A 5mm Red LED is one of the most common and widely used light-emitting diodes in electronics. Here’s a complete overview: 🔹 Basic Details: Type: Through-hole LED (5mm diameter package) Color: Red (wavelength ~620–630 nm) Forward Voltage (Vf): ~1.8V – 2.2V (typical) Forward Current (If): ~20mA (recommended operating current) Viewing Angle: ~20°–60° (varies by manufacturer) Polarity: Anode (+): Longer lead Cathode (–): Shorter lead, flat edge on casing 🔹 Working Principle: When a suitable forward voltage is applied across the LED, electrons recombine with holes in the semiconductor material, releasing energy as visible red light. Must always use a current-limiting resistor in series to avoid burning out the LED. 🔹 Typical Resistor Calculation: To connect a 5mm Red LED to a 5V supply: 𝑅 = 𝑉 𝑠 𝑢 𝑝 𝑝 𝑙 𝑦 − 𝑉 𝑓 𝑜 𝑟 𝑤 𝑎 𝑟 𝑑 𝐼 R= I V supply ​ −V forward ​ ​ 𝑅 = 5 𝑉 − 2 𝑉 0.02 𝐴 = 150   Ω R= 0.02A 5V−2V ​ =150 Ω So, use a 150Ω resistor (or nearest standard value like 180Ω). 🔹 Applications: Power indicators on circuits and devices DIY electronics and Arduino projects Status indicators in instruments and control panels Decorative lighting, toys, and displays Low-cost optical signaling