LEDs in Parallel: 8 Things You Should Know

Quick answer: Yes, LEDs can be connected in parallel, but equal voltage does not guarantee equal current or brightness. For a resistor-limited circuit, give each LED branch its own resistor to reduce current variation. According to Nichia's application note, separate resistors reduce the variation in forward current.

This guide covers bare LEDs and low-voltage branch calculations. It distinguishes a calculated current from a manufacturer's curve reading and explains why identical resistors do not necessarily produce identical light output. For finished lamps, use the bulb comparison tool to compare lighting choices. Use a qualified electrician for mains-voltage fixture or driver wiring.

Why don't parallel LEDs share current equally?

Forward-voltage variation means that matching part numbers alone does not guarantee matching branch currents. Nichia gives its NSCW215 LED a typical forward voltage of 3.6 V and a maximum of 4.0 V at 20 mA, while describing individual forward voltages ranging from 2.8 to 4.0 V. These are that model's figures, not universal LED specifications. Nichia application note

Nichia also explains that parallel GaN LEDs of the same product can carry different currents at the same applied voltage, producing different luminous intensity and colour. Equal supply voltage therefore does not establish equal output. Nichia application note

The practical distinction is between matching the voltage supplied to the branches and controlling the current in each branch. Wikipedia's LED circuit article likewise says closely matched forward voltages are needed for similar parallel branch currents and light output. Wikipedia: LED circuit

How do series and parallel resistor calculations differ?

For the site's resistor calculation, series mode adds the LED voltage drops; parallel mode uses the forward voltage of one LED for each separate branch. The LED resistor calculator implements these relationships:

The shared-resistor limitation follows from the unequal branch currents shown in Nichia's shared-resistor example (see the application note cited below). Do not divide a total current by the number of LEDs and treat the result as a measured current for every device.

Can you use one resistor for several parallel LEDs?

A shared resistor does not correct differences between the individual LEDs. Closely matched forward voltages are needed for similar branch currents, according to Wikipedia's LED circuit article.

According to Nichia, its shared-resistor example (one resistor in the common leg) uses LEDs described as 3.2 V and 3.8 V at 20 mA and produces roughly a 10:1 current split: about 20 mA versus 2 mA. That ratio is 20 ÷ 2 = 10, not an equal division. The note also warns that forcing both to 3.8 V may exceed the absolute maximum current. Nichia application note

That is a specific example, not a prediction that every shared-resistor circuit has the same ratio. It demonstrates why a shared current limit cannot substitute for evaluating each branch.

How do you calculate each branch resistor?

Use R = (supply voltage − LED forward voltage) ÷ target current, with current in amperes. This is Ohm's law applied to the voltage remaining across the resistor; the same method appears in Wikipedia's LED circuit article.

Worked example with assumed inputs

Assume a 5 V supply, an LED forward voltage of 3.2 V at the intended operating point, and a target branch current of 20 mA. Treat forward voltage as fixed for this calculation. These assumed inputs also match the supposition in Example 1 of Nichia's application note.

1. Convert current: I = 20 ÷ 1,000 = 0.020 A.
2. Find resistor voltage: V_R = 5 − 3.2 = 1.8 V.
3. Calculate resistance: R = 1.8 ÷ 0.020 = 90 Ω.
4. Apply the calculator's nearest-value selection: its E24 table selects 91 Ω, since 91 − 90 = 1 Ω.
5. Recalculate current: I = 1.8 ÷ 91 = 0.0197802 A; 0.0197802 × 1,000 ≈ 19.78 mA.
6. Calculate resistor dissipation using the unrounded current: P = I²R = (1.8 ÷ 91)² × 91 = 3.24 ÷ 91 ≈ 0.035604 W.
7. Apply the calculator's planning figure of a 2× power margin: 0.035604 × 2 ≈ 0.071209 W. Its first listed rating above that is 0.125 W = 125 mW = 1/8 W.

Those current and power results apply to the individual branch resistor. They are calculated estimates under the assumed voltage, not measurements of an assembled circuit. The power margin is the calculator's selection rule, not a cited installation standard.

Why does Nichia report a different current for the other LED?

A fixed-forward-voltage calculation and a current read from an LED curve use different assumptions. According to Nichia, its 5 V example with separate 90 Ω resistors gives LED A, specified at 3.2 V at 20 mA, a current of 20 mA; LED B, specified at 3.8 V at 20 mA, runs at 15 mA. Nichia application note

For a separate worked estimate, assume 5 V supply, a fixed 3.8 V LED drop and a 90 Ω resistor:

• Resistor voltage = 5 − 3.8 = 1.2 V.
• Current = 1.2 ÷ 90 = 0.013333… A.
• Convert to milliamps: 0.013333… × 1,000 ≈ 13.33 mA.

Do not present that arithmetic as the derivation of Nichia's 15 mA result. According to the note, its curve gives 3.06 V at 10 mA and 3.14 V at 15 mA: a voltage difference of 3.14 − 3.06 = 0.08 V accompanies a current difference of 15 − 10 = 5 mA. Forward voltage is not fixed across those operating points. Nichia application note

Will separate resistors guarantee equal brightness?

Separate equal-value resistors reduce variation but do not guarantee equal brightness. According to Nichia, adjusting separate resistors to each LED's forward voltage can produce the same luminous intensity; its equal-resistor example still has unequal currents. Nichia application note

Selecting LEDs from a narrow forward-voltage range is another approach, but Nichia says very narrow binning becomes impractical as available shipments fall and cost rises sharply. That is Nichia's assessment in this note, not a current price comparison. Nichia application note

What should you check before choosing the circuit?

Evaluate the branch current, rather than relying only on a total driver-current figure. The unequal-current comparison above is why each branch needs its own assessment. Wikipedia: LED circuit

• Identify whether the calculation concerns a series string or separate parallel branches.
• Use the intended branch current and the LED forward voltage at that operating point.
• Calculate resistance from the voltage left across the resistor.
• Recalculate current and power after selecting a resistor value.
• Compare branch currents when equal light output matters; identical part numbers do not establish equal current. Nichia application note

FAQ

Are parallel LEDs automatically brighter than series LEDs?

No. Connection type alone does not establish brightness: Nichia shows that current differences change luminous intensity even among parallel LEDs of the same product. Nichia application note

Does every parallel LED need its own resistor?

For the resistor-limited branches discussed here, use a separate resistor in each branch. According to Nichia, this reduces forward-current variation, though equal resistor values do not guarantee identical results. Nichia application note

Can I assume identical LEDs share current equally?

No. LEDs of the same product can draw different currents at the same applied voltage, as explained in Nichia's application note.

Can raising the voltage damage a parallel LED?

Yes. According to Nichia, raising the common voltage in its unequal-forward-voltage example may push an LED beyond its absolute maximum current. Nichia application note

Is the calculated resistor power the power of the whole circuit?

No. In the branch calculation, P = I²R is the power dissipated by that resistor. Total supply power uses P = supply voltage × total supply current.