Introduction
LED fish-attracting lamps have been studied for use with common squid or hairtail since 2006 in Korea. Current methods execute an equipped site-adaptive test in squid or hairtail jigging fisheries using a fishing boat. The catch amount of with coupling LED and MH lights was measured to be similar to or greater that 80% of that of a similar class fishing boat with only MH lights (Bae et al., 2009) An efficient product that was both structurally stable and which yielded good fishery performance was developed, and a test comparing 24 metal-halide fish-attracting lamps (24×3 kW = 72 kW) with LED lamps (216×0.7 kW = 151 kW) showed that, even though the catch with LEDs was 90% of that using only metal-halide lamps, energy consumption was reduced by 15-20% (An et al., 2012). The increase in domestic LED fish-attracting lamp manufacturers and the variety of products available has led to a decrease in price differences, and market competition for high-power products is increasing. Competitive overproduction, as occurred with metal halides, may result. A technical standard for LED fish-attracting lamp package production is required to ensure reliability and standardization in the industrial design of LED fish-luring lamps to prevent energy overconsumption.
Characterization of LED packages requires assessment of their electrical, optical, and thermal properties. The basic operational principle of an LED package is the conversion of electrical energy to light energy. The electrical characteristics of interest are the operating current (Iop), forward voltage (Vf), resistance current (Ir), surface resistance (Rs), and the PN junction diode (Hwang et al., 2010), a component that is prone to electric overstress (EOS) through a current- driven elemental mechanism. The optical characteristics of interest are light output (W), luminance (lm), light intensity (cd), efficiency (lm/W), chromaticity coordinates, color temperature, color rendering index, and light distribution. The thermal characteristics of interest in an LED package are the junction temperature (Tj), thermal resistance, and package/packaging thermal (mechanical) stress (Narendran and Gu, 2005; Kim et al., 2007; Lu et al., 2009; Cho, 2011). The thermal characteristics play a significant role in the design of LED fish-attracting lamps, as the packaging requires weight and size restrictions compared to other LED packages. Heat release is achieved by using a heat sink, a component that maintains stable thermal equilibrium in the LED package, and which has an efficiency proportional to the surface area; hence weight restrictions complicate the design of an LED package.
In this study, a high-power LED fish-attracting lamp was designed by investigating the thermal characteristics of a 25-W module. A 250-W LED was manufactured, and basic data for fish-attracting lamp development were proposed by examining the design of the high-power LED.
Materials and methods
25-W level LED module
A recently developed high-power LED package, used for general lighting, has been adapted as a 1-W to 3-W chip package for home lighting, street lighting, and flood lighting.
A 2-W, 140-lm/W LED package (15EA) was used to produce a 250-W high-power LED fish-attracting light, and the production method is outlined in Table 1 and Fig. 1. A lens in an integrated cover was applied to each LED chip to improve its distribution characteristics and efficiency. The set-up tilt angle of 30° was designed considering the current power of LED fish-attracting lamps, to reduce unnecessary light consumption.
The containing structure and heat sink were manufactured from processed aluminum. The lens, a high permeability polycarbonate molded part, showed a 92% penetration ratio. A 25-W switching mode power supply (SMPS, BHW-30-12, Zhongshan Boho Optoelectronic Co., China) was used as the power supply, and was designed to operate at 12 V.
The heat radiation structure of two modules was investigated, by performing a heat radiation simulation of one LED module incorporating only a heat sink, and a further module with liquid cooling technology applied, combining a heat sink and heat pipe (Kim et al., 2007; Lu et al., 2009). Experiments on the heat radiation surface area, shape, and exterior elements (wind velocity) were conducted as shown in Fig. 2.Table 2
Importance of LED heat radiation
It is important to process the heat generated by a high-power LED, not only through board manufacturing techniques but also by the design of a small diffusivity component that can remove heat from the LED in high-temperature environments.
An LED can exhibit a change in brightness of more than 30-40% depending on the temperature, and temperature changes in high-power LEDs shorten the life of the product by increasing structural stress (Lee et al., 2010). Thus, a technique and component that actively control the temperature of the LED absorption section are necessary. The temperature can be lowered by increasing the heat-sink surface or by using a flow fan or heat pipe and a liquid cooling technique (Kim et al., 2007). Products with high electricity consumption, such as high-power LEDs, convert 80-85% of electrical power into heat, and the generated heat causes direct stress to the chip, reducing the light output efficiency or mutating the color temperature, and shortening the bulb life. To maintain the luminance and reduce energy consumption, an appropriate drive algorithm and electric circuit design are required. The power consumption can be greatly reduced by using appropriate LED power control techniques. Heat transmission from LED radiation can be broadly divided into that from the LED chip and that from the heat sink (Cho, 2011). The conduction response of the LED chip and accessories is shown in Eq. (1).
Here, ΔT1 is the difference in temperature by stage at the junction temperature (T j), the case temperature (T c), the board temperature (T b), and the heat-sink temperature (T h ). Qcd (W) is the current, ΔT1 is the voltage, R cd is the resistance (K/W), L (m) is the thickness, A is the contact area (m2) and λ(W/m·K ) is the conductive heat transfer coefficient.
The convection response at the LED heat sink is shown in Eq. (2). Here ΔT2 is the temperature difference between the heat-sink temperature (T h ) and the ambient temperature (T a). Eq. (2) shows that R cv(K/W) will vary through natural convection or forced convection, and that the convection response occurs in the heat sink and in the ambient environment. Qcv(W) is the current, ΔT2 is the voltage (K), R cv(K/W) is the resistance, A (m2) is the contact area, and λ(W/m>2·K ) is the convective heat transfer coefficient.
An LED package design that does not consider the thermal characteristics shown in Fig. 3 will overlook important design parameters, such as choice of SMPS and product life (Cho, 2011; Narendran and Gu, 2009). Thermal characteristics can be broadly divided into natural convection considering the influence of gravity only, and forced convection that eliminates heat externally. Forced convection using a fan to discharge internally accumulated heat to the outside is the most effective method of the two; however, this method has the disadvantage that additional design is required to operate the fan, which may have limited durability, and the use of forced convection has been decreasing recently (Hwang et al., 2010). This study simulated heat radiation under the assumption that the external forced convection has a constant flow.
Since the external environment of an LED fish-luring lamp contains many forced convection phenomena, such as wind, during design it is important to consider the structural form and shape of the heat sink as well as the characteristics of the heat transmission mechanism. Forced convection is more effective than the natural convection characteristics of the product. However, a design that considers actual thermal characteristics may overlook the difference in thermal stress when there is no forced convection compared to the effect of forced convection.
250-W fish-luring lamp with 25-W LED module
The most significant design factors for a commercial LED fish-attracting lamp are performance (light efficiency), price, mass producibility, radiation, and resistance to water. Performance and radiation have a close proportional relation; however, price and a mass- producible waterproof design are inversely related. In this study, a 250-W LED fish-attracting lamp was manufactured using researched module data that considered five major factors. The module was tested for thermal characteristics, and the efficacy and performance values of these five factors were used as basic data for high-power LED design.
Results and Discussion
LED module experiment
Each module had a tilt angle of 30°, the same as the installation angle for an actual LED fish-attracting lamp, as shown in Fig. 4. The outer temperature was set to 20°C, and the simulation was conducted under the natural convection conditions of the LED junction temperature: 50-60°C. The thermal characteristics change depending on each module through forced convection (0.5 m/s) as shown in Fig. 5, where the module system level was simulated.
The right hand module (with a heat pipe applied) showed sufficient thermal equilibrium (the heat distribution from the heat starting point to the system end point) at the heat sink, as shown in Fig. 6. The left-hand module (with a heat sink) and the right-hand module exhibited Tj: 97.3°C and Tj: 81.0°C, respectively. Δ T was 77.3°C and 61.0°C , respectively, with a difference of 16.3°C. Therefore, Tj can be set slightly higher such that the difference Δ T = 16.3°C. The high-temperature internal heat is proportional to the heat-sink surface in the module such that thermal exchange occurs only through the heat sink; therefore, the length and thermal resistance increase. On the other hand, the heat-pipe module shows better thermal equilibrium than the heat-sink module because external heat transmission is achieved smoothly, with a smaller heat-sink size.
As shown in Fig. 7, Tj was 83.9°C in the heat-sink module and 65.2°C in the heat-pipe module. Δ T was 63.9°C and 45.2°C in the two modules, respectively, with a difference of 18.6°C. The change in Tj due to forced convection brought about constant quantitative changes in Δ T = 13.4°C and Δ T = 15.8°C, respectively, as compared to natural convection. It can be assumed that when considering an actual LED fish-attracting lamp installation environment, forced convection occurs as a result of continuous wave surges even without effects such as wind. Thus, thermal characteristics owing to forced convection should be considered as essential elements in the development of LED fish-attracting lamps, and standards including this should be prepared.
Fig. 8 shows the flow field as a speed vector field. During the radiation design of the product, the exterior design can be optimized to maintain thermal equilibrium when forced convection occurs by reducing the length of the heat sink when the flow speed is relatively slow, by increasing the surface area of the heat sink, and by considering nearby flow field characteristics when the flow speed is high. Temperature characteristics should approach the product design stable target thermal conditions.
Here, q is the heat flux (J/m2-s) and k is the thermal conductivity (J/mK-s). As in Eq. (4), the specific thermal conductivity has an interaction formula that involves the length and the temperature difference. The standardized interaction formula is proportional to Tj, and Tair. Δ T and the heat sink are important factors in LED module design. Simulation of the two models showed that superior Δ T is achieved in the left-hand heat-pipe model. The temperature difference between the two models was 18°C on average. As a result, Tj = 55-60°C can be set for both the heat-sink and heat-pipe models; thus, the number of LED components per chip can be increased or minimized. However, when considering low-cost mass production, selection of the LED module must be considered, including the use of an expensive heat pipe, endurance, and the complexity of the manufacturing process. There are also other characteristics to consider when managing products that are used in a marine environment.
Radiation simulation and design
As described in earlier research on the thermal characteristics of LED modules, conduction and convection have significant impact on the radiation structure. Design elements that consider conductivity are the selection of materials, the LED board, and the contingent heat resistance between the heat sinks. The conductivity of thermal grease (4.5 W/mK) and aluminum (237 W/m2K) were included in our simulation as heat-sink materials to reduce the contact resistance. In the heat-sink structure with Tj = 55-60°C, the heat-sink area was widened and the location and shape were transformed to allow for both natural and forced convection. The efficiency was found to be 20% higher than that of the former symmetric structure.
The 250-W LED fish-luring lamp designed in this study was designed by predicting efficiency and radiation structure using the 25-W LED module shown in Figs. 9 and 10. The actual Tj is 70°C lower than the simulated Tj of 97.3°C in the LED module. Overall, simulated results were 10-15°C higher than the measured Tj of 55-60°C. Hence, the heat-sink area was increased by more than 30% and the heat-sink shape was optimized in the LED module. Furthermore, this design maintained the thermal reliability using the same lens while being efficient and cost effective.
Measurements of the former 250-W LED module showed an efficacy between 95 lm/W to 86 lm/W, and a luminous efficiency 10% lower. Heat stress was more concentrated on the outside, depending on the location of the LED chip, compared to the independent LED module. It was expected to cause to increase by the roughness of the heat-sink convection structure because of the efficacy and Tj thermal equilibrium. In addition, the decrease in SMPS efficiency was also considered by the output increased. The SMPS was manufactured under the conditions summarized in Table 3.
Performance assessment
Comparing the initial temperature rise near the chip and the former 180-W LED fish-luring lamp shown in Fig. 11, a temperature difference of around 40% was observed compared to the commercial product.
The 180-W LED fish-luring lamp does not have a smooth initial heat release; therefore, more time is required for the thermal stress to reach the target thermal conditions. This was taken into consideration while designing the 250-W LED product, since thermal effects that may affect the performance of such products should be foreseen.
Conclusion
This study provided reliable data for high-power LED lamp development by investigating thermal characteristics and simulating a 25-W LED module. The utility of the 250-W high-power LED fish-luring lamp that was developed was verified. These data may contribute to reduction of losses through repeated development and waste of human resources in the competitive high-power LED lamp market. Although its efficacy was not exactly proportional to the increasing the number of LED modules, there was shown in a similarity of more than 85%. Competitive commercial output of LED fish-attracting lamps has deviated from the initial purpose of reducing the carbon emissions and environmental destruction caused by fossil fuel use, and is instead focused on exterior appearance rather than on the production of reliable and durable products. The development of reliable and standardized products should be the goal of the business environment. Standards for the properties and size of the heat pipe in modular LED packages should be provided to reduce development cost and time.
