3Mechanical - Experiment Light emitting diode - Practical PDF

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Experiment No. 3 Optoelectronic Device: Light Emitting Diode

Objectives: At the end of this experiment, the students are expected to: 1. be familiar with light emitting diodes, its symbol, characteristics and uses. 2. know the different applications of a light emitting diode. 3. identify the different elements used to produce a variety of colors emitted by the device.

Materials: Qty 1.

VOM

1.

Medium size LED (red)

1.

Analog Trainer

2.

Resistor ( 470 Ω )

1.

Resistor ( 1 kΩ )

1.

Resistor ( 1.5 kΩ )

1.

Resistor ( 2.2 k Ω ) Connecting Wires

Theories/Principles: Electrons flowing through a PN junction experience similar transition in energy level, and emit radiant energy as they do so. The frequency of this radiant energy is determined by the crystal structure of the semiconductor material, and the elements comprising it. Some semiconductor junctions, composed of special chemical combinations, emit radiant energy within the spectrum of visible light as the electrons transition energy levels. Simply put, these junctions glow when forward biased. A diode intentionally designed to glow like a lamp is called a light-emitting diode, or LED. Diodes made from a combination of the elements gallium, arsenic, and phosphorus (called gallium arsenide-phosphide) glow bright red, and are some of the most common LEDs manufactured. By altering the chemical constituency of the PN junction, different colors may be obtained. Some of the currently available colors other than red are green, blur, and infra-red (invisible light at a frequency lower than red). Other colors may be obtained by combining two or more primary-color (red, green, and blue)

LEDs together in the same package, sharing the same optical lens. For instance, merging a red LED with a green LED will produce a yellow LED. Light Emitting Diodes are used primarily as indicator devices. So an operator can tell whether or not a specific voltage is present in a circuit. Like any other diode, it will pass current in only one direction. It will only glow when forward biased. When reverse biased, the LED will remain off. To limit a current in the forward bias condition flowing to an LED, a series resistor should be connected to the circuit. LEDs can be used to display any numerical digit by arranging seven bars or segments in a square eight shape commonly called the “seven segment display”. Symbol: Light-emitting diode (LED) Anode

Cathode Procedures: 1. Construct the circuit of figure 1 using a series resistor value of 2.2 kΩ. 2. Set the voltage source to an initial value of 3 volts. 3. Measure the current through the circuit, voltages across each component and record them on table1. 4. Increase the voltage source to 5 volts and repeat procedure no. 3. 5. Increase the voltage source to 10 volts and repeat procedure no. 3. 6. With a voltage source of 10 volts, replace the 2.2 kΩ resistor with a 470 Ω resistor. 7. Repeat procedure no. 3 and record them on table 2. 8. Replace the 470 Ω with a 1 kΩ resistor and repeat procedure no. 3. 9. Replace the 1 kΩ with a 1.5 kΩ resistor and repeat procedure no. 3. Wiring Diagram:

Figure 1: Basic LED Circuit

Data and Results: Voltage Source

Is

ILED

VR

VLED

3 Volts

967.26 µA

967.25 µA

2.13V

872.01mV

5 Volts

1.83mA

1.83mA

4.02V

976.37mV

10 Volts

3.99mA

3.99mA

8.78V

1.22V

Table 1

Table 2 Series Resistance

Is

ILED

VR

VLED

470 Ω

16.00mA

16.00mA

7.52V

2.48V

1 kΩ

8.32mA

8.32mA

8.32V

1.68V

1.5 kΩ

5.73mA

5.73mA

8.60V

1.40V

O ore the lower e lower value of current and voltage will be measured in each component including the battery, resistor and LED (Light emitting diode). The values of current are changing from µA to mA and mV to V in voltage by the changes rendering the indicated values of the battery. Otherwise in observing the LED (Light emitting diode), in each particular replaced value of voltage source there is no red light emitting by the LED when the voltage source has ranging in 3-5 voltage but, when it replaced into 10 volts the red light was already shown. Then, for the table 2 the voltage source has a constant value which is 10 volts and the resistor’s value has been replaced into 470 Ω, 1k Ω and 1.5 k Ω. When the resistor’s value is lower or in ohms the current and voltage involves or measured in each component has gained a higher value. On the other hand, as the resistor’s value is become higher the lower value of current and voltage will be measured. Despite, of these changes the LED (Light emitting diode) is also constantly showed a red light.

Analysis of results and conclusion: As an analysis, based on the table 1 inputted values the lower value of voltage accompanied by the battery (voltage source), the lower value of current (from µA to mA) and voltage (from mV to V) will flow in a closed circuit. Therefore, we can conclude that as the lower values given by the voltage source, the lower values of current and voltage will be measured in each component inside the closed circuit and vice versa. Also, when the voltage value from the battery is ranging from 3-5 volts there will be no red light appears in the LED itself. But when the voltage source has 10 volts the red light is showed in LED component. In which, it indicates that the red light is appearing by having a higher value of voltage from the battery (voltage source) that is probably sustained the needed number of volts to light up a certain bulb or the LED component. For the table 2, as the resistor’s values are lowered the higher amount of current and voltage will be measured in the circuit. When the resistor’s value is in ohms (lowest value of resistor), therefore the current and voltage flows in a closed circuit will became higher. Because, of the resistor was only the divider of the current and the voltage and it is the reason why the changes of values in each component were opposite to the inputted value of the resistor itself. And, as the voltage source has a higher value or in 10 volts, there will be a constant red light appearing in the LED (light emitting diode) as it was already sustained for the value needed to light an LED was enough.

Question: 1. What are other color varieties of an LED and enumerate the different elements used.

LEDs produce different colors by using various materials which produce photons at different wavelengths. Those individual wavelengths appear as light of different colors. LEDs use materials that can handle the necessary levels of electricity, heat, and humidity. High-brightness red and amber LEDs use the aluminum indium gallium phosphide (AlInGaP) material system. Blue, green and cyan LEDs use the indium gallium nitride (InGaN) system. Together, AlInGaP and InGaN cover almost the entire light spectrum, with a gap at green-yellow and yellow. One method of achieving a larger spectrum of colors is to mix different colors of LEDs in the same device. Combining red, green, and blue LEDs in a single LED device, such as a lighting fixture or multi-chip LED, and controlling their relative intensities can produce millions of colors. Additionally, combining red, green, and blue in equal amounts produces white light....