Analysis on High-Power Seaport LED Luminaire with Uniform Light Distribution Based on Optimized Lens and Heatsink

In the case of light-emitting diode (LED) seaport luminaires, they should be designed in consideration of glare, average illuminance, and overall uniformity. Although it is possible to implement light distribution through auxiliary devices such as reflectors, it means increasing the weight and size of the luminaire, which reduces the feasibility. Considering the special environment of seaport luminaires, which are installed at a height of 30 m or more, it is necessary to reduce the weight of the device, facilitate replacement, and secure a light source with a long life. In this paper, an optimized lens design was investigated to provide uniform light distribution to meet the requirement in the seaport lighting application. Four types of lens were designed and fabricated to verify the uniform light distribution requirement for the seaport lighting application. Using numerical analysis, we optimized the lens that provides the required minimum overall uniformity for the seaport lighting application. A theoretical analysis for the heatsink structure and shape were conducted to reduce the heat from the high-power LED light sources up to 250 W. As a result of these analyses on the heat dissipation characteristics of the high-power LED light source used in the LED seaport luminaire, the heatsink with hexagonal-shape fins shows the best heat dissipation effect. Finally, a prototype LED seaport luminaire with an optimized lens and heat sink was fabricated and tested in a real seaport environment. The light distribution characteristics of this prototype LED seaport luminaire were compared with a commercial high-pressure sodium luminaire and metal halide luminaire.


Introduction
Recently, conventional lighting sources for general lighting applications have been replaced quickly by LED-based light sources. LED-based light sources have advantages to the conventional ones in terms of guaranteed longer life, lower power consumption, higher brightness, and less harmfulness for the environment [1][2][3][4]. However, conventional lighting sources are still mainstream in the area of special lighting applications such as airports and seaports, because these special lighting applications require additional characteristics or special features of more uniform light distribution or higher lighting system reliability, and so on [5][6][7][8][9].
A seaport luminaire shall provide proper illumination to guide ships into port and to support workers in the port to maintain a high level of safety and visibility [10][11][12]. In the case of a conventional seaport luminaire, based on high-intensity discharge (HID) technology such as metal halide and high-pressure sodium lamps, due to glare, the eyestrain of port workers and navigators is at a considerable level [13]. As a result, safety accidents and other work efficiency deterioration are concerns.
In order to improve this kind of situation, efforts are being made to solve the problem by installing reflectors and beam-blocking brackets in the luminaire. However, these kinds of solutions reduce the efficiency of the light source and subsequently increase the volume, weight, and price of the luminaire, too. The luminous flux of LED elements is constantly increasing, and precise light distribution control by optimal lens design is required for desired lighting performance even in lighting products using LEDs [14][15][16][17].
The general radial light distribution curve induces the disability or discomfort of workers or pedestrians due to glare and uneven light distribution. It is possible to suppress glare and optical illusions through the realization of an optimal asymmetric light distribution with a high-power LED light source [18]. However, upon implementing a high-power LED light source, the heat dissipation problem of the corresponding lighting fixture is being raised as a key point, as it is inevitable to replace the LED lighting that replaces it with a conventional 500 W class luminaire in the seaport.
In other words, as the output of the LED increases, the amount of heat generated increases, which affects the life and reliability of the LED [19][20][21][22][23]. Therefore, the heat generated from the LED chip is effectively removed using the metal heatsink to extend the life of the LED chip and increase the light efficiency. Thus, it is necessary to develop a lightweight and optimized high heat-dissipating structure for the seaport LED luminaire. In heat dissipation, it is necessary to implement optimal heat dissipation characteristics by appropriately utilizing the most effective conduction and convection. The key to the heat dissipation design of high-power LED port luminaires should be light weight, convenient maintenance, and no reduction in product life and light efficacy by heat dissipation.
In this paper, we intend to provide the appropriate light distribution characteristics required in a seaport through optimal lens design, and to solve the heat dissipation problem caused by the use of a high-power light source through heat sink optimization. This paper is organized as follows. In Section 2, theoretical analysis and fabrication of optimized optical lens and heatsink for a high-power LED light source will be shown. Then, the fabrication of a seaport luminaire using an optimized lens and heatsink will be followed. In Section 3, theoretical analysis of prototype LED and conventional HID luminaires in seaport application will be described. Actual measurement results of an LED and conventional HID seaport luminaires in seaport installation will be analyzed. Then, discussion on the results of comparing an LED with HID seaport luminaires will be followed in Section 4. Finally, the conclusion of this paper will be presented in Section 5.

Theorotical Analysis and Fabrication of Optimized Optical Lens
To investigate the optimal lens design for the seaport luminaire, the near field optical characteristics of a high-power LED PKG were analyzed. In the measurement, as shown in Figure 1a, Lumileds's Luxeon M LED PKG with 5 W power was used at the distance of 6 mm [24]. The viewing angle and luminous distribution curve of this LED PKG are shown in Figure 1b,c, respectively.
Based on the viewing angle data of the LED PKG, various types of optical lens were designed using LightTools software, as shown in Figure 2a. After theoretical analysis of the light distribution of the LED PKG with an optical lens, four types of lens were selected as candidates for the seaport light source. According to the design of each lens, four types of optical lens were fabricated using a high-speed precision processing machine with PowerMill software, and then, the surface of the lens was polished for high transmittance, as shown in Figure 2b.
Then, the real light distribution data of an LED PKG with an optical lens was measured by a gonio-photometer, as shown in Figure 2c. To verify the feasibility of seaport lighting application, light distribution was simulated using Relux software considering the requirements of seaport lighting application-for example, illuminated area, height of luminaire installation, and required overall uniformity. These boundaries and input conditions used in the simulation are listed in Table 1. The dimensions of the illuminated area are about 150 m by 150 m, as shown in Table 1. Figure 2d shows the simulated result of light distribution, and the expected overall uniformity is about 0.53. Overall uniformity is a measure of how evenly lit the road surface is, and it is calculated by dividing the minimum value of illuminance by the average illuminance [25].
As the required minimum overall uniformity for the seaport lighting application was 0.7, three other types of lens were also investigated to meet the overall uniformity of 0.7.    Figure 3 shows the simulation results of light distribution for four types of lens: A, B, C, and D. Among these four lens types, the light distribution with lens type D provides the best overall uniformity characteristics, as shown in Figure 3d.  Table 1 were used for the simulation of light distribution).
The simulated overall uniformity for each of the four types of lens is summarized in Table 2, and the overall uniformity is 0.48 for lens type A, 0.53 for type B, 0.45 for type C, and 0.73 for lens type D, respectively. It means that only the type D lens meets the minimum overall uniformity requirement of 0.7. Thus, the type of optical lens was fixed as type D.

Theorotical Analysis and Fabrication of Heatsink for High-Power LED Module
The LED module was designed for rated power of 250 W with 48 LED PKGs (4 LED PKGs in serial × 12 LED PKGs in parallel). The operating voltage and current for each LED PKG is 11.7 V and 400 mA, respectively. In order to effectively dissipate the heat generated from the LED chip, the LED is attached to the heat dissipation pattern on the upper side of the PCB with vertical via hole that reduces the heat primarily, and the vertical via hole is in contact with the heat dissipation coating layer at the bottom of the PCB. It is designed so that heat is secondarily conducted to the lower surface, which is close to the aluminum die-casting body with a high heat dissipation coefficient [26]. The thermal characteristics of heatsink were investigated with Solidworks flow software, as shown in Figure 4. A total of four types of heatsink (type A with vertical fin, type B with horizontal fin, type C with triangle fin, and type D with hexagonal fin) were analyzed, and the results are summarized in Table 3. In the simulation, the total amount of fins for type C and D was 118. As a result of these numerical analyses, the heatsink type D with a hexagonal fin shows the best thermal characteristics of 58.4 • C at the top of the heatsink, and this means an improvement of 6.8 K in thermal dissipation performance compared to that of type A. To measure the real thermal characteristics, four LED modules were fabricated with each heatsink type A, B, C, and D, respectively. The 3D dimension of each heatsink was 565 mm × 185 mm × 81 mm. Five thermocouples (from point 1 to point 3: near the LED PKGs top side of the heatsink, point 4 and 5: on the bottom of the heatsink) were attached to monitor the temperature of each heatsink, as shown in Figure 5.
The results of temperature measurement are summarized in Table 4, and as expected from the numerical analysis, heatsink type D shows the best thermal characteristics of 48.6 • C at point 5. The temperature difference between type D (best case) and type A (worst case) is 7.1 K at the bottom of the heatsink (position 5), and these results are very similar to those of the simulated data temperature difference of 6.8 K at the same position, as shown in Table 3.

Fabrication of Seaport Luminaire
The prototype of the seaport luminaire with a rated power of 500 W consists of two LED modules with an optimized lens and heatsink (i.e., lens type of D and heatsink type D), as shown in Figure 6a,b. The total lighting output of this luminaire was 59,162 lm with an input power of 493 W, which means that the luminous efficacy of this luminaire is about 120 lm/W. To verity the feasibility of this seaport luminaire, the asymmetric characteristics of light distribution were measured using a gonio-photometer, as shown in Figure 6c. Then, light distribution was simulated using Relux software considering 150 m × 150 m of the illuminated area, as shown in Figure 6d. The results of simulation show the calculated average illuminance of 92.0 lx, minimum illuminance of 53.3 lx, and thus, overall uniformity of 0.71, which is a value that meets the required overall uniformity of 0.70 in seaport lighting application.

Therotical Analysis of LED and Conventional HID Luminaires in Seaport Application
To verify the feasibility of the developed prototype LED seaport luminaire in seaport lighting application, the light distribution characteristics of the fabricated prototype LED seaport luminaire with conventional HID seaport luminaires were analyzed using Relux software [27,28]. In this analysis, for the conventional HID luminaires, a metal halide luminaire with a rated power of 1000 W and a high-pressure sodium luminaire with a rated power of 1000 W were considered, even though the rated power of the prototype of the LED luminaire is 500 W. In the simulation, 48 luminaires for the single high mask at each corner (192 luminaries in total) were considered for each type of luminaire. The simulation results of light distribution for each type of luminaire are shown in Figure 7. Among these three kinds of luminaire, it shows uniform optical distribution characteristics in the order of the fabricated prototype LED luminaire, the commercial high-pressure sodium luminaire, and the metal halide luminaire. Based on these theoretical analyses, the overall uniformity for three kinds of luminaires was derived as summarized in Table 5. Only LED luminaires satisfied the overall uniformity of 0.7 or more required by seaport lighting application, even though the metal halide luminaire shows the largest average illuminance.

Actual Measurements of LED Seaport Luminaire and Conventional HID Seaport Luminaires in Seaport Installation
To measure the actual optical performances of the developed prototype LED seaport luminaire, we set up a testbed at a real seaport with an installation of an LED luminaire and an HID luminaire. At the seaport area, a total of six sections with 56 measurements points were selected, as shown in Figure 8a, and illuminance sensors were installed at every one of the 56 measurement points to get the illuminance data, as shown in Figure 8b.
The measured illuminance values for each measurement point were presented in Figure 8c for HID luminaires (1000 W HID luminaire × 12ea) and Figure 8d for LED luminaires (500 W LED luminaire × 12ea). Compared to the HID luminaire's case, the measured illuminance data of the LED luminaire show more uniformly distributed values at Sections 4-6. The measured average illuminance of the HID luminaire was about 54 lx, whereas the simulated value was 65 lx. In the case of the LED luminaire, the measured average illuminance was about 80 lx, whereas the simulated value was 92 lx. Thus, there is a 10 lx difference between the simulation and actual measurement. Simulated and measured values for average illuminance and overall uniformity are summarized in Table 6.

Discussion
The simulated result in Section 3.1 and actual measured data in Section 3.2 show that the LED luminaire has more uniform light distribution due to using the optimized lens described in Section 2.1. Moreover, the LED luminaire has a higher luminous efficacy of 124 lm/W compared than that of the commercial HID (metal halide) luminaire, which is about 70 lm/W with the optimized heatsink, as described in Section 2.2. The required characteristics of seaport lighting application were investigated, and the analyzed features of the LED and commercial HID (metal halide) luminaire were summarized in Table 7. Due to the high luminous efficacy of LED luminaires, an equivalent light output could be achieved with only half the power of the HID (metal halide) luminaires. Thus, the rated power of a 500 W LED luminaire could replace the rated power of a 1000 W HID (metal halide) luminaire. Normally, the lighting tower has 48 luminaires; thus, it means with LED luminaires, 24,000 W of energy could be saved. Since lighting consumes a large portion of electricity, an LED seaport lighting system can be integrated into the port energy management system due to the capability of controlling of LED-based light source [29,30]. The seaport luminaire shall be installed with a height of more than 30 m; thus, the longer lifetime is one of the critical factors in the seaport lighting application, because a longer lifetime means less maintenance cost and activity. The life of LED luminaires is ten times longer than that of HID (metal halide) luminaires, as shown in Table 7. Summarizing the above simulated and measured results, it can be seen that LED luminaires with more uniform light distribution, higher luminous efficacy, and less power consumption are more suitable for port lighting than conventional HID (metal halide) luminaires.

Conclusions
In this paper, an optimal lens and heatsink design has been analyzed both through theoretical investigation and experiments to provide the appropriate light distribution characteristics required in seaport lighting application. Then, prototypes of seaport LED luminaires were fabricated using the optimized lens and heatsink. Finally, actual measurements results of LED and conventional HID seaport luminaires in a seaport installation were showed and discussed.
In case of lens optimization, in order to develop a lens that provides a uniform light distribution, four types of lens were theoretically analyzed and their actual light distribution was measured. As a result, the type D lens showed an overall uniformity of 0.73, whereas the required overall uniformity is about 0.7. In optimization of heatsink, the thermal characteristics of a heatsink with various shapes and structures have been investigated. The temperature difference between type D with a hexagonal-shaped fin (best case) and type A with a vertical fin (worst case) was 7.1 K at the bottom of the heatsink, and these results are very similar to those of simulated cases.
To verify the feasibility of the developed prototype LED seaport luminaire in seaport lighting application, the light distribution characteristics of the fabricated prototype LED seaport luminaire with conventional HID seaport luminaires were theoretically analyzed. Then, actual measurements using the testbed with a total of six sections with 56 measurements points were conducted. The LED seaport luminaire shows more uniformly distributed values such as an overall uniformity of 0.5 (in case of simulation: 0.72) and average illuminance of 80 lx (in case of simulation: 92 lx). Moreover, the LED luminaire has a higher luminous efficacy of 124 lm/W compared with that of the commercial HID (metal halide) luminaire of about 70 lm/W. The required characteristics of seaport lighting application were investigated, and the analyzed features of the LED and commercial HID (metal halide) luminaire were described in the discussion section. Summarizing the above simulated and measured results, it can be seen that LED luminaires with more uniform light distribution, higher luminous efficacy, and less power consumption are more suitable for port lighting than conventional HID (metal halide) luminaires.
In this paper, the seaport with a horizontal layout was considered and analyzed. Thus, the seaport with a vertical layout, which has long single block perpendicular to the shore, may require different light distribution characteristics [31,32]. However, a similar approach to the method used in this paper will be helpful in that case, also. In the future, additional research is needed to improve and to secure environmental resistance according to environmental conditions such as salt water.

Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author.

Conflicts of Interest:
The authors declare no conflict of interest.