Lighting for road tunnels: The influence of CCT of light sources on reaction time

doi:10.1016/j.displa.2019.101931

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Volume 61, January 2020, 101931

https://doi.org/10.1016/j.displa.2019.101931 Get rights and content

Highlights

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The influence of CCT of light sources of road tunnels on human visual performance was invested using reaction time.
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Reaction times were measured under different values of correlated colour temperature (CCT) with a scale model that can simulate an interior road tunnel lighting environment.
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The visual performance can be improved by increasing the CCT of the light sources, the improvement of visual performance is greater in peripheral vision than that in foveal vision.

Abstract

Drivers’ visual performance is closely related to traffic safety in a real driving environment. In order to improve the traffic safety of road tunnel lighting, the effect of LED lighting on human visual performance was investigated using reaction time as a parameter. The experiment was performed with a scale model that can simulate a road tunnel lighting environment. Reaction times were measured under different values of luminance, correlated colour temperature (CCT), eccentricity, and contrast. The results show that visual performance can be improved by increasing the CCT of the light sources. The improvement of visual performance is greater in peripheral vision than that in foveal vision. The shortest reaction times were measured at a luminance level of 10 cd/m² and at a CCT of 5000 K. An appropriate luminance value with high CCT is recommended for tunnel lighting in interior and transition zones.

Introduction

A tunnel is a tubular semi-enclosed traffic area. Tunnel lighting regulations are complex, with different lighting level requirements for different zones [4]. Indeed, these lighting regulations have different effects on drivers’ visual performance, and this can induce traffic accidents. Once a traffic accident occurs, the consequences are extremely serious. For example, on March 1, 2014, a traffic accident in the Shanxi Yanhou tunnel in China caused the death of 40 people and injured 12 others. The direct economic loss amounted to US $12 million [14]. Another recent traffic accident in the Hachihonmatsu tunnel in Japan on March 17, 2016 resulted in the death of 2 people with 70 people injured [9]. Thus, it is important to improve the traffic safety of road tunnels by improving the drivers’ visual performance. In addition, lighting must be provided in tunnels 24 h a day. The electrical consumption statistics of the Chongqing Highway tunnel shows that the average annual cost of electricity in the tunnel is US $62,000 per kilometer, and the total annual electrical cost of road tunnels in China is US $1 billion, of which lighting accounts for ~30% [18]. As tunnel lighting consumes a notable share of total energy, it is imperative to research tunnel lighting from the perspective of traffic safety and energy savings.

The current tunnel lighting standard includes the recommended values for luminance, luminance uniformity, and threshold increment for different tunnel zones [4]. However, these luminance parameters based on photopic photometry cannot reflect the spectral sensitivity at low light levels [10], [13]. At the same time, the colour characteristic described with the CCT and the general colour rendering index (CRI), which is defined by the spectral power distribution, is also a factor that affects visual performance [21]. Therefore, the current lighting standards may not be appropriate for improving traffic safety in tunnels.

Many studies [5], [6], [8], [11] have been conducted to determine the relationship between lighting characteristics and luminance level. McCloughan et al. [11] studied the systematic influences of lighting on the driver’s mood using lighting parameters such as CCT. They demonstrated that lighting quality has initial effects, linking illuminance with sensation-seeking and CCT with hostility, and longer-term effects, implying complex effects involving gender, illuminance, and CCT. Suzer et al. [16] studied the effects of CCT on wayfinding in a virtual airport environment, the wayfinding performance were evaluated in five criteria: Time spent in finding the final destination, Number of errors in finding the final destination, Number of decision points necessary to find the final destination, Number of hesitation points in finding the final destination, and Route choice, which indicated that the CCT have significant effect on the frequency of experiencing hesitations and the number of hesitations decreased when CCT increased from 3 000 K to 12 000 K of the male test subjects. Meanwhile, the user acceptance in LED office lighting was studied by Islam et al. [8]. They showed that spatial brightness is affected by the spectral power distribution (SPD) of the lamps, and observers preferred the task illuminance in which they found the lighting environment appeared brighter. Research of lighting for subsidiary streets was carried out by Fotios and Cheal [5], [6] who showed that reduced visual performance can be compensated by the SPD of the lamps.

Only a few studies based on visual performance have been conducted regarding tunnel lighting. In the study by Liu et al. [20], LEDs (in five different CCTs: 2432 K, 3686 K, 4446 K, 4806 K, and 5128 K) and other two traditional light sources (a high pressure sodium lamp in 1919 K and a metal halide lamp in 2789 K) were studied at three light levels (4.5 cd/m², 45 cd/m², and 85 cd/m²). They showed that the influence of light source CCT and optical biological effects must be considered when choosing suitable light sources in different sections of tunnel lighting. The visual performance of different light sources in the mesopic level (1–5 cd/m²) was studied by Yang et al. [19], who showed that visual recognition in mesopic level evaluated by using the photopic function is an inappropriate method, and that the increase of CCT (from 1958 K to 5537 K) can improve the reaction speed in the mesopic level. However, there is no similar study conducted on the influence of CCT on foveal and peripheral vision in the mesopic range and in the level from photopic to mesopic (from dozens of cd/m² to 1 cd/m²), which is very important in the transition and interior zones of a tunnel. There is little research on visual performance influenced by the spatial brightness in road tunnel lighting in previous studies.

Road tunnel lighting resembles road lighting, but has its unique requirements due to the entrance and exit of the tunnel. In order to study the relationship of CCT, spatial lighting (i.e., tunnel lighting), and visual performance, a 3D scale model was developed to simulate the real tunnel lighting environment. With the reaction time measurement devices, this study focuses on the relationship between reaction time and the CCT of tunnel light sources, which is regarded as a suitable starting point to improve tunnel lighting quality. It is expected that this study will provide a new method to optimize the existing design methods of tunnel lighting, and to make the tunnel lighting environment conform better to actual visual performance.

Section snippets

Design of test system

For the complex lighting environment in the highway tunnel, the driving task mainly includes four processes: preview, perception, judgment, and response. In the above mentioned four tasks, the driver's preview-perception process is mainly affected by the road tunnel lighting environment, and this is of great significance to traffic safety, and relates to the timely detection of other traffic targets and vehicle scheduling. This paper focuses on the influence of the tunnel lighting environment

Results

The reaction times of each test subject were obtained under different conditions through the procedures of the experiment. The mean reaction time of the 54 test subjects was calculated, and is shown in Appendix A1. The data was analyzed according to different test conditions. To simplify the data analysis, the eccentricities of 20° and −20°, as well as −10° and 10°, were considered to be the same.

The eccentricity values were 0°, 10°, and 20°; the contrast ratio values were 0.2 and 0.5; and the

Discussion and conclusions

The CCT of the tunnel light sources and reaction time are inversely proportional. The reaction time can be shortened and the visual performance can be improved with the increase of CCT values of the light sources within a certain range (from 3000 K to 5000 K). The foveal and peripheral visual performance are both improved with higher CCTs of light sources. The improvement in the peripheral vision is greater than that in the foveal vision (Table 5). The decrease of the mean reaction time is

Declaration of Competing Interest

There are no conflicts of interest.

Acknowledgements

This research work was sponsored by the Project of the National Natural Science Foundation of China [Grant No. 51678096, 51878107], the Basic Research and Frontier Exploration Project of Chongqing (cstc2018jcyjAX0118), the Science and Technology Research Program of Chongqing Municipal Education Commission (KJQN201800734), the Open Funding of State Key Laboratory of Mountain Bridge and Tunnel Engineering (SKLBT-19-008).

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View full text

Lighting for road tunnels: The influence of CCT of light sources on reaction time

Highlights

Abstract

Introduction

Section snippets

Design of test system

Results

Discussion and conclusions

Declaration of Competing Interest

Acknowledgements

Contrast threshold measurements of peripheral targets in night-time driving images

Light. Res. Technol.

Reaction time measurements under mesopic light levels: towards estimation of the visual adaptation field

Light. Res. Technol.

Correction: lighting for subsidiary streets: investigation of lamps of different SPD. Part 2 – brightness

Light. Res. Technol.

Lighting for subsidiary streets: investigation of lamps of different SPD. Part 1–-Visual Performance

Light. Res. Technol.

User acceptance studies for LED office lighting: lamp spectrum, spatial brightness and illuminance

Light. Res. Technol.

Simple time reaction as a function of luminance for various wavelengths

Percept. Psychophys.