Working Principle of an LED:
Step 1 (Governing Principle): [1 Mark]
An LED (Light Emitting Diode) is a heavily doped $p-n$ junction diode which emits spontaneous radiation when forward biased. The working principle is based on Electroluminescence. When the diode is forward biased, electrons from the $n$-region and holes from the $p$-region are injected into the junction region. These charge carriers recombine, and the energy released during recombination is emitted in the form of photons. If the semiconductor material has a band gap $E_g$, the energy of the emitted photon is approximately:
$$h\nu \approx E_g$$where $h$ is Planck's constant and $\nu$ is the frequency of the emitted light.
Step 2 (Advantages): [1 Mark]
- Low operational voltage and less power consumption: LEDs operate at very low voltages compared to conventional incandescent bulbs.
- Fast action and long life: They have a very fast switching time (no warm-up time required) and possess high durability/longevity.
Step 3 (Disadvantages): [1 Mark]
- Temperature sensitivity: The performance and light output of an LED are highly dependent on the ambient temperature.
- High initial cost: The manufacturing process of high-quality semiconductor materials makes them more expensive than traditional lighting sources.
💡 EL10 Concept Insight:
Think of an LED like a tiny energy-swapping machine: when electricity pushes electrons and holes together, they "fall" into each other and release their extra energy as a flash of light instead of just wasting it as heat.