Energy Savings in Tunnel Lighting by Improving the Road Surface Luminance Uniformity—A New Approach to Tunnel Lighting—

Abstract

The authors propose a new method for tunnel illumination using LED lights. The luminous characteristics of tunnel lighting employing LED luminaires were measured in the Shiratori tunnel on the Japanese expressway. The results show that this method achieves over 0.9 of luminance uniformity. Moreover, the visual impression evaluation that was conducted using 29 subjects, shows that roads with over 0.9 luminance uniformity and luminance of 2.3 cd/m 2 , have equivalent or better visibility than roads with low uniformity and luminance of 3.5 cd/m 2. This result suggests that the High Luminance Uniformity Method which we propose could save up to 20 of the energy used for illumination and improve safety due to higher visibility.

Impacts of average illuminance, spectral distribution, and uniformity on brightness and safety perceptions under parking lot lighting

“…In the field studies by Boyce et al 1 and by Rea et al, 13 the uniformities of the installations that were evaluated were representative of North American lighting practices 14 (which use the ratio between the maximum and minimum horizontal illuminance to define uniformity, rather than the ratio between the average and minimum illuminance) with maximum:minimum illuminances of 10:1 or 20:1 being typical, 14 but uniformity was not explicitly studied by those researchers. Kimura et al 15 reported that more uniform distributions of light could result in lighted tunnels being perceived as brighter than installations with higher average light levels but less uniformity. Nasar and Bokharaei 16 reported that observers preferred outdoor lighted scenes that were illuminated more uniformly, and Fotios et al 17 found larger differences between daytime and nighttime safety ratings for street lighting installations under more non-uniform nighttime lighting.…”

“…Kimura et al . 15 reported that more uniform distributions of light could result in lighted tunnels being perceived as brighter than installations with higher average light levels but less uniformity. Nasar and Bokharaei 16 reported that observers preferred outdoor lighted scenes that were illuminated more uniformly, and Fotios et al .…”

Integrating Research on Safety Perceptions Under Parking Lot Illumination

“…As stated above, the impacts of uniformity of outdoor illumination have not been extensively studied, although lighting recommendations (e.g., IES, 2018) include limits on the uniformity ratio for parking lot lighting. Because of anecdotal observations that LED outdoor lighting systems might be able to produce more uniform illumination (with lower max:min ratios) and because LEDs tend to have small source sizes that in principle, are conducive to the design of efficient optical systems that could produce uniform illumination, Narendran et al (2016) conducted a study to assess whether, as suggested by Kimura et al (2014), more uniform lighting could increase perceptions of scene brightness and hence safety and security, than more non-uniform lighting.…”

“…According to these recommendations (IES, 2018) the max:min illuminance ratio upper limit is specified to ensure that an observer standing in the brightest portion of a parking lot can see within the darkest portion of the lot. Little empirical research has been published on the impacts of parking lot or road illumination uniformity on perceptions of safety, however; Kimura et al (2014) found that more uniform illumination in a tunnel contributed to increased perceived brightness, which should in turn (Rea et al, 2009) influence perceptions of safety.…”

Effective Lighting Factors for Improving Visibility of Fallen Objects on the Road in Expressway Tunnels

“…Recently, several studies have improved the visibility in tunnels using light-emitting diode (LED) luminaires (Kimura et al, 2014(Kimura et al, , 2019Hirakawa et al, 2014Hirakawa et al, , 2015. LEDs provide more freedom in the lighting design than conventional light sources.…”