What Is an LED (Light Emitting Diode)?
An LED (Light Emitting Diode) is a diode that emits light when current flows through it in the forward direction. With low power consumption and long life, it's the foundation of lighting and indicator work.
How Does It Work?
Under forward bias, electrons change energy level and the released energy is emitted as photons (light). The semiconductor material determines the color of the light.
Color and Forward Voltage
| Color | Typical Vf |
|---|---|
| Red | ~1.8–2.0 V |
| Green | ~2.0–2.2 V |
| Blue / White | ~3.0–3.4 V |
Current-Limiting Resistor (a Must!)
An LED is never connected directly to a source; a series resistor is essential. For a 5 V source, a 2 V red LED and 10 mA: R = (5 − 2) / 0.01 = 300 Ω (Ohm's law).
Polarity
An LED is polarized: the long leg is the anode (+) and the short leg is the cathode (−). Installed backwards, it won't light.
Where Is It Used?
Indicator lights, lighting, display backlights, infrared remote controls and optical communication.
Special LED Types
Standout special types include the RGB LED that gives three colors in one package, the high-power LED for lighting, the infrared (IR) LED used in remote controls, and the laser diode that produces a coherent beam.
Common Mistakes
- No resistor: the LED instantly burns out from over-current.
- Installing it backwards: with wrong polarity it gives no light.
- Assuming a blue/white LED is 2 V: their forward voltage is high; size the resistor accordingly.
Frequently Asked Questions
Can I connect an LED directly to a battery?+
Which leg is positive?+
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