LED Colors & Forward Voltage

Vf ranges, wavelengths, semiconductor materials, and current ratings for all common LED types

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LED Forward Voltage Reference

πŸ”
Color & Notes ↕ Ξ» (nm) ↕ Vf @ 20 mA ↕ Semiconductor If max ↕

Key Facts

Forward voltage basics

LEDs require a minimum forward voltage (Vf) to conduct and emit light. Unlike resistors, they do not self-limit current β€” always use a series resistor or constant-current driver. Vf varies with color (semiconductor material) and increases slightly at lower temperatures.

Standard vs. high-brightness

Standard LEDs (5 mm, ~20 mA) have Vf values listed here. High-power LEDs (1 W, 3 W, 5 W) typically have similar Vf but run at 350 mA–1 A β€” use a constant-current driver. SMD LEDs (0402–5050) have similar Vf, check the datasheet for If_max.

Resistor formula

R = (Vcc βˆ’ Vf) / If

Example: Vcc = 5 V, red LED Vf = 2.0 V, If = 20 mA:
R = (5 βˆ’ 2.0) / 0.020 = 150 Ξ© β†’ use 150 Ξ© (E24)

White LED note

White LEDs use a blue or UV GaN die with a phosphor coating. Their Vf is therefore similar to blue LEDs (~2.9–3.5 V), not 2 V. Using a 2 V resistor calculation for white LEDs will over-drive them.

RGB LED β€” wiring and Vf per channel

Common cathode vs. common anode

  • Common cathode: all cathodes share GND; each anode gets its own resistor to Vcc β€” easier with GPIO HIGH = ON
  • Common anode: all anodes share Vcc; each cathode gets its own resistor to GND β€” GPIO LOW = ON (inverted logic)
  • 5 mm RGB through-hole: 4 pins (R, G, B, common)

Calculate resistors per channel

  • Red: Vf β‰ˆ 2.0 V β†’ R = (5βˆ’2.0)/0.020 = 150 Ξ©
  • Green: Vf β‰ˆ 3.2 V β†’ R = (5βˆ’3.2)/0.020 = 91 Ξ©
  • Blue: Vf β‰ˆ 3.2 V β†’ R = (5βˆ’3.2)/0.020 = 91 Ξ©
  • Each channel needs its own resistor β€” never share one
IR & UV LEDs β€” safety and usage

Infrared LEDs

  • 850 nm / 940 nm most common (remote controls, sensors)
  • Invisible to naked eye β€” use a camera/phone to verify emission
  • Vf lower than visible LEDs (~1.2–1.5 V); calculate resistor carefully
  • Often pulsed at high currents (up to 1 A peak) in burst mode

UV LEDs

  • 365–405 nm: resin curing, banknote verification, fluorescence
  • Do not look directly into UV LED β€” eye damage risk
  • High Vf (3.0–4.5 V) β€” similar to blue/violet GaN
  • 395–405 nm "near UV" is safer for general use than 365 nm