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Do different LED colours behave alike?
Compare three LED colours using the same resistor and two supply settings.
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Learning Outcomes
Compare electrical readings from three LED colours under matched nominal conditions.
Estimate LED voltage from supply setting and measured resistor voltage, stating the limitation.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
Same supply, different colours
5 min
A panel can use red, yellow and green indicators connected to the same power supply. Does sharing the supply mean the LEDs carry the same current? Investigate each colour with a 1 kΩ resistor at 3 V and 5 V. Let the meter, not a photograph’s brightness, decide the electrical comparison.
Predict whether all three colours will carry the same current at 3 V. State your reason without assuming a colour ranking.
Make a fair comparison
25 min
Read the circuit
The lab button opens a wired circuit on real equipment. A branch is one path containing a resistor and an LED. The LED has an anode (A) and cathode (K); their orientation is already set. Select the DC Power tab to read or change the positive supply setting; select Multimeter to read the voltage. Click Perform Measurement after every change and wait for the result and rack photographs to refresh. Changing a setting alone does not produce a new result. To adjust voltage with the keyboard, focus the voltage knob: Left/Right changes the step; Up/Down changes the value. Check the displayed voltage before measuring.
The multimeter reads the voltage across the resistor, called $V_R$. Record VDC in volts; divide an mV reading by 1,000. For example, 240 mV = 0.240 V. If the display shows uV (microvolts, µV), divide by 1,000,000: 300 uV = 0.000300 V. For a 1 kΩ resistor, $I\,\text{(mA)}=V_R\,\text{(V)}$. This calculates current from measured voltage and the stated resistance.
Use the camera photographs for observations of the real lights. The drawing’s Estimated glow is an illustration of the last result, not a light measurement; turn it off during camera comparisons. A light hidden by glare is unclear, not necessarily off. The rack also contains status lights. If the circuit LED is unclear, keep the same circuit and voltage and press Perform measurement again. Wait for the result and camera photographs to refresh, then inspect the LED again. Briefly note the first and repeat readings and any change in visibility in your written answers; use the repeat result in the table. If the LED is still unclear, choose Unclear; do not judge it from another light or keep repeating until you obtain the answer you expected.
Read the equipment name shown under each result: successive measurements can use different physical Hives. Small differences may therefore reflect different components. A result labelled as a previous recording is not an independent new measurement.
Keep the circuit protected
Keep the supplied wiring and resistors in place. Use only the positive 0–5 V supply, between 1 and 5 V in this activity. Do not connect an LED directly to the supply. Leave the other supplies and function generator unchanged. The meter is already connected across a resistor: leave it in DC voltage mode, never current or resistance mode.
Read the voltage across the resistor to calculate the current through that branch. A and K identify the LED terminals.
Changing circuits
When you finish a circuit, use Leave now in Hive, then return to this activity before opening the next lab button. Each button loads its own circuit; do not reuse a previous circuit or rewire the meter.
Red
Red
Open the circuit; change the positive supply from its initial 5 V to 3 V. Measure and fill the Red, 3 V row. Change to 5 V, measure and fill the Red, 5 V row. Keep its 1 kΩ resistor and meter connections unchanged.
Available in a class session
Green
Green
Open the circuit; change the positive supply from its initial 5 V to 3 V. Measure and fill the Green, 3 V row. Change to 5 V, measure and fill the Green, 5 V row. Keep its 1 kΩ resistor and meter connections unchanged.
Available in a class session
Yellow
Yellow
Open the circuit; change the positive supply from its initial 5 V to 3 V. Measure and fill the Yellow, 3 V row. Change to 5 V, measure and fill the Yellow, 5 V row. Keep its 1 kΩ resistor and meter connections unchanged.
Available in a class session
Results
Complete six rows: 3 V then 5 V for each colour. Record measured V_R, calculate I(mA)=V_R(V), then estimate V_LED = supply setting − V_R. This LED voltage is an estimate because the supply setting is not a separate voltage measurement. Choose a camera observation and leave extra rows blank.
| LED colour | Supply setting V | Resistor voltage V | Calculated current mA | Estimated LED voltage V | Camera observation |
|---|---|---|---|---|---|
What does colour tell us?
15 min
Use the green LED at 5 V. Give its estimated LED voltage in V and show your subtraction using the measured resistor voltage.
At 3 V, were the three currents clearly different or too close to distinguish confidently? Cite your readings. Then check whether the 5 V readings support the same conclusion.
Why should your estimated LED voltages not be reported as exact constants for every red, yellow or green LED?
A designer wants equal currents through three differently coloured indicators. Is using identical resistors enough to guarantee that? Answer using your evidence.
Submit
After all measurements, leave Hive and return here. Mark the lab practice as done, check every results row and required answer, then submit the activity.
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