Measuring and verifying lighting installations
Architects and lighting designers have professional tools at their disposal for the verification of lighting installations. In practice, they are mostly employed to measure illuminance. The measuring instruments used simulate the sensitivity of the human eye.
Measurements are taken to
- verify the quality of lighting delivered by projected new installations
- check the state of existing lighting installations and identify the need for maintenance or repair
- compare different lighting installations.
- Illuminance E (e.g. as horizontal illuminance Eh, semi-cylindrical illuminance Ehz), vertical illuminance Ev, as cylindrical illuminance Ez or
- Reflectance ρ (e.g. for ceilings, walls, floors of indoor work premises and indoor sports facilities),
- Reflectant characteristics of road surfaces (e.g. in road and tunnel lighting),
- Mains voltage U and/or ambient temperature ta (where lighting installations feature lamps with a luminous flux that depends on operating voltage and/or room or ambient temperature).
Preparations for measurement
Measuring illuminance calls for instruments that are adjusted to the spectral brightness sensitivity V(λ) of the human eye. They must also be cosine-corrected to ensure the correct evaluation of oblique incident light.
Before any measurement is performed, the following need to be established:
- geometrical dimensions of the lighting installation
- type of installation or room and activity
- variables to be measured and location of measuring points
- general condition of the installation (e.g. age, date when last cleaned, last lamp replacement, degree of soiling).
In addition, the lamps of an installation need to be sufficiently seasoned. Any interference by ambient light should also be ruled out (e.g. daylight in the case of indoor lighting, vehicle lights in the case of outdoor lighting) and any disturbance due to obstacles or measurers' shadows should be avoided.
Creation of a measurement grid
To measure illuminance values, the area of the installation assessed is divided into a grid of equal-sized, preferably square measuring surfaces. The grid dimensions must not be the same as those of the luminaire arrangement. If this were the case, measurements performed directly underneath luminaires, for example, would show only maximum values. However, lighting and room (or outdoor area) symmetry can usefully reduce the amount of measurement.
As a matter of principle, a measurement record should be created for each examination. As well as the values established, it should include details of the environment, lamps, luminaires and geometry of the lighting installation.