On conventional high-visibility clothing to EN ISO 204711, retroreflective elements are intended to ensure 360° visibility of wearers in the dark. Such clothing is however largely ineffective when it is not illuminated by an extraneous light source. Luminous high-visibility clothing could be the solution. The Institute for Occupational Safety and Health of the DGUV (IFA) has tested the effectiveness of such clothing and is submitting the results to development work on a pre-standard.
Good visibility is crucial to safety in many areas, such as in road traffic, on construction sites, in in-plant transport and traffic, during port handling operations or at airports. However, under diffuse light conditions or in shadow, workers are not always clearly visible even when wearing high-visibility clothing. To overcome this deficit, manufacturers are working on solutions for luminous high-visibility clothing.
The IFA was tasked by the German Social Accident Insurance Institution for the transport industry (BG Verkehr) with conducting basic studies into the requirements to be met by luminous high-visibility clothing used in road traffic and in-plant transport and traffic. This included study of the minimum number of LEDs and their position, and visibility at night. Issues concerning colour, brightness, glare and beam angle of LEDs are still unresolved. Further aspects yet to be studied are battery safety and battery life, which are decisive factors determining the availability of active illumination, and electromagnetic compatibility (EMC) and electromagnetic fields (EMF) for wearers of implants, electrical safety, degrees of ingress protection, mechanical requirements and cleaning of the clothing.
Visibility tests involving test persons
Lamps such as LEDs, LED strips and fibre optic lighting in a range of designs and colours were evaluated in an initial series of tests with regard to their luminance2 at different beam angles. For this purpose, free-field tests were conducted in darkness with test persons in order to determine the visibility of different LED arrays (in rows or in panel form), luminances (600 cd/m2 and
1,200 cd/m2) and colours (red and yellow) at distances of 50 m, 80 m, 100 m and 150 m.
LEDs arranged on a board at intervals of 3.5 cm and 10 cm were visible to all test subjects up to a distance of 150 m from the light source at a comparatively low luminance of 600 cd/m2. 80% of the test subjects detected the red LEDs more clearly than the yellow LEDs. 20% stated that they were dazzled at close range (distance of 1 m) by glare from the light source with a luminance of 1,200 cd/m². Conversely, a luminance of 600 cd/m2 did not cause glare.
Further tests on high-visibility clothing fitted with LEDs showed that the lamps were partially concealed by the hand, arm, body movements, bags carried over the shoulder or carrying straps, as a result of which the desired 360° visibility is no longer guaranteed. This must be avoided by an adequate number and appropriate arrangement of the lamps.
A second survey of test persons under dark conditions examined different arrangements of LEDs and their visibility from different distances. Only at a luminance of 100 cd/m² or greater were individual red and yellow LEDs fitted at intervals of 17 mm detected up to a distance of 150 m. White LEDs were not visible. The corresponding tests for LED panels are still pending.
A study of the visibility of LED arrays under more realistic conditions was carried out with a class 3 high-visibility jacket on which individual yellow LEDs were arranged at intervals of 10 cm parallel to the existing retroreflective strips. Owing to rigid application of the LEDs not being possible, folds, masking and the selected interval between LEDs, the jacket was visible only up to a distance of 50 m at 400 cd/m². At lower luminances, it was not visible at all.
Pre-standard in progress
The preliminary results are being incorporated into the development of a pre-standard defining particular requirements upon luminous high-visibility clothing, supplementing the existing retroreflective and fluorescent panels on high-visibility clothing in accordance with EN ISO 20471. The pre-standard is intended to permit a swift response to market needs, particularly to the need for testing and certification in accordance with the PPE Regulation3. Plans are for the draft DIN/TS 91418 to be submitted to public enquiry in the first half of the year. Publication of the pre-standard is anticipated at the end of 2020.
O. Mewes, C. Walther, Ch. Werner, W. Grommes (IFA), M. Dauber (BG Verkehr), M. Thierbach (KAN)
1 EN ISO 20471, High visibility clothing – Test methods and requirements
2 Luminance is the only basic photometric quantity that is perceived by the eye. It describes the perceived brightness of a light source and of a surface, and is measured in candela per unit area (cd/m²).
3 Regulation (EU) 2016/425 on personal protective equipment