Question

For emission of light, a light emitting diode (LED) is

• A. always used in reverse biased condition
• B. never used in forward or reverse biased condition
• C. used both in forward and reverse biased condition depending upon application
• D. always used in forward biased condition

Hint:

Physics Tip : LED emits light due to electron-hole recombination.

Answer 1

The Correct Option is D

Step 1: What is LED? LED means Light Emitting Diode. It is a p-n junction diode that emits light when current passes through it.

Step 2: Condition for current flow. A diode conducts significant current in forward bias. In reverse bias, only negligible leakage current flows and no useful light is emitted.

Step 3: What happens in forward bias? When forward biased:
• Electrons from n-side move toward junction.
• Holes from p-side move toward junction.
• Recombination occurs near junction.
• Energy is released as photons (light).

Step 4: Why not reverse bias? Reverse bias increases depletion region and prevents recombination current, so LED does not normally emit light.

Step 5: Conclusion. Hence LED is operated for emission in forward bias only. $$ \therefore \text{Correct option is (D).} $$