The task area and its surrounding area should be assessed separately because the work surface itself and the adjacent environment may be subject to different lighting requirements.
The task area covers the zone where visual tasks are performed, while the surrounding area affects orientation, visual comfort, and the perception of contrast. Measurement points should reflect the actual workstation layout rather than only locations that are easy to access.
The report should clearly identify the boundaries of each zone, the height of the measurement plane, and any obstacles that may affect light distribution.
The class of the lux meter and its cosine correction characteristics have a direct impact on the reliability of measurement results.
The instrument should be suitable for the required level of accuracy, in proper working condition, and covered by valid calibration or verification documentation in accordance with the applicable procedure. Cosine correction ensures that the sensor responds correctly to light arriving from different angles.
During measurements, the sensor head should be positioned on the correct measurement plane and must not be shaded by the operator or nearby equipment.
A complete measurement report should include:
- Identification of the measuring instrument
- Date and location of the measurement
- Recorded results
- Assessment criteria
This information ensures that the document can be used as a reliable reference during future inspections.
When reviewing measurement records, data consistency is equally important. The report should specify whether measurements were carried out under electric lighting only, whether daylight was taken into account, and whether all luminaires intended for the assessed zone were operating during testing.
Any unusual circumstances should also be documented, such as the temporary shutdown of part of the installation or the presence of objects obstructing the light output. This makes it easier to compare results over time and accurately assess changes in lighting performance.
At Lena Lighting, we combine Polish manufacturing expertise, technological innovation, and extensive experience in designing professional LED lighting solutions. We continuously develop energy-efficient luminaires and lighting control systems, focusing on quality, durability, and sustainability objectives.