If a light emitting diode is illuminated, the diode must be

If a light emitting diode is illuminated, the diode must be

• A. Reverse biased.
• B. Forward biased.
• C. Unbiased.
• D. In conduction with reverse direction.

Answer: (B)

Light from an LED comes from the forward-biased injection of carriers into its active region. When the anode is more positive than the cathode, the p-n junction allows electrons and holes to recombine there, and that recombination releases photons, producing light. This forward biasing is what makes the LED emit. If the diode is reverse biased, the current is minimal and there isn’t enough carrier injection in the active region to produce light, so no illumination occurs. An unbiased device has no driving current, so it won’t emit light either. Describing operation as “in conduction with reverse direction” isn’t how LEDs are used to emit light, and reverse current is not the normal method for producing illumination. So forward bias is required for light emission.

Light from an LED comes from the forward-biased injection of carriers into its active region. When the anode is more positive than the cathode, the p-n junction allows electrons and holes to recombine there, and that recombination releases photons, producing light. This forward biasing is what makes the LED emit.

If the diode is reverse biased, the current is minimal and there isn’t enough carrier injection in the active region to produce light, so no illumination occurs. An unbiased device has no driving current, so it won’t emit light either. Describing operation as “in conduction with reverse direction” isn’t how LEDs are used to emit light, and reverse current is not the normal method for producing illumination.

So forward bias is required for light emission.