Tunnel Lighting Research Articles

(Invited) Isolating an Individual Ion Emitter and Light-Induced Tunneling Upconversion

This talk will review two recent discoveries made in my group. Single Photon Emitters: Intrigued by the promise of single-photon quantum technologies, many have studied the properties of single ion defect emitters, particularly lanthanides in a crystal matrix (including praseodymium, cerium, and erbium). I will report on a way of reliably isolating individual erbium ion emitters in nanocrystals with the potential for 100% individual emitter yield in post-selection. We used a nanoplasmonic (metal nanostructure) aperture optical tweezer to reliably isolate individual erbium ion emitters in individually trapped NaYF4 nanocrystals. The nanoplasmonic aperture solved two major problems: (1) it enhanced the emission rate so that single ions could be detected reliably in a short time, and (2) it isolated the single Er containing nanocrystal from the other nanocrystals in solution. This new demonstration follows our recently published work showing 400× increased emission using the nanoapertures. Light-Induced Upconversion Emission: Upconverted light from nanostructured metal surfaces can be produced by harmonic generation and multi-photon luminescence; however, these are very weak processes and require extremely high field intensities to produce a measurable signal. Here we report on bright emission, 5 orders of magnitude greater than harmonic generation, that can be seen from metal tunnel junctions due to light-induced inelastic tunneling. Like inelastic tunneling light emission, which was recently reported to have 2% conversion efficiency per tunneling event, the emission wavelength recorded varies with the local electric field applied; however, here the field is from a 1560 nm femtosecond pulsed laser source. Finite-difference time-domain simulations of the experimental conditions show the local field is sufficient to generate tunneling-based inelastic light emission in the visible regime. This phenomenon is promising for producing ultrafast upconverted light emission with higher efficiency than conventional nonlinear processes.

Dynamic luminance tuning method for tunnel lighting based on data mining of real-time traffic flow

Tunnel lighting constitutes one of the major expenses incurred in transportation lighting, and hence substantial research has been conducted to improve the efficiency of lighting and thus to minimize operating costs. This paper investigates an intelligent method for adjusting tunnel lighting with dynamic control based on data mining of traffic flow distribution, traffic composition, and vehicle speed distribution. Field monitoring data of traffic flow in five real expressway tunnels, which are in HeDa expressway, Jilin Province, China, was used in the analysis. The K-MEANS clustering algorithm was used to group (or cluster) the distribution of daily traffic volume into six-time periods, in which the traffic volume includes two peak periods (8:01–11:23 and 14:31–19:01). A dynamic luminance regulation method is proposed that distinguishes operational strategies under different time periods. Furthermore, the impact of tunnel length and traffic flow on the effect of energy-saving and system sustainability of the proposed method was assessed. The results show that when using the proposed method, the energy-savings in tunnel lighting could be between about 50% and 60% for a daily traffic volume between 750 and 2500 vehicles. The results also show that the switching frequency of the lighting system is significantly reduced, which would significantly enhance the sustainability of the lighting system.

Design of Counter Beam Tunnel Lights for CIE 88 : 2004 Regulation in Threshold Zone

To enhance driving safety, a counter beam light is proposed to meet CIE (International Commission on Illumination) specifications for tunnel lighting. The proposed new counter beam light (CBL) acts as a qualified counter beam light to help tunnel road lighting meet the CIE 88 : 2004 regulation standard in the threshold zone in both simulation and in practice. Through appropriate arrangements of the counter beam light and conventional fluorescent lights on the tunnel ceiling, we demonstrate that road tunnel lighting meeting CIE 88 : 2004 standards can be accomplished. Based on LiteStar four-dimensional simulation, the source file created through the measurement of the proposed CBL prototype achieved an average road surface brightness of 121 cd/m2, which is greater than the minimum regulation level of 105 cd/m2, a brightness uniformity of 0.88 (minimum regulation level of 0.4), longitudinal brightness uniformity of 0.98 (minimum regulation level of 0.6), a glare factor of 4.41% (maximum level of 15%), and a contrast revealing coefficient of 1.08, which is above the 0.6 minimum level in the threshold zone.

The Impact of Color Rendering on Perception Luminance in Interior Zone of Tunnel Considering Low Visibility

LED lights are widely used in highways and tunnels because of their long life, low light attenuation in recent years. The influence of color rendering (CRI) on lighting safety has attracted people's attention as the increase in demand. In this paper, the influence of different CRI on perception luminance of human eyes under different fog transmittance and different luminance was calculated and analyzed. A calculation model of human eye perception luminance considering mesopic vision and fog concentration was proposed. An experiment was conducted by observing different colored targets in a fog chamber. The results showed that yellow targets and high CRI can provide higher perception luminance and the latter is recommended for tunnel lighting in interior zone.

The Impact of LED Color Rendering on the Dark Adaptation of Human Eyes at Tunnel Entrances.

The dark adaptation of drivers’ eyes at a tunnel entrance seriously affects traffic safety. This can be improved by the design of tunnel lighting. Light-Emitting Diode (LEDs) have been applied as a new type of luminaire in tunnel lighting in recent years, but at present, there are few studies on the influence of color rendering of LEDs on tunnel traffic safety, and there is no explicit indicator for the selection of appropriate color rendering parameters in tunnel lighting specifications, which has aroused researchers’ concern. In this article, several new color rendering evaluation indexes were compared, and as a result, it is considered that CRI2012 (a color difference-based color rendering index) is more suitable for evaluating the color rendering of LEDs used at tunnel entrances. The dark adaptation phenomenon was simulated in the laboratory. Four CRI2012s, three color temperatures and eight colored targets were used in the experiments. The results showed that yellow, silver and white can provide shorter reaction times, while red and brown lead to longer reaction times, which can provide a reference for the design of road and warning signs at tunnel entrances. The effect of target color on reaction time was greater than that of color rendering. Under most target colors, the higher the CRI2012, the shorter the reaction time. When designing the color rendering of the LEDs at a tunnel entrance, the value should thus be as large as possible (close to 100), and a lower color temperature value (about 2800 K) should be selected. This paper provides technical support for tunnel lighting design and a reference for tunnel lighting specifications, which is of significance to improve driving safety and avoid traffic accidents in highway tunnels.

Design of multi-channel data collector for highway tunnel lighting based on STM32 and Modbus protocol

This paper proposes a multi-channel data collector based on STM32 and Modbus protocol for highway tunnel lighting system. In terms of hardware, a STM32 microcontroller is designed as the main controller, and BH1750 sensor and DHT11 sensor are chosen to measure illuminance and temperature-humidity, respectively. In terms of software, the measured illuminance and temperature-humidity are read by I²C and single bus, respectively. Based on the RTU working mode of Modbus protocol, STM32 successfully transmits the collected data to host computer, and realizes the real-time collection and uploads of highway tunnel environmental parameters. Furthermore, the proposed data collector has operated stably in a tunnel lighting energy-saving system for nearly two years. The experimental results show that the proposed multi-channel data collector can sense tunnel environment accurately and communicate with upper computer reliably, and has good engineering application value.

In situ observation of slow and tunnelling light at the cutoff wavelength of an optical fiber.

Slow waves and tunneling waves can meet at the cutoff wavelengths and/or the transmission band edges of optical and quantum mechanical waveguides. The experimental investigation of this phenomenon, previously performed using various optical microstructures, is challenged by fabrication imperfections and material losses. Here, we demonstrate this phenomenon in situ for whispering gallery modes slowly propagating along a standard optical fiber, which possesses a record uniformity and exceptionally small transmission losses. The slow axial propagation dramatically increases the longitudinal wavelength of light and allows us to measure nanosecond-long tunneling times along tunable potential barriers having the width of hundreds of micrometers. This demonstration paves a simple and versatile way to investigate and employ the interplaying slow and tunneling light.

Study on Luminance in the Threshold Zone of Highway Tunnel

Currently, highway tunnel development is on the upswing. As an important guarantee for traffic safety in highway tunnel, tunnel lighting has a short history of research. Since the 1960s when tunnel lighting began to become a subject of research, it was gradually and profoundly realized that lighting at the tunnel threshold zone was the focus of the entire tunnel lighting. This paper provides a review on past research into tunnel lighting and findings, and then introduces the latest theory and calculation methods regarding the luminance in the threshold zone of highway tunnel with a view to giving some valuable reference for engineering practice.

Evaluation Techniques for Traffic Safety of Operating Highway Tunnels

With the consideration of frequent occurrence of traffic accidents on operating highway tunnels, the advancement of safety evaluation for highway tunnels in domestic and abroad are systematically summarized. Through the comprehensive analysis of infrastructure factors influencing on traffic safety of highway tunnels, safety checklists focusing on tunnel horizontal and vertical alignment, tunnel portal situation, pavement condition, ventilation and lighting facilities, traffic safety facilities are provided in qualitatively evaluating operating highway tunnels. Based on the concept of risk, risk assessment indices oriented in infrastructure factors, environmental factors and management factors for operation safety of expressway tunnels and standard highway tunnels are put forward. Quantitative evaluation methods based on indices architecture and the corresponding classification criteria for operation safety risk of tunnels are developed.

Research on Safety Evaluation Method of Tunnel Visual Environment

Starting from the driver’s visual features, safety evaluation indicators and methods of tunnel visual environment are proposed against the tunnel visual environmental characteristics, providing scientific guidance for special lighting environment in the tunnel to increase visual stimulation, transforming previous subjective evaluation into quantitative evaluation and thus improving tunnel traffic safety level effectively. The method can also be extended to the safety evaluation of other scenarios such as tunnel decoration and light color temperature.

The Correlation Research on Reflection Characteristics of Road Tunnel’s Internal Surface & Lighting Quality

The internal wall and road surface of tunnel form the background of roadblock or vehicle together, and have a significant influence on the safety and comfort of tunnel lighting. In this paper, the optical simulation program is adopted to analyze the correlation between the reflectivity of tunnel wall and such illumination indexes as luminance and illuminance of road surface inside a tunnel, as well as the visibility of small target etc. It shows from the study that: (1) The reflectivity of wall on the luminance gain level of road surface is closely related to the luminous intensity distribution of lamps. (2) Under the circumstance that the luminous intensity distribution of lamps is consistent, the linear relations basically exist among the reflectivity of wall, the illuminance and luminance of road surface and the luminance of wall, while the maximum growth slopes are 11.29, 0.45 and 11.50 respectively. (3) The field of vision of driver can be significantly improved by a higher reflectivity of wall. (4) Compared with the three illumination modes, the visibility of small target under the pro-beam lighting is highest (the minimum visibility is 10, and the highest visibility can reach 11.6), while the visibility of small target under the counter-beam lighting is the second-highest and the visibility of small target under the symmetric lighting is most non-obvious.

Impact of LED Color Temperatures on Perception Luminance in the Interior Zone of a Tunnel considering Fog Transmittance

LEDs are widely applied in highways and tunnels for their long life, low light attenuation, and being environment friendly in recent years. The influence of correlated color temperature (CCT) of LED on lighting safety has attracted people’s attention as the demand increased. In this paper, a calculation model of perception luminance of human eye considering mesopic vision and fog concentration was proposed. The influence of different CCTs on perception luminance of human eye under different levels of fog concentration and luminance was calculated and analyzed. The CCT of LED employed in the interior zone of a tunnel was selected based on the highest perception luminance in mesopic vision. Seven kinds of LEDs with different CCTs (3000–6500K) were applied in the experimental system with adjustable fog concentrations. The results showed that the main factors affecting visual perception are luminance and fog concentration. Higher luminance or lower fog concentration provides drivers with higher perception luminance. In contrast, although CCT has a less effect on perception luminance, LEDs with higher CCT (about 6500K) can provide higher perception luminance considering fog in mesopic vision. This paper provides technical support for tunnel lighting and guaranteeing traffic safety.

Development of DC Power Supply Tunnel Lighting System

Development of DC Power Supply Tunnel Lighting System

Study on Energy Saving Technology of Night-time Illumination of Expressway Tunnel

With the continuous expansion of the scale and number of highway tunnels in China, the power consumption of highway tunnel lighting has gradually become a huge amount for operating units. How to reduce the power consumption of lighting for highway tunnels has become an important issue for operating units. However, energy saving does not mean less or no lights, the premise must be to ensure the safety and comfort of driving in the tunnel. In this study, based on the light environment characteristics of the tunnel at night, the visual resolution level of the target obstacle in front of the road is judged by the human eye ’s saccade time, and whether the reduction of road lighting brightness under the effect of the headlights will affect the driver ’s visual resolution level. The results show that the turning on of the car's high beam lights has a certain effect on the driver's visual perception ability; when the average brightness of the road surface is 1.0cd/m², the tester's saccade and fixation time on the target obstacle are less than 0.5cd/m², But the driver has no significant difference in the resolution of the target obstacles under these two brightness levels; when the brightness of the road surface is 0.5 cd/m², the driver still has confidence in the situation ahead; it is recommended that the entrance and exit have a certain distance The tunnel brightness can be adjusted to 0.5cd/m².

The hybrid lighting system with natural light and LED for tunnel lighting

The traditional tunnel lighting has the problem of poor lighting environment and huge energy consumption. This study uses natural light and LED as the light source to design two different lenses. When the natural light is sufficient, the natural light illumination system is used in the threshold zone and the exit zone, give tunnel lighting to reduce the number of LEDs used. When the natural light is insufficient, the sensor will detect the natural light level of the collimator exit to control the LED to compensate for the light or to illuminate the tunnel alone. In the two designs, the linear Fresnel lens is established by the Fresnel structure, and the free-form asymmetric lens of the LED is established by the catadioptric method. Finally, the model of the Hsueh-Shan tunnel was established by DIALux, and the two lenses were used simultaneously for mixed illumination to simulate average luminance, total uniformity, and longitudinal uniformity. The lens design reduces the influence of glare, and the design of the lamp spacing reduces the zebra pattern on the road surface. Combined with natural light and artificial light source, the tunnel light does not need to be 24 h of operation can save energy.

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

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.

Charge Carrier Injection Electroluminescence with CO-Functionalized Tips on Single Molecular Emitters.

We investigate electroluminescence of single molecular emitters on NaCl on Ag(111) and Au(111) with submolecular resolution in a low-temperature scanning probe microscope with tunneling current, atomic force, and light detection capabilities. The role of the tip state is studied in the photon maps of a prototypical emitter, zinc phthalocyanine (ZnPc), using metal and CO-metal tips. CO-functionalization is found to have an impact on the resolution and contrast of the photon maps due to the localized overlap of the p-orbitals on the tip with the molecular orbitals of the emitter. The possibility of using the same CO-functionalized tip for tip-enhanced photon detection and high resolution atomic force is demonstrated. We study the electroluminescence of ZnPc, induced by charge carrier injection at sufficiently high bias voltages. We propose that the distinct level alignment of the ZnPc frontier orbitals with the Au(111) and Ag(111) Fermi levels governs the primary excitation mechanisms as the injection of electrons and holes from the tip into the molecule, respectively. These findings put forward the importance of the tip status in the photon maps and contribute to a better understanding of the photophysics of organic molecules on surfaces.

Controlling light tunneling by adiabatic passage in two modulated nonlinear waveguides

We theoretically investigate light propagation in two coupled nonlinear waveguides with a certain static propagation constant detuning between two waveguides and with the linear refractive index modulated along the propagation direction. By slowly varying the amplitude of modulation, we steer the light to the desired output waveguide when equal amounts of lights are launched into each waveguide. We reveal that depending on the sign of the static propagation constant mismatch (detuning) between two waveguides, the launched light can be completely switched to either of waveguides. Additionally, we numerically examine the performances of light switching for general inputs and modulation amplitudes, and show that the localization of output light is robust against small to moderate variations in the final modulation amplitude, phase difference and intensity distribution of input field between two waveguides. More importantly, according to the principle of the proposed scheme, we are capable of steering the output light to the targeted waveguide at extremely low input power. In theory, our findings can be explained qualitatively by means of adiabatic navigation of the so-called nonlinear Floquet states.

Meta-interface enhanced light tunneling effect and related electromagnetic diode action

A subwavelength electromagnetic diode scheme is proposed that includes a light tunneling heterostructure with an embedded Fano-like highly dispersive metainterface. Due to the presence of the Fano-like metainterface, the transmission properties of the light tunneling heterostructure, including its Q-factor and electromagnetic field, can be optimized for a better diode behavior. The concept is demonstrated based on a microstrip transmission line system with asymmetric absorption and nonlinear medium inclusion. This configuration is found to generate an extremely high transmission contrast of up to 18.5 dB at a working frequency of 725 MHz. A further advantage of the configuration is that, with an input power intensity of only 8.2 dBm, the unidirectional transmission can still exceed −30 dB. These features may be useful in the design of integrated ultralow-power nonlinear devices.

Experimental study on energy-saving of highway tunnel lighting with symmetric lamp distribution

In order to study the energy-saving of highway tunnel lighting experimentally with low cost, a similar tunnel model was designed and used for the lighting experiment. Yanlieshan highway tunnel was selected as the study object. On the basis of the tunnel structure sizes (TSS) and the selected LED lamps, the optimized symmetric lamp installation parameters (OSLIPs) for energy-saving were obtained with the lighting parameters optimization model (LPOM) on symmetric lamp distribution (SLD) from reference. Based on the TSS and the OSLIPs, a simulation experiment of the tunnel lighting was accomplished with DIALux. A similar tunnel model was designed and built according to the TSS and similarity theory, and a tunnel model lighting experiment with SLD was carried out. The road-surface-illuminance (RSI) data of the tunnel model lighting experiment were compared with the simulation experiment results. The comparison of horizontal RSI from the two methods coincide well, which proves the LPOM is correct, the lighting experimental study with similar tunnel model is feasible and the experiment method in this study is valid.