What do I need to build a simple LED circuit?

You need three things: a power source (like a 9V battery or two AA batteries), an LED, and a resistor. The resistor limits the current so the LED doesn't burn out. You'll also need a breadboard and jumper wires, or you can twist the component leads together for a quick test.

Why do I need a resistor with an LED?

An LED has very low forward resistance. Without a resistor, too much current flows through the LED, overheating and destroying it — often within seconds. The resistor limits the current to the LED's safe operating range, typically 10–20 mA for standard LEDs.

What resistor value do I need for an LED?

Use the formula R = (V_supply - V_LED) / I_LED. For a 9V battery with a red LED (2V forward voltage, 20 mA): R = (9 - 2) / 0.02 = 350Ω. Use the nearest standard value, 330Ω or 470Ω. A higher value is always safe — it just makes the LED slightly dimmer.

How do I know which LED leg is positive?

The longer leg (lead) is the anode (positive). The shorter leg is the cathode (negative). If the legs have been trimmed, look at the flat edge on the LED's plastic body — the flat side marks the cathode (negative). Current flows from anode to cathode.

Why is my LED not lighting up?

The most common causes are: the LED is backwards (swap the legs), the resistor value is too high (try a lower value), the battery is dead, or there's a loose connection. Try reversing the LED first — this fixes the problem about half the time.

Can I connect an LED directly to a battery without a resistor?

Only with a coin cell (3V CR2032) because its high internal resistance naturally limits current. With any other battery (AA, 9V, etc.), you must use a resistor or the LED will burn out quickly. Always use a resistor for reliable, long-lasting circuits.

Simple LED Circuit

A simple LED circuit is the most basic electronics project: a battery, a resistor, and an LED connected in series. It demonstrates the core principles of voltage, current, and resistance in a hands-on way and takes less than five minutes to build. If you've never built a circuit before, this is where to start.

What you need

Component	Specification	Approximate cost
Battery	9V battery (or 2× AA with holder)	$2–5
LED	Standard 5mm, any color	$0.10
Resistor	330Ω–470Ω, ¼W	$0.05
Breadboard	Any size	$3–5
Jumper wires	22 AWG solid core	$3 (kit)
Battery snap connector	9V snap with leads (if using 9V)	$1

How the circuit works

The battery provides voltage — the electrical pressure that pushes current through the circuit. Current flows from the battery's positive terminal, through the resistor, through the LED (which emits light), and back to the negative terminal.

The resistor limits the current to a safe level. Without it, the LED's low forward resistance would allow too much current to flow, destroying the LED. The resistor and LED are in series, so the same current flows through both.

The voltage splits between the resistor and the LED. The LED drops a fixed voltage (its "forward voltage"), and the resistor drops the remainder. For a 9V battery and a red LED with a 2V forward voltage, the resistor drops 7V.

Calculating the resistor value

The resistor value depends on three things: supply voltage, LED forward voltage, and desired current. The formula is:

R = (V_supply - V_LED) / I_LED

Example: 9V battery, red LED

Parameter	Value
Supply voltage (V_supply)	9V
LED forward voltage (V_LED)	2V (typical red LED)
LED current (I_LED)	20 mA (0.02 A)

R = (9 - 2) / 0.02 = 350Ω

The nearest standard resistor values are 330Ω (slightly brighter, 21 mA) or 470Ω (slightly dimmer, 15 mA). Both are safe. When in doubt, go with the higher value — a dimmer LED is better than a dead one.

Use our LED resistor calculator to find the value instantly for any LED color and supply voltage. Need help reading the color bands on the resistor? We have a guide and calculator for that too.

LED forward voltages by color

LED color	Typical forward voltage
Red	1.8–2.2V
Orange	2.0–2.2V
Yellow	2.0–2.4V
Green	2.0–3.5V
Blue	3.0–3.5V
White	3.0–3.5V

Step-by-step build

Method 1: On a breadboard

Connect the 9V battery snap's red wire to the breadboard's positive power rail.
Connect the battery snap's black wire to the negative (ground) rail.
Place one end of the 330Ω resistor in the positive power rail. Place the other end in any row in the main area (e.g., row 10).
Place the LED's longer leg (anode, positive) in the same row as the resistor's other end (row 10).
Place the LED's shorter leg (cathode, negative) in a different row (e.g., row 12).
Use a jumper wire to connect that row (row 12) to the negative power rail.
Connect the battery. The LED should light up.

Method 2: Direct wiring (no breadboard)

Twist one leg of the resistor around the LED's longer leg (anode).
Connect the other end of the resistor to the battery's positive terminal (red wire).
Connect the LED's shorter leg (cathode) to the battery's negative terminal (black wire).
The LED lights up.

Adding a switch

To control the LED with a push button or toggle switch, place the switch in series with the circuit — anywhere in the loop. The simplest approach:

Disconnect the resistor from the positive rail.
Connect one terminal of the switch to the positive rail.
Connect the other terminal of the switch to the resistor.

When the switch is open, the circuit is broken and no current flows. When closed, current flows through the resistor and LED as before.

Adding more LEDs

LEDs in series

Connect LEDs end-to-end (anode of one to cathode of the next) with a single shared resistor. The supply voltage must be higher than the sum of all LED forward voltages. With a 9V battery and red LEDs (2V each), you can run at most 3 in series (6V total drop, leaving 3V for the resistor).

R = (9 - (2 × 3)) / 0.02 = 150Ω

LEDs in parallel

Each LED needs its own resistor. Do not share a single resistor among parallel LEDs — slight differences in forward voltage cause uneven current distribution, and one LED may take all the current and burn out. See our LED wiring guide for detailed parallel wiring diagrams.

Troubleshooting

Symptom	Likely cause	Fix
LED doesn't light	LED is backwards	Flip the LED (swap legs)
LED doesn't light	Dead battery	Test battery voltage with multimeter
LED doesn't light	Loose breadboard connection	Re-seat components, check row connections
LED is very dim	Resistor value too high	Use a lower value (e.g., 220Ω instead of 1kΩ)
LED burned out	No resistor or value too low	Replace LED, add/increase resistor
Resistor is hot	Resistor value too low, too much current	Use a higher value resistor

What you've learned

By building this simple circuit, you've applied the core concepts of electronics:

Voltage — the battery provides the push (9V)
Current — charge flows through the circuit (~20 mA)
Resistance — the resistor limits current to protect the LED
Ohm's Law — you calculated the resistor using V = I × R
Series circuit — components share the same current path
Polarity — the LED only works in one direction

Next steps

Now that you've built your first circuit, try the Arduino LED blink project to make the LED flash using code, or build a light sensor circuit that turns the LED on automatically in the dark.

Summary

A simple LED circuit uses a battery, resistor, and LED in series. The resistor limits current to protect the LED — calculate it with R = (V_supply − V_LED) / I_LED. Connect the LED's longer leg to positive and shorter leg toward ground. This project teaches voltage, current, resistance, and Ohm's Law in a single hands-on build.

Simple LED Circuit: Your First Electronics Project