LED Resistor Table - IF/VF by Color

Clickable table with typical VF (forward voltage) and recommended currents. Expand a row for ready-reckoner resistor values and notes. Includes a live calculator.

IF / VF by LED Color (click a row for details)

Values are representative of common 3-5 mm indicator LEDs at ≈20 mA (unless noted). Actual datasheets vary by die/chemistry.

Color Wavelength (nm) Typical VF @ 20 mA VF Range Common IF (mA) Notes
IR (940 nm) 850-9501.2 V1.1-1.4 V5 / 10 / 20 Photodiodes/cameras; invisible to eye.
Red 620-6352.0 V1.8-2.2 V2 / 10 / 20 Very efficient at low currents for indicators.
Orange 600-6102.0 V1.9-2.2 V2 / 10 / 20 Similar to red/yellow Vf.
Amber 585-5952.05 V1.9-2.2 V2 / 10 / 20 Traffic indicator color family.
Yellow 585-5952.1 V2.0-2.3 V2 / 10 / 20 Good visibility at modest currents.
Green (AlInGaP) 565-5752.1 V1.9-2.3 V2 / 10 / 20 "Old-school" green; lower Vf than InGaN green.
Green (InGaN) 520-5353.2 V2.8-3.4 V2 / 10 / 20 Newer chemistry; higher brightness, higher Vf.
Blue 460-4803.2 V2.8-3.4 V2 / 10 / 20 Often bright even at 2-5 mA.
Royal Blue 440-4553.3 V3.0-3.6 V5 / 10 / 20 Peak near 450 nm; aquarium/UV-adjacent uses.
White Broad (phosphor)3.2 V2.8-3.4 V2 / 10 / 20 Blue die + phosphor; Vf similar to blue.
UV 365-4053.5 V3.2-3.8 V5 / 10 / 20 Handle safely; avoid eye/skin exposure.

Click a row to reveal a ready-reckoner (3.3 V, 5 V, 9 V, 12 V) for 5 mA / 10 mA / 20 mA and notes on power rating.

R Calculator (single or series LEDs)

Enter values and press Calculate.

Worked Examples

  1. 1x Red LED (VS=5 V, VF=2.0 V, I=10 mA)
    R = (5 - 2.0)/0.010 = 300 Ω
    PR = I²R = 0.01²x300 = 0.03 W → ¼ W (0.25 W) resistor is ample.
  2. 2x Blue in series (VS=12 V, VF=3.2 V each, I=15 mA)
    Total drop = 2x3.2 = 6.4 V
    R = (12 - 6.4)/0.015 ≈ 373 Ω → choose nearest E-series: 390 Ω.
    PR = 0.015²x390 ≈ 0.088 W → ¼ W OK; ½ W for margin in warm enclosures.
  3. White LED from 3.3 V rail (VF=3.2 V, I=5 mA)
    R = (3.3 - 3.2)/0.005 = 20 Ω (very small headroom).
    If LED dims or rail sags, increase R or use a higher rail / lower current.

Cheat Sheet

NeedFormulaTip
Resistor for n series LEDs R = (VS - n·VF)/I V in volts, I in amps. If result ≤ 0, rail too low.
Resistor power PR = I²·R = (VR·I) Choose next standard wattage above PR, add margin.
Safe headroom VR = VS - n·VF ≥ 0.5 V Aim ≥0.5-1 V across R to reduce sensitivity to sag.
Current units I(A) = I(mA) / 1000 Convert before calculating.
E-series pick Pick nearest ≥R E12: 10% steps; E24: 5% steps; adjust current expectation.

Pro tip For constant brightness across battery sag, consider a small constant-current driver instead of a simple resistor.

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