Establishment of a photometric laboratory for testing and assessing the luminance of self-illuminating visibility clothing

Status:

completed 12/2021

Aims:

On conventional high-visibility clothing according to DIN EN ISO 20471, retroreflective sections of the clothing must ensure that the wearer is visible from all sides (360-degree visibility) in the dark. However, this high-visibility clothing is only effective when it is illuminated by an external light source. In the absence of an external light source, this high-visibility clothing is largely ineffective. The proposed remedy for this situation is the use of self-illuminating high-visibility clothing. Active (self-illuminating) lighting elements such as LEDs are proposed as a way to fill this gap even in diffuse lighting conditions. High-visibility clothing is mainly used by road workers, on construction sites, in port handling or in internal transport.

The Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA) was commissioned by the German Social Accident Insurance Institution for Commercial Transport, Postal Logistics and Telecommunication (BG Verkehr) to carry out basic tests for self-illuminating high-visibility clothing and accessories (such as helmets, signal tape or headlights).

Previous findings from field tests, surveys of test persons and measurements of various lighting elements (LEDs, fibre optic lighting and OLED surfaces) were incorporated into a pre-standard (DIN SPEC 91418) by the IFA and actively promoted. Furthermore, a framework that can be used by the initiating German Social Accident Insurance Institution to categorise the luminous intensity/illuminated area of a light source according to the distance from which it is still visible was integrated into the standard.

High-visibility clothing falls under the PPE Regulation, and is therefore subject to approval. Up until now, there has been no suitable and standardised measuring and testing method for determining luminance while taking into account the illuminated area and distance.

The establishment of a photometric laboratory is necessary in order to carry out research and development on the subject of illuminated surface areas and lighting elements and subsequently be able to perform examinations and tests on active (self-illuminating) high-visibility clothing and assess which lighting elements are appropriate for such clothing.

By developing this method for measuring luminance and establishing it in the standard, the IFA is uniquely qualified in the performance of such tests.

Activities/Methods:

The process of establishing the laboratory can be divided into three steps. In the first step, the space was made usable by making the necessary building-related adaptations. This involved coating the ceiling and the walls with non-reflective paint that enables extremely dark conditions and laying a floor mat to minimise slipping and reflection. The residual reflection had to be significantly lower than 1 percent.

In the second step, the actual test set-up was installed. This included purely mechanical mounting of the test set-up using profiles, which satisfied the relevant requirements, including those mentioned above. The optical measuring system featuring a camera and the appropriate mounting elements must satisfy a wide range of technical requirements. For example, the camera must have a sufficiently high resolution of five megapixels (2448 x 2048 pixels) or more and must be able to capture larger fields of view (height x width: min. 0.5 m x 0.5 m, max. 2 m x 1.8 m) and a distance range of min. 0.5 m to max. 5 m.

The first tests on high-visibility clothing equipped with light sources showed that they are concealed by the hand, arm, body movements, bags carried over the shoulder or shoulder straps, which means that the targeted 360-degree visibility specified in the relevant standard is not ensured. In the future, it will be possible to reliably quantify this in this laboratory. Further laboratory tests will provide insights into the visibility of light source of different colours, luminance, brightness, dazzling and the beam angle.

In order to be able to perform measurements across the full 360 degrees around the radiation/reflection source, a photography turntable system (rotating plate with rotary encoder and drive unit) was installed to capture the test objects. This system is linked to the camera via an interface. In order to ensure this turntable system could be used universally, it needed to have a load-bearing capacity of at least 30 kg. As a logical approach for determining 360-degree visibility, measurements were performed in increments of 30 degrees. The complete turntable system was inherited from a previous research project.

In the final step, the components were set up and calibrated. During this process, the aim was to achieve accuracies within 1 cm for the length distances and 1 degree for the resolution.

Results:

During this project, a laboratory for measuring the luminance of self-illuminating high-visibility clothing and accessories was planned and constructed. The laboratory is now used to perform the relevant measurements and tests. Thanks to the way the space is set up, virtually all extraneous light and reflections are blocked out. For the measurement of the 360-degree visibility that the standards stipulate as a requirement for high-visibility clothing, the test specimens can be positioned on a turntable and rotated at 1-degree intervals. The provided camera measurement system is attached to a wall rail system, which allows for adjustments in the X, Y and Z directions. In combination with the turntable, this makes it possible to achieve any measurement position. The measurement distance between the test specimen and the measurement system can be infinitely adjusted between just a few centimetres and 5 metres. The new, expanded certification procedures within the scope of accreditation for protective clothing have already been included in the IFA’s (Institute for Occupational Safety and Health of the German Social Accident Insurance) list of standards/procedures within the flexible scope of accreditation. Following this project, testing principles for the testing and assessment of self-illuminating high-visibility clothing will be created. These testing principles will be the focus of a follow-up project. This will be followed by the creation of relevant test instructions and work instructions. In addition, all parameters involved in the measurement must be subjected to a measurement uncertainty evaluation

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