LED Forward Voltage Chart by Color — from infrared and red to blue, white and UV
Forward voltage (Vf) is the voltage an LED drops across itself when it is lit. You need it for one practical reason: to size the
current-limiting resistor from R=(Vs−Vf)/I. This page consolidates typical Vf by color at the standard 20 mA test point into a single chart,
explains why the number drifts with current and temperature, and links straight to the
LED Resistor Calculator so you can turn a Vf into a resistor in one click.
Forward voltage chart by color
The table below lists the typical forward voltage at 20 mA — the most common datasheet test current — as a range for each color. Vf is set mainly by the LED's semiconductor material, which broadly tracks color: low-energy red and infrared sit near 2 V, while higher-energy blue, white and UV sit near 3 V and above. Treat every figure as a reference range: the same color from different manufacturers can differ by several tenths of a volt.
| Color / type | Typical Vf @ 20 mA | Notes |
|---|---|---|
| Infrared (IR) | 1.2 – 1.6 V | GaAs; below visible |
| Red | 1.8 – 2.2 V | AlGaAs / GaAsP |
| Orange | 2.0 – 2.1 V | GaAsP / GaP |
| Amber / Yellow | 2.0 – 2.2 V | GaAsP / GaP |
| Yellow-green | 2.0 – 2.4 V | GaP |
| Pure green (InGaN) | 2.8 – 3.5 V | true green is high-Vf |
| Blue | 3.0 – 3.6 V | InGaN |
| White (phosphor) | 2.8 – 3.6 V | commonly ≈3.0 – 3.4 V; blue die + phosphor |
| Violet / UV | 3.0 – 4.4 V | shorter wavelength → higher Vf |
A single RGB LED is really three dies in one package, so each channel has its own forward voltage — the red channel behaves like a red LED, while the green and blue channels behave like green/blue LEDs:
| RGB LED channel | Typical Vf @ 20 mA |
|---|---|
| Red channel | ≈ 2.0 V |
| Green channel | ≈ 3.2 V |
| Blue channel | ≈ 3.2 V |
⚠️ These are typical ranges, not exact specs. Vf depends on the specific part number, the current you actually run, and temperature. For real design, read Vf from that LED's datasheet at your operating current, or measure it (see below).
Why Vf varies — current and temperature
An LED is not a fixed voltage drop. Two physical effects move Vf around, which is why the chart gives ranges instead of single numbers:
- Forward current: Vf rises as current increases, following the diode's exponential I–V curve. The chart values are quoted at 20 mA; the same LED at 5 mA drops a little less, and at 50 mA noticeably more. Datasheets plot this as the Vf-vs-If curve.
- Temperature: Vf drops slightly as temperature rises (a negative temperature coefficient, very roughly a couple of millivolts per °C per junction). A warm LED therefore drops a touch less voltage and draws a little more current — a feedback effect worth keeping in mind for high-power parts.
Because Vf is largest for blue, white and UV LEDs, those leave the smallest voltage headroom across the resistor at a given supply, so supply ripple and temperature drift affect their current the most. When in doubt, size conservatively or use a constant-current driver.
Using Vf to size a resistor
The whole point of knowing Vf is to put a resistor in series with the LED. The supply voltage Vs splits into Vf across the LED and (Vs−Vf) across the resistor, so applying Ohm's law to the resistor gives:
R = (Vs − Vf) / I
Worked example. A USB 5 V supply, a red LED (Vf = 2.0 V from the chart), targeting 20 mA:
R = (5 − 2.0) / 0.02 = 150 Ω
So you would fit a 150 Ω resistor — which happens to be a standard E24 value. Swap in a blue LED (Vf ≈ 3.2 V) and the same maths gives
R = (5 − 3.2) / 0.02 = 90 Ω, rounded up to the nearest standard 91 Ω. That is exactly the calculation the
LED Resistor Calculator runs: enter Vs, the Vf from this chart, and your target current, and it returns the nearest standard resistor and a suggested power rating.
To decode an existing resistor's bands instead, use the Resistor Color Code Decoder.
How to measure Vf yourself
If you do not have the datasheet, a multimeter gives you the real number in seconds:
- Set the multimeter to diode mode (the ▶︎| symbol).
- Touch the red (+) probe to the anode (the longer leg) and the black (−) probe to the cathode (the flat side / shorter leg).
- The LED should glow faintly and the display reads the forward voltage in volts — this is Vf at the meter's small test current (usually well under 1 mA), so the real Vf at 20 mA will be a little higher.
- If the display reads
OL/ open, swap the probes — you had it reverse-biased.
Diode mode tests at a tiny current, so the reading is on the low side of the chart. For the operating Vf at 20 mA, add a small margin or read the datasheet curve.
FAQ
- Does an LED forward voltage depend on the current?
- Yes. Forward voltage (Vf) rises with forward current because the LED follows an exponential I–V curve. The values in this chart are quoted at the common 20 mA test point. Run the same LED at 5 mA and Vf is a little lower; push it to 50 mA and Vf climbs. For accurate work, read Vf at your actual operating current from the datasheet curve rather than assuming a single number.
- What forward voltage should I use for a white LED?
- A standard phosphor-converted white LED drops roughly 2.8–3.6 V at 20 mA, most commonly around 3.0–3.4 V, because the underlying chip is a blue InGaN die. If you are sizing a resistor and only have one number to use, take the upper end (≈3.2–3.4 V) to stay conservative, then confirm against the specific LED datasheet.
- Can I just use 2 V for any LED?
- No. 2 V is only a reasonable estimate for red, orange and yellow LEDs. Green, blue, white and UV LEDs drop roughly 3.0–3.6 V (UV can reach 4.4 V), so assuming 2 V for them makes your resistor too small and pushes the current over target. Pick the Vf that matches the LED color, or measure it.
- Does the color always predict the forward voltage?
- Mostly, but not exactly. Vf is set by the semiconductor material and chemistry, which broadly tracks color, so the color gives a good range. However, two LEDs of the same color from different manufacturers can differ by several tenths of a volt, and Vf also shifts with current and temperature. Treat color as a quick estimate and defer to the datasheet for the real value.