*Question G6B08:
How is an LED biased when emitting light?*  

*Correct Answer is  D: Forward biased*  

### AI Response: (may contain errors)  

To understand how an LED (Light Emitting Diode) emits light, we need to look at how it is biased:

1. **Correct Answer: Forward biased**
   - An LED emits light when it is forward biased. This means that the positive side (anode) of the LED is connected to a higher voltage than the negative side (cathode). When forward biased, electrons from the n-type material recombine with holes in the p-type material, releasing energy in the form of light. 

2. **Why the other choices are incorrect:**
   - **A: In the tunnel-effect region**  
     - The tunnel-effect region refers to a specific behavior in certain diodes (like tunnel diodes) where quantum tunneling occurs. This is not applicable to LEDs, which operate on recombination of charge carriers.
   - **B: At the Zener voltage**  
     - Zener voltage is associated with Zener diodes, which are designed to operate in reverse bias to maintain a constant voltage. LEDs do not emit light in this condition.
   - **C: Reverse biased**  
     - When an LED is reverse biased, it does not conduct current and therefore does not emit light. In fact, excessive reverse bias can damage the LED.

3. **Useful rules of thumb:**
   - LEDs typically require a forward voltage of about 1.8V to 3.3V, depending on the color and type of LED.
   - Always check the datasheet for the specific LED to determine the correct forward voltage and current ratings to avoid damage.

In summary, for an LED to emit light, it must be forward biased, allowing current to flow and enabling the recombination of electrons and holes, which produces light.