Introduction

Holiday lights offer a fun and familiar way to explore how electrical circuits work. Modern LED holiday lights are wired in parallel, so one bulb burning out doesn’t turn off the rest. Many older incandescent holiday lights were wired in series, meaning if one bulb failed, the entire string went dark. 

In this activity, students recreate both types of holiday lights using Play-Doh, colorful LED diodes, and a 9-volt battery. They will investigate LED polarity, build simple circuits, and compare how electricity flows differently in series and parallel arrangements. 

This Holiday Lights Play-Doh Circuits activity is a spin-off of our Play-Doh Circuits Hands-On, which includes extensions on insulators and conductors, Ohm’s Law math problems, and circuit diagrams.

Student Objectives

Students will be able to

• Identify the positive (anode) and negative (cathode) leads of an LED diode.
• Build and test a parallel circuit. 
• Build and test and series circuit. 
• Explain why a missing LED diode affects parallel and series circuits differently.
• Connect their observations to the behavior of real strings of holiday lights. 
• Describe how the number of LEDs in a circuit affects brightness due to changes in voltage distribution (series) or current distribution (parallel).

Materials (per group)

• Student Handout
• 5mm LED diodes (4-6)
• 9-volt battery
• 2 alligator clips
• 3-4 small balls of Play-Doh, less than ½ an inch in diameter

Optional Extension: Strand of holiday lights

Procedure

1. Divide students into groups of 2 or 3, and provide them with the Student Handout. 
2. Students will follow the instructions on the Student Handout to set up their circuits. 
3. In Part 1, students explore LED polarity, identifying the positive and negative leads of their LED diodes.
   Teacher Tip: To remember which end is positive, tell students you’ll always get farther by being positive (the anode – the longer lead – is positive). 
4. In Part 2, students build a simple series circuit and observe the effect of a missing LED diode.
5. In Part 3, students build a simple parallel circuit and observe the effect of a missing LED diode.
6. In Part 4, students discuss the differences in current and voltage distribution in series and parallel circuits, and how they affect brightness. 
7. In Part 5, compare the brightness and reliability of lights in series and parallel circuits, and connect their learning to the workings of real holiday lights, past and present. 
8. Optional Extension: If you want to extend the learning with a hands-on, real-world example, bring in an actual strand of holiday lights from home. Let students test what happens when a bulb is removed—does the entire strand go dark (series), or do the remaining lights stay on (parallel)? This gives students the opportunity to directly connect their Play-Doh circuits to the behavior of real holiday lights.
9. Optional Challenge: Create a pre-built model of a series or parallel circuit, where something is wired incorrectly. For example, conductive pieces are touching, an LED diode is placed backwards, an alligator clip is not attached correctly, etc. Challenge students to analyze the model visually and diagnose why the LED diode won’t turn on.