Glare-free High Beam:Optimal Traffic Sign Illumination

Kyriakos Kosmas, Jonas Kobbert, Prof. Dr.-Ing. habil. Tran Quoc Khanh,

Laboratory of Lighting Technology, Technische Universität Darmstadt

With the development of glare-free high beam systems, it is possible to continuously drive with high beam, without inflicting glare on other road users. However, this means that traffic signs are illuminated with high beam as well. Due to their retroreflective properties, the light is reflected back to the driver and may result in glare. This kind of glare is designated as self-glare, since the driver is dazzled by light from his own headlamps. First static laboratory studies have shown, that traffic sign glare-illumination is angular size dependent. While approaching a traffic sign, it appears to get larger, whereby illumination has to decrease in order to avoid glare – especially when driving with glare-free high beam [1]. For this reason, first OEM’s already cut traffic signs out of the light distribution to avoid this effect. Traffic sign luminance is also adapted, since the transition between light environment and dark signs leads to poor legibility [2]. But the question: “What is the optimal illumination to avoid glare and simultaneously allow a high identification?” remains unanswered.

To answer this question, the Laboratory of Lighting Technology at the Technische Universität Darmstadt conducted a field study with subjects, in which two main aspects are considered – identification and glare of traffic signs. This results in a test setup in which a vehicle with glare-free high beam passes with constant speed, traffic signs located to the left and right side of the driver. After passing with low beam (lower limit) and high beam (upper limit), high beam is dimmed stepwise to simulate different levels of masking out traffic signs as explained above. To find the optimal masking level, identification tests are performed for each high beam step. By combining the identification distances with the identification luminance and the deBoer rating, the optimal traffic sign illumination can be found.

Furthermore, illuminance is measured during each passing process, both at the traffic sign and at driver’s eye position. To receive a correlation between measured illuminance and distance, a GPS system is placed on both vehicle and traffic sign. After passing the traffic sign, each driver is asked to rate the glare intensity using the deBoer scale.

[1] P. Schreier, Dissertation, “Untersuchung zur Eingenblendung des Fahrzeugführers durch Streulicht bei Nebel und Schnee sowie durch retroreflektierende Verkehrszeichen“, Ilmenau 2016

[2] C. Neitzke, P. Roeckl, F. Langkabel, T. Feid, “Voll-LED-Scheinwerfer mit Matrixlicht im Opel Astra“, ATZ February 2016