On-Demand Tunnel Lighting System Utilizing Daylight: A Case Study
, Pramod Bhusal 4, Zeyu Hou 2 and Chaoyu Zhang 2Round 1
Reviewer 1 Report
I have reviewed this article which deals with a case study of tunnel’s renewable lighting in China
The topic is interesting and well researched and I consider that this article is appropriate for scientific knowledge in Sustainable infrastructures.
The combination of electric lighting and daylighting by optical fiber is rather promising.
The methodology discusses the objective features of their findings by means of original algorithms although the authors have not added comparisons with other similar elements in China. Perhaps adding more plans and sections of the tunnels to be discussed would add to the readability of the article.
The design strategies are highly developed.
In general the article is complete and thoroughly researched, some details of the economic repercussion and cost-effectiveness of the interventions could be necessary in the next stage.
The conclusions are consistent but perhaps could be slightly be expanded with adding more case studies in the future.
Summary of evaluation: This article sets an interesting evolution for daylighting of tunnels in China. My suggestion is that the article should be published after minor adjustments.
Author Response
We thank the reviewers for their comments that helped us improve the quality of the manuscript.
In order to increase the readability of this study, we added the size of the test tunnel and the internal scene information in Section 3.1, as shown in Figure 6 and 7. It is worth pointing out that the experimental tunnel was constructed according to the 1:1 size of the actual two-lane tunnel in China. Therefore, the research results can be applied to the actual operating tunnel directly.
As suggested by reviewers, we are looking for suitable tunnels, such as Zengjiayan Tunnel in Chongqing, China, to carry out research and application, so that they can be widely used in the future. At the same time, we also add this discussion to the research outlook of the conclusion.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors reported a lighting scheme of highway tunnels using optical fibers to guide sunlight into tunnels. This study reduces lighting energy consumption and improves driving safety through the utilization of sunlight and the dynamic control of LED brightness. Overall, the topic is within the scope of Sustainability, and the manuscript is well-written. I would recommend a minor revision, provided that the following concerns are addressed.
(1) It seems that the coupling efficiency and transmission rate of the fiber and lens system determine the energy-saving rate. In this case, the authors might want to include the performance evaluation of the optics and probably a couple of sentences to discuss how to further improve the efficiencies.
(2) In Section 2.3, Lighting Demand Algorithm, the authors listed the equations for calculating the required luminance and the corresponding power adjustment. Several constant parameters are involved, such as κ, W, ω, and η. It would be helpful to provide the specific values of these parameters to validate the whole calculation.
(3) In Figure 12, the axis labels were missing.
Author Response
Point 1: It seems that the coupling efficiency and transmission rate of the fiber and lens system determine the energy-saving rate. In this case, the authors might want to include the performance evaluation of the optics and probably a couple of sentences to discuss how to further improve the efficiencies.
Response 1:
Thank you for your comment. In this system of DSFO, the coupling efficiency from the lens combination for collecting sunlight to the optical fiber cable is the key to determine the overall energy-saving rate. In this study, the free surface Fresnel lens is used to reduce the size of the focused spot, and the six core coupled optical fiber cable is used to improve the coupling efficiency. Next, it is planned to optimize the coupling mode through the design of the optical cone coupling head. So as to further improve the efficiency and reduce the system cost. And improve the popularization of this technology. This discussion has been added to the research outlook of the conclusion.
Point 2: In Section 2.3, Lighting Demand Algorithm, the authors listed the equations for calculating the required luminance and the corresponding power adjustment. Several constant parameters are involved, such as κ, W, ω, and η. It would be helpful to provide the specific values of these parameters to validate the whole calculation.
Response 2:
Thank you for your comment.
is the luminance/illuminance conversion factor, usually 15 lx/(cd/m2); denotes the road width of the corresponding lighting segment, The width of the two lane pavement is 10.4 m in combination with the roadside and maintenance lane.
is two for a symmetrical arrangement and one for staggered, midline, and central lateral single light strips, the system adopts symmetrical arrangement mode, then ω is 2.
represents the utilization of lamps and lanterns coefficients, and for LED lighting lamps η is usually 0.8.
Point 3: In Figure 12, the axis labels were missing.
Response 3:
We thank you for your comment. We have added the axis labels in figure12 (now is figure 14). Such additions can be identified with red fonts.
Author Response File: Author Response.pdf
Reviewer 3 Report
Tunnel lighting design is critical in traffic safety. In this manuscript, the authors proposed a tunnel lighting design based on the usage of daylight. Compare with traditional electrical lighting, their lighting design shows increased average luminance, luminance uniformity, and reduced energy consumption. In my view, this manuscript is useful and I would recommend it for publication in Sustainability after minor revision.
1. Looks like all the symbols and equations are not of publishable quality, the authors should correct them and also mark the number (1,2,3…) for each equation.
2. In Figure 8, the authors should mark the sunlight and LED illumination areas respectively.
3. In Figure 9, how did the authors get the data for luminance requirements, and why it becomes maximum at around 1 pm? The authors should talk in more detail about this.
Author Response
Point 1: Looks like all the symbols and equations are not of publishable quality, the authors should correct them and also mark the number (1,2,3…) for each equation.
Response 1:
We thank you for your comment. We have re-edited formula 1-3 in the manuscript. Such additions can be identified with red fonts.
Point 2: In Figure 8, the authors should mark the sunlight and LED illumination areas respectively.
Response 2:
We thank you for your comment. We have labeled Figure 8 (now is figure 10) in the manuscript. Such additions can be identified with red fonts.
Point 3: In Figure 9, how did the authors get the data for luminance requirements, and why it becomes maximum at around 1 pm? The authors should talk in more detail about this.
Response 3:
We thank you for your comment.
During the test, the system analyzes the luminance required by the test area according to the real-time monitored luminance outside the tunnel automatically. On the premise that the DSFO works, the intelligent control system adjusts the output power of the electrical lighting automatically so that the light intensity in the test area always meets the lighting requirements. The luminance of the test area is measured every hour and the current output power of the electrical lighting is recorded, as shown in Table 1. The detail is shown in the test process of 3.1 and 3.2.1.
The test shows that at 1 p.m., the required luminance and actual luminance of the test area reach the maximum. At this time, the external solar intensity is the maximum, and the light in the tunnel is contributed by solar lighting. Therefore, although the lighting demand is the highest at this time, the actual electrical lighting power is the lowest.
Author Response File: Author Response.pdf
