Fishermen use light to attract fish to form a large shoal using artificial light source at night or when the weather is cloudy   . Therefore, fishing lamp is the most important equipment used in fishing activities. Examples of widely used fishing lamps include filament lamps, halogen tungsten lamps, metal halide lamps and candela lamps, all of them belonging to thermal light source. Fishing lamps can be categorized into two, that is, overwater fishing lamps and underwater fishing lamps   . Overwater fishing lamps are always suspended near the water surface by hanging them on the rod which is tighten on the boat where they give out light to attract fish, for example candela lamps   . On the other hand underwater fishing lamps are dipped into water for the same purpose, for example Light Emitting Diode (LED) lamps. It has been found that semiconductor lighting technology-LED has advantages of energy saving     . Overwater fishing lamp is suspended near the water surface, and then half of the light is wasted, because the water surface is like the mirror which reflects (sends back) half of the light up in air. While with an underwater fishing lamp, you do not lose any light hence all the light from the lamp spreads underwater and attracts more fish   .
Most fishermen in Tanzania particularly are still using candela lamp to attract fish so that they can capture them using the nets they have. These candela lamps are expensive to run as they consume a lot of energy (kerosene fuel consumption in particular). Since fuel consumption is large, then expenditures (money) becomes very high in buying kerosene fuel (that its price is increasing everyday) to regenerate energy in those lamps. Thus, to solve these problems the research aimed to design underwater fishing lamp which is expected to be more efficient than candela lamps. The device will enable the fishermen to attract more fish which leads to more production. Also it is expected that the price of fish in the market to be reduced because the running cost of the device will be low compared to the running cost of candela lamp.
2. Analysis and Design
In order to design the LED underwater fishing lamp, the following material were required; Two green LEDs (1.7 V - 2 V), A hollow glass beaker/test tube-housing, A resistor (50 Ω - 100 Ω), Connecting wires-including the long one that will be used as a suspender of the lamp (approximately 5 m), The cork/rubber stopper that fits in the tube, The key/switch, The source/battery (6 V - 12 V), and The battery holder.
First, the two LEDS were connected in series the correct way round that is, anode to cathode connection as shown in Figure 1.
LEDS can be damaged by heat when soldering, but the risk is small unless you are very slow. No special precautions for soldering most LEDS. Second, connect such LEDS in series with a resistor to limit the current to a safe value because if the LEDS are directly connected to a battery or power supply they can be destroyed almost instantly since too much current will pass through and burn them out. Third, Connect the LEDS & resistor to the power supply/battery as shown in Figure 2.
Figure 1. LEDs in series connection.
Figure 2. LEDS and resistor connected to the power supply.
Fourth, Calculating LEDS resistor value, to figure out which resistor to use, the following formula used;
where: = power supply voltage, = sum of LEDS voltage as shown in Figure 3, I = LED current.
Fifth, drill a hole into the middle of the cork/rubber stopper that fits into the beaker/test tube. This hole is used to thread out the wires, for positive and negative terminals of the circuit which will be connected to the switch and battery. Then, place the LEDS into the test tube, and then secure the cork/rubber stopper into the test tube top. Wrap the seam with black tape, and then wrap black tape securely around the wire and stopper to cover up the gaps in this hole. After completing all the steps, thus connect the two wires to their respective terminals-positive and negative of the battery to complete the circuit; the device is ready for use.
3. Results and Discussion
The testing of the LED lamp, it was dipped into the container of water to check the intensity of light produced. This is to check if the intensity of light will attract fish. The LED lamps were left on for 6 hours as we expect that the device will work during the night for those 6 hours. These 6 hours is the corresponding time which the candela lamp consumes one liter of kerosene. The target is to check the rate of energy consumption. Figure 4 shows the lamp before immersed in water while Figure 5 shows the lamp immersed in water.
Figure 3. The complete circuit diagram.
Figure 4. Showing underwater LED lamp before immersed in water.
Figure 5. The LED lamp immersed in water (used in this study).
The following were observed when testing the LED lamp; the minimum voltage at which the LED lamp with two LEDS connected in series will light is from 6 V to 12 V maximum, below 6 V the lamp cannot light. The LED lamp produced a satisfactory amount of light which could reasonably attract fish. The 7 batteries managed to run the LED lamp for three nights consecutively. This shows that the voltage was decreasing very slowly as measured by the voltmeter which indicates that the LED lamp conserve the energy much than the candela lamp. The voltage drop was recorded after every two hours and the results are presented in Tables 1-3 and the graphs of voltage drop are presented in Figures 6-8.
Table 1. Results of voltage drop for day one (used in this project).
Figure 6. The graph of voltage drop for day one (used in this study).
Table 2. Results of voltage drop for day two.
Figure 7. The graph of voltage drop for day two.
Table 3. Results of voltage drop for day three.
Figure 8. The graph of voltage drop for day three.
Table 4. The running cost of LED lamp and candela lamp for three days equivalent to 36 hours.
From Tables 1-3, it was observed that the amount of light decreased as days goes on, for day one it was greater as batteries were new and for the two days the voltage was dropping very slowly but the LED lamp managed to produce the reasonable intensity of light for 36 hours. Thus it is assumed that the device can work properly when used in real context of fishing.
Also from Table 4, the LED lamp showed that it is cost effective as it used only 7 dry cells which cost around 2 US Dollar for 36 hours whereas the candela lamp costs 7 US Dollar to buy 6 liters of kerosene to run it for the same 36 hours.
From Table 4, it was observed that the running cost of the LED lamp is cheaper than that of candela. This is approximately four times the running cost of candela lamp. To determine how much energy is consumed by the candela lamp, the study talked to a fisherman from mtera dam and he gave the following details; the candela lamp consumes one liter of kerosene per 6 hours, that is from 1800 hrs the time when they are entering the fishing field up to 0000 hrs, thus for the whole night of 12 hours the candela lamp consumes two liters of kerosene. The cost can also be reduced more by using rechargeable batteries.
The LED lamp is designed and the device is tested to check if it functions well. The device can be run at lower cost than candela lamp. The device is portable, affordable at half a price of candela lamp and is more efficient. During the construction of the LED lamp device it was very difficult to find the white LEDS in our environment (Iringa municipal), that was why we decided to use the green LEDS which are readily available and are functioning in the same way as the white LEDS. It is advised to design underwater using white LEDS. This is due to the reason that light produced by white LEDS is clearer than that of the colored ones. In this way more fish products will be obtained and the price of fish in the market will be reduced more. Also it is recommended that fishmen in the fishing industry employ the use of underwater LED fishing lamps so as to replace the kerosene based fuel lamps in Tanzania. This cost reveals itself in kerosene price which is increasing daily. The cost of operation can also be reduced by using rechargeable batteries.