Series vs Parallel
Wire two LEDs two different ways and watch the brightness change.
What you’ll learn
- A series circuit splits voltage between parts.
- A parallel circuit gives every part the full voltage.
- Why holiday lights used to all go out when one bulb died.
What you need
| Item✓ | Qty | ~Cost | Where to buy | |
|---|---|---|---|---|
| 9V battery + snap clip | 9V battery + snap clip | 1 | GHS 23.00 | Any supermarket or hardware store. |
| 220 Ω resistor | 220 Ω resistor Look for red-red-brown stripes. | 1 | GHS 0.75 | Electronics shop or online (Amazon, Adafruit). Look for red-red-brown stripes. |
| Red 5 mm LED | Red 5 mm LED Any colour works; red is brightest. | 1 | GHS 1.50 | Electronics shop or online. Any colour works; red is brightest. |
| Half-size breadboard | Half-size breadboard | 1 | GHS 23.00 | Online (Amazon, Adafruit, AliExpress). |
| Jumper wires | Jumper wires | 4 | GHS 30.00 | Online — usually sold in packs of 30. |
| Extra LED (any colour) | Extra LED (any colour) | 1 | GHS 1.50 | Electronics shop or online. |
| Extra 220 Ω resistor | Extra 220 Ω resistor | 1 | GHS 0.75 | Electronics shop or online. |
| TotalTotal | ~GHS 80.50 | |||
Build it step by step
Build the series side first
Resistor at b3-b8. LED 1 at e8-f8. LED 2 at e10-f10. The same current passes through every part in turn.
Wire it
+rail → a3, b8 → e8, f8 → e10, f10 → −rail. Both LEDs light dimly.
Build the parallel side
Two resistor + LED chains side by side, both fed from the + rail and both returning to the − rail. Each chain gets the full battery voltage.
Compare brightness
Look at the two pairs. Parallel pair = bright. Series pair = noticeably dimmer. Same battery, same LEDs.
Pull one LED out of each side
In the series chain, the surviving LED also goes dark. In the parallel chain, the other one keeps going.
How it works
When parts are in series, they share the battery’s voltage between them. Two LEDs in series each get only half the push, so they’re dimmer. In parallel, every branch reaches both ends of the battery, so each LED gets the whole voltage. That’s why modern holiday lights use parallel wiring — pop one bulb and the others stay lit.
If something’s not working
Only one LED of the parallel pair lights
- · The other branch is missing a wire or has the LED backwards.
Series LEDs are super dim or off
- · Resistor is too big. With two LEDs sharing 9 V, a 220 Ω resistor is fine — 1 kΩ might be too much.
Try this next
Add a third LED to the series chain. What happens?
Use two different colours — does one win the brightness contest?