LED Color Mystery

Sponsored Lesson by KEYSIGHT Technologies

This lesson plan explores different types of inputs and output. It introduces students to measuring circuits physically and with simulations. Students explore how different colored LEDs work in a circuit and learn how to use a multimeter and simulations to measure electrical elements. 

  • Different colored LEDs in electrical circuits
  • Ohm’s Law- the connection between Resistance, Voltage and Current
  • How and why to use a multimeter

Age Levels: 10-17

Materials & Preparation

Basic Circuit & Measurement

  • LEDs (10mm is best) Red, Blue, Geen, Yellow, White –  per student (extra if a leg breaks) 
  • Coin Cell Batteries (3V- CR2023 works) – 2-3 per student (second for testing more LEDs)
  • AA Batteries (9 per team)
  • Battery Holder for AA Batteries (4, 6, 9)
  • Multimeter
  • PlayDoh (1-2 can per team)
  • Computers
  • PHet Simulations (Circuit Construction Kit: DC)

Optional Materials- For an optional challenge

  • Copper Tape – 1ft – 2ft per student 
  • Index Card – Up to 3-5 per student (extra are for testing, mistakes)
  • Table of Possibilities (pipe cleaners, googly eyes, colored paper, feathers, binder clips, paper clips, Tape/Glue, Scissors, Markers, etc). Items are for for decorating and attaching name badge (Optional Challenge)

Exploring Creativity with Colored Light

Light plays a fascinating role in art, transcending mere illumination. Imagine synchronized fireworks displays set to music or the way stained glass comes alive when backlit. With technological advancements, various forms of lighting now express celebrations, thoughts, and ideas.

From concerts to theater productions, lighting adds visual layers and drama. Whether it’s enhancing a dinner setting or transforming a wedding venue, lighting designers have an expansive canvas limited only by their imagination and available resources.

Colored lights add a captivating dimension to our surroundings. Whether it’s the vibrant glow of neon signs, the soft hues of LED displays, or the interplay of colored filters in stage lighting, these luminous variations evoke emotions and set the mood.

Consider how colored lights transform spaces:

  • Ambiance: Warm tones create coziness, while cool blues evoke calmness.
  • Artistic Expression: Artists use colored lights to convey themes, emotions, and narratives.
  • Architectural Highlights: Illuminating buildings with colored lights enhances their architectural features.
  • Celebrations: From holiday decorations to festive events, colored lights bring joy and cheer.

Next time you see a rainbow of colors dancing across a cityscape or illuminating a stage, appreciate the artistry behind these radiant displays!

Design Challenge

Color Confusion

The Challenge: You have been given the challenge of designing and creating a circuit with multiple colored LEDs and exploring the use of the multimeter and “data sheets.”
 

Criteria & Constraints

  • Use a simulation tool to measure your circuit
  • Use a voltmeter to measure voltage and amps.
  • Use Red, Green, Blue, Yellow and White LEDs

Phase 1 : Introduction the Challenge – Whole Class Demo, Observations
Phase 2: Voltmeter, Ohm’s Law, Forward Voltage
Phase 3: Design & Construct a circuit with 2-3  different color LEDs. 

Phase 1: Introduce the Challenge- Whole Class Demo, Observations

  • Read the design challenge and constraints.
  • Introduce the problem to the whole class: Hold up a 3V coin cell battery and test multiple colored LED in parallel.  (Red, White and Blue). So….we need to figure out what this may be happening. First let’s see what combinations work or don’t work.
  • Test Color LEDs in Parallel & Observe: In teams of two to four students observe what happened with different colored LEDs.. Using a 3V coin cell battery and the 10mm LEDs in parallel. Long legs on top of the coin cell battery (+ positive) and short legs on bottom (- negative). Fill out the chart.

  • Discuss together: Why do you think this is happening? Do you see any patterns?
  • What can we do next to try to get them all to light up?
  • Discuss:: Ask a team to share their observations and what they think we can try to do to get that color combo to light up. Explain that we need to analyze the circuit to better understand why this is happening. To do this we need to (1) Understand color LEDs: Attributes that can be found on  “data sheets” (2)  measure its elements (the LEDs and battery) using a voltmeter..
  • “Data Sheet” or Data about Circuit Element/Part

Phase 2: Multimeter, Ohm’s Law, Forward Voltage

  • What is a Multimeter (also called voltmeter)? A multimeter is a  tool used to measure electrical values: voltage (volts), current (amps) and resistance (ohms). You will use the multimeter in a bit, but first let’s learn about Ohm’s Law.
  • To understand a multimeter we must understand Ohm’s Law. It is an equation explaining the relationship between Voltage, Current, and Resistance within electrical circuits.  It is defined as: V = I x R
  • V = Voltage (Voltage is measured in volts)
    Voltage is like the push that gets the electric current moving. It is an electric potential difference between two points on a conducting wire. Voltage comes from various sources such as electric outlets and batteries. 
  • I = Current (Current is measured in amps.)
    Current is the flow of electricity, like water flowing through a pipe. It is charged particles which flow from the voltage source through conductive material to a ground.
  • R = Resistance (Resistance is measured in ohms.) Resistance is the opposition that a material body offers to the passage of an electric current. Insulators (like plastic or an eraser) resist electrical current. The higher the resistance the the higher the voltage needed.

If you know the voltage and the current, you can find the resistance by dividing the voltage by the current. It’s like figuring out how much push it takes to get a certain amount of flow through an obstacle. The more resistance, the more push (voltage) you need to get the same flow (current).

In practice, you would connect the multimeter to the two ends of the object you want to measure. The multimeter sends a small known current through the object and measures how much voltage is needed to push that current through and tells you the resistance in ohms. Source: How to Measure Resistance by WikiHow. Remember, the higher the number of ohms, the more the object resists the flow of electricity.

 

Simulations with Phet and Tinkercad: Ohm’s Law and Multimeter/Voltmeter

  • Have teams of two students play with Phet Ohm’s Law simulation to get a better understanding how voltage, current, and resistance are interconnected. See images from PHet (below). Ohm’s law states  that the voltage across a conductor isdirectly proportional to the current flowing through it.
  • Phet Simulation and/or TinkerCad Circuits: Understanding Your Circuit by Measuring
    Test using the simulation’s multimeter (or voltmeter) and seeing the values of each element in the circuits.
  • Tinkercad Circuits (optional): It is nice you can simulate the circuit using the same materials we are using to create our circuits:  LEDs and coin cell batteries. Unfortunately, you can not edit the voltage for the LEDs…so in this simulation it does not accurately represent the unique colors. However, this is a great tool to prototype if you do not have actual materials and you consider the data sheets.
  • PhET Circuit Construction Kit: DC Click the play button on the image and choose Intro. Have fun testing the voltage of the battery and the LEDs too with the “Voltage Meter.” Test a series and parallel circuit.

    For our Circuit in Series, see if you can create an equation:
    V(Battery) 9V = 3V (LED1) + 3V (LED2) + 3V (LED 3). To learn more visit: https://www.electrical4u.com/voltage-in-series/

    • Kirchhoff’s Voltage Law states that the sum of the voltage around any closed circuit must be zero

In Parallel
V (Battery) 6V = V6 (LED1)= 6V (LED2) = 6V (LED3)
To learn more visit: https://www.electrical4u.com/voltage-in-parallel

See a great example of Ohm’s Law from Instructables: Ohm’s Law: 4 Steps

Challenge 3: Play with a Real Multimeter

Battery Test

Watch the video by DigiKey  Basic of a Multmeter. Every multimeter is slightly different (locations) however the symbols remain the same for all.  Use the manual from your multimeter to learn what the symbols mean and how to best use it. Begin by using your multimeter to test a battery. Put the switch to the voltage section 20 spot. Notice the negative sign. This shows you need to flip the polarity of the tested object. Make sure all students get a chance to test. You can also test LEDs to determine if they are working by putting the switch to the LED symbol and the leds will light up.

   

Color LED Mystery: Increase Voltage?
Test if increasing Voltage will light up all colors. What amount of power (battery voltage) is needed to make all the colored LEDs Light up in parallel?

To make testing easier we will mount our LEDs in PlayDoh. PlayDoh conducts electricity but adds a bit of resistance. In electrical circuits, resistance is like a “crowd” that makes it tougher for electric charges (like tiny electrons) to move around. Resistors keep LEDs from getting too much voltage. Insulators have resistance and the more insulating a material, the more resistance it has. Electrical resistance is the difficulty electricity faces when flowing through a circuit, and resistors are the special parts we add to the circuit to control how much electricity gets through. It’s all about finding the right balance to make our electronic devices work just right!

 

Here is a sample with the Red, White and Blue LEDs. At 3V only Red lights up. All LEDs light up with 4.5V and just get brighter the more voltage. If you keep adding voltage, eventually the power will blow out the LEDs. This is dangerous so stop at 9V. Also this can shorten the life of your LED as well. The PlayDoh acts as a bit of a resistor in our test, but if you wanted to have your LEDs last you would want to add a resistor to the circuit.

The Mystery Solved

All LEDs have a forward voltage (Vf), where they begin to conduct. Different LED colors have different Vf forward threshold voltages. The lower Vf LED conducts and the higher Vf LED doesn’t. So with a 3V battery and a red LED (Vf=1.8V) in parallel with a white LED (Vf=3.2V) and a Blue LED (Vf=3.2) you will see the red one light and white and blue one stay dark. Disconnect the red one and the white and blue one lights up.

To learn more check out this video by Q26: All About LEDs Part 2: Mixing Different Color

Here’s a sampling of some LED colors and their forward voltages (Vf). When in doubt, consult the LED datasheet.

  • Red:1.8V
  • Yellow: 2.1V
  • Green 2.2V 
  • Blue: 3.2V
  • White: 3.2V

Application:
Measuring the circuit & Ohm’s Law

  • What do we know:
    – 4.5V Battery
    – 20mA (.02A) LED Current Standard 
  • Let’s see how  things are with our playdough circuit. By measuring  the elements to see what the current is really running through it.
  • Measure each LED (see image): Red LED is 1.73V, Blue LED is 2.4V and White LED is 2.41 (these pretty much the Data Sheet)
  • Let’s see if we have too much current going through the circuit. 
  • Voltage Drop: VBattery – VLED = 4.5V-2.4V = 2.1V
    V=IR, R=2.1V/.02A= 105 Ohms (resistor needed) Our PlayDoh does have some resistance. Is it not enough or too much?
  • Measure the Current through PlayDoh. It is 63mA (LED is made to carry 20mA). So we need more resistance if we want to have our light last as long as possible. The resistance of PlayDoh depends on its shape and length. “The longer and thinner the PlayDoh the greater the resistance” (Lab – The Resistivity of Play-Doh by Manitoba Association of Physics Teachers). Have fun testing this for yourself.


Armed with all of the above understanding, now…

Optional:  Design and construct a paper circuit with multiple colored LEDs. We will need to use more voltage than one coin cell battery so you can use your battery holder as a stand for your artwork or try to stack multiple coin cell batteries. Have fun by turning it into a piece of art.

Share the Tips and Tricks:

  • Both the LED and coin cell battery have a Positive and Negative end. Notice the positive leg of the LED must connect with the positive side of the coin cell battery and same for the negative side.
  • Test your battery and LED to ensure your components work prior to assembly. Put the long leg of the LED to the top (+) side of the coin cell battery and the short leg of the LED to the bottoms (-) side of the coin cell battery. How many LEDs can the coin cell battery power in parallel? (add more LEDs to your test).
  • Shorting a circuit: Be mindful to not have your copper tape overlap where it shouldn’t- resulting in the breaking of the current flow. (i.e. putting copper tape across the circuit, be careful with the coin cell battery as the side of it is also positive.)
  • The copper tape will be your WIRE. It has adhesive on the back; just peel off the paper.
  • To get good connectivity you need pressure…make sure to press down on the LED legs and consider adding cooper tape both below and on top of the legs
  • Your coin cell battery acts like a switch. When you press on it, it closes the circuit.
  • To keep your light on, tape it down.
  • LED legs can break off easily. Be mindful to not bend too sharply.
  • LED colors can be tricky. To keep it simple use only one color for this project. Each color LED requires a different voltage to light up (for example: Red:1.8V, Yellow: 2.1V, Green: 2.2V, Blue: 3.2V and White: 3.2V). So depending on the combination, it may not work for you to use 3 different color LEDs in this project. To learn more check out this video by Q26: All About LEDs Part 2: Mixing Different Colors

Time Modification

The lesson can be done in as little as 1 class period for older students. However, to help students from feeling rushed and to ensure student success (especially for younger students), split the lesson into two periods giving students more time to brainstorm, test ideas and finalize their design. Conduct the testing and debrief in the next class period.

Physics Behind LEDS :Inside LEDs, tiny electrons play an energy game. When they move, they release light of different colors. Manufacturers choose special materials to create red, blue, green, yellow, and white LEDs. So, it’s like a colorful electron dance party!

Light also travels in waves, but we can’t see them because they’re super tiny! The distance between two peaks of these light waves is called the wavelength. Each color has a specific wavelength. The shorter the wavelength, the higher the forward voltage. See how Red light has larger waves (like gentle hills)  and therefore lower voltage. Whereas Blue light has shorter waves (like speedy bumps) and therefore higher voltage. So, when we talk about wavelength, we’re basically measuring how close or far apart those light wave peaks are. 

To learn more about the color spectrum read this article from Ducksters.com : Physics for Kids: The Science of Light Spectrum

Videos

  • Battery: Powers the circuit. When the battery is in a closed circuit it will convert chemical energy to electrical energy (electricity) to power the circuit (i.e make current flow and light the LEDs)
  • Current: Flow of electrical energy (electricity) through a circuit
  • LED: Type of semiconductor called “Light Emitting Diode” (LED). It will light-up when current is flowing through it. Positive (long) leg is the “anode” and the negative (short) leg is the “cathode”
  • Wire: Conducts electricity and is used to connect components in a circuit 
  • AC: An alternating current (AC) is an electrical current that regularly reverses direction and changes its value constantly with time
  • DC: A direct current (DC) is an electric current that flows through in one direction
  • Closed Circuit: When the switch in the circuit is closed and current can flow
  • Open Circuit: When the switch in the circuit is open and current can not flow
  • Switch: A switch in a circuit is used to open or close the circuit. Closing off or opening the flow of current
  • Short Circuit: When wires that are not supposed to come in contact with each other touch (overlap in someway)
  • Condutor: Material that allows electricity to flow through it
  • Insulator: Material that does not allow electricity to flow through it
  • Resistance: In electrical circuits, resistance is like a “crowd” that makes it tougher for electric charges (like tiny electrons) to move around. Insulators have resistance and the more insulating a material, the more resistance it has. Insulation is measured in resistance. The more insulating a material, the more resistance it has. Electrical resistance is the difficulty electricity faces when flowing through a circuit, and resistors are the special parts we add to the circuit to control how much electricity gets through. It’s all about finding the right balance to make our electronic devices work just right! 
  • Resistor: Resistors can be used to control how much electricity is going to a certain part of your electronic device. For example, in a flashlight, a resistor makes sure that the light bulb gets just the right amount of electricity so it can light up without burning out.
    LEDs are resistors. We measure electrical resistance using a unit called an ohm, symbolized by the Greek letter omega (Ω)  
  • Parallel Circuit: Allows multiple paths for electricity (current) to flow through
  • Series Circuit: Allows one path for electricity (current) to flow through 
  • Ohm’s Law: is an equation explaining the relationship between Voltage, Current, and Resistance within electrical circuits. 
  • Kirchhoff’s Voltage Law: states that the sum of the voltage around any circuit must be zero
  • Multimeter (voltmeter): A multimeter is a  tool used to measure electrical values: voltage (volts), current (amps) and resistance (ohms)
  • Forward Voltage: It is the minimum voltage an LED need to light up
  • Voltage Drop: The current running through a circuit will result in a voltage drop across the components. 
  • Data Sheet: It provides detailed information about a product.

Extension Activities

  • Clean Energy: Discuss the use of LEDs in the world.

SDG 7: Affordable and Clean Energy
“About 50% of global residential lighting sales use LED technology. To align with the Net Zero Emissions by 2050 Scenario, progress in this area must be sustained to 2030 to ensure that all countries sell predominantly LED technology and with increasing efficiency.” Source: Lighting IEA

  • Why are LEDs part of the clean energy strategy?
  • Do you use LEDs in your home, your school, etc?
  • Develop a plan to convert to LED light where it is not currently being used.
Alignment to Curriculum Frameworks
The “Notes” column explains how the lesson connects to STEM topics and a “X” indicates at what level (beginner, intermediate, advanced). Please note a large “X” indicates a strong connection and a small “x” indicates a weaker connection or opportunity to make a connection. 
Science Topics Notes Beginner Intermediate Advanced
Materials & Properties Use of unique materials: copper tape for wire and a coin cell battery (these may be new to students). This paper circuit is the same as building a circuit on a breadboard. Creative use of material for how to wear the name badge. x
Energy Could discuss energy conversion within the battery (chemical to electrical) x
Electricity/Magnetism Basic circuits (series and parallel) X
Physics (light, sounds, heat) Gaining understanding of how LEDs work X

 

Technology  Topic Notes Beginner Intermediate Advanced
Systems Open and closed circuit X
Design & Innovation (EDP) Engineering Design Process (EDP) X

Sustainable Development Goals (SDGs) Alignment – Lessons are aligned based on if the lesson could be used to address any of the SDGs (https://sdgs.un.org/goals).

SDG 7: Affordable and Clean Energy
Ensure access to affordable, reliable, sustainable and modern energy for all.
x Discuss use of LEDs around the world.

DESIGN CHALLENGE: Color Confusion

The Challenge: You have been given the challenge of designing and creating a circuit with multiple colored LEDs and exploring the use of the voltmeter and “data sheets.”

Criteria & Constraints

  • Use a simulation tool
  • Use a voltmeter to measure voltage and amps.
  • Use color LEDs (Red, Blue, Green, Yellow, White)

Phase 1: Whole Class Demo, Observations

  • Test Color LEDs in Parallel & Observe: In teams of two to four students observe what happened with different colored LEDs.. Using a 3V coin cell battery and the 10mm LEDs in parallel. Long legs on top of the coin cell battery (+ positive) and short legs on bottom (- negative). Fill out the chart.

  • Discuss together: Why do you think this is happening? Do you see any patterns? 
  • What can we do next to try to get them all to light up? 
  • Look at the LED datasheet and discuss 

Phase 2: Simulations: Ohm’s Law and Multimeter/Voltmeter 

  • Teams of two students play with Phet Ohm’s Law simulation to get a better understanding how voltage, current, and resistance are interconnected and prepare you for playing with a Multimeter.
  • PhET Circuit Construction Kit: DC.  Click the play button on the image and choose Intro. Have fun testing the voltage of the battery and the LEDs too with the “Voltage Meter.” Test a series and parallel circuit.  

Play with a Real Multimeter
Battery Test 

Watch the video by DigiKey  Basic of a Multmeter. Every multimeter is slightly different (locations) however the symbols remain the same for all.  Use the manual from your multimeter to learn what the symbols mean and how to best use it. Begin by using your multimeter to test a battery. Put the switch to the voltage section 20 spot. Notice the negative sign. This shows you need to flip the polarity of the tested object. Make sure all students get a chance to test. You can also test LEDs to determine if they are working by putting the switch to the LED symbol and the leds will light up.

Color LED Mystery: Increase Voltage?
Test if increasing Voltage will light up all colors. What amount of power (battery voltage) is needed to make all the colored LEDs Light up in parallel?

To make testing easier we will mount our LEDs in PlayDoh. PlayDoh conducts electricity but adds a bit of resistance. In electrical circuits, resistance is like a “crowd” that makes it tougher for electric charges (like tiny electrons) to move around. Resistors keep LEDs from getting too much voltage. Insulators have resistance and the more insulating a material, the more resistance it has. Electrical resistance is the difficulty electricity faces when flowing through a circuit, and resistors are the special parts we add to the circuit to control how much electricity gets through. It’s all about finding the right balance to make our electronic devices work just right! 

Use the voltmeter to test one of your circuits (Red, White and Blue). Test the voltage and the current and use what you learned from Ohm’s law.

  • How much current is running though your circuit? Test the LED and the PlayDoh. If it is more than the 20mA allowed on the data sheet it is too much.
  • If too much, what will happen to the LEDS?
  • Using Ohm’s Law, calculate resistance needed for your circuit.
  • What are some options for you to increase resistance with the PlayDoh alone?
  • If time, try to increase the resistance in your circuit by iterating on the shape of the playdoh “wires.”
  • Discuss “Electricity always takes the path of least resistance.” What does that mean and what is the connection to our activity?

Optional:  Design and construct a paper circuit with multiple colored LEDs. As you learned, you will need to use more voltage than one coin cell battery so you can use your battery holder as a stand for your artwork or try to stack multiple coin cell batteries. Have fun by turning it into a piece of art. Consider mixed media with adding in the PlayDoh as your resistor.

Tips and Tricks:

  • Both the LED and coin cell battery have a Positive and Negative end. Notice the positive leg of the LED must connect with the positive side of the coin cell battery and same for the negative side.
  • Test your battery and LED to ensure your components work prior to assembly. Put the long leg of the LED to the top (+) side of the coin cell battery and the short leg of the LED to the bottoms (-) side of the coin cell battery. How many LEDs can the coin cell battery power in parallel? (add more LEDs to your test).
  • The copper tape will be your WIRE. It can just be ripped (you do not need to cut with scissors). It has adhesive on the back; just peel off the paper.
  • To get good connectivity you need pressure…make sure to press down on the LED legs and consider adding cooper tape both below and on top of the legs
  • Your coin cell battery acts like a switch. When you press on it, it closes the circuit.
  • You can stack your coin cell batteries to increase the voltage.
  • To keep your light on, tape it down.
  • LED legs can break off easily. Be mindful to not bend too sharply.
  • If using mixed media and adding in the PlayDoh. You may consider shortening the legs of your LEDs  (just cut with scissors) if combining.Will the PlayDoh replace the copper tape? Get creative and have fun.

Lesson Plan Translation

Downloadable Student Certificate of Completion