Green LED

Composition and Wavelength

The color of the emitted light depends on the band gap energy of the semiconductor material. Green LEDs can be manufactured from a few different material systems, resulting in slight variations in color, brightness, and voltage:

• Standard Green (Yellowish-Green): Often uses Gallium Phosphide ($\text{GaP}$) or Aluminum Gallium Phosphide ($\text{AlGaP}$).
  • Wavelength ($\lambda_D$): Typically around $560\text{ nm}$ to $570\text{ nm}$ (nanometers), which is closer to the yellow-green portion of the spectrum.
  • Forward Voltage ($\text{V}_f$): Usually around $2.0\text{V}$ to $2.2\text{V}$.
• High-Brightness/True Green: Modern, highly efficient green LEDs typically use Indium Gallium Nitride ($\text{InGaN}$).
  • Wavelength ($\lambda_D$): Closer to $520\text{ nm}$ to $530\text{ nm}$ (a “truer” green).
  • Forward Voltage ($\text{V}_f$): Can be significantly higher, often ranging from $3.0\text{V}$ to $3.5\text{V}$ (similar to Blue and White LEDs).

Electrical Requirements

Like all LEDs, a Green LED is a polarized component and must be connected with the correct polarity (forward-biased) and a current-limiting resistor to prevent burnout.

• Forward Current ($\text{I}_f$): Standard LEDs are rated for about $10\text{ mA}$ to $20\text{ mA}$.
• Polarity: The Anode (longer lead) connects to the positive voltage, and the Cathode (shorter lead/flat edge on the casing) connects to the negative (Ground).

Resistor Calculation

The value of the series current-limiting resistor ($R$) is found using Ohm’s Law:

Using an average $\text{V}_f$ of $2.2\text{V}$ for a standard green LED and a $5\text{V}$ supply, targeting $20\text{mA}$ ($0.020\text{A}$):

You would typically choose the nearest standard resistor value, such as $150\ \Omega$.

Common Applications

Green LEDs are used in a variety of status and signaling roles:

• Status Indicators: Commonly signify “Power On,” “Active,” “Safe,” or “Ready” status on electronic equipment, control panels, and appliances.
• Traffic Signals: The primary color for “Go” in traffic lights, requiring highly efficient and durable true-green LEDs.
• RGB Displays: The green sub-pixel is often the most critical for overall display brightness, as the human eye is most sensitive to green light. They are a core component in full-color LED screens, video walls, and display backlighting.
• Horticultural Lighting: While red and blue light are primary for photosynthesis, green light is important for canopy penetration and regulating plant growth deep within foliage.