lesson 2: Power-Brightness Relationship of LEDs
PREPARATION
Digital Wattmeter Module
This is an I2C digital power meter with a Gravity interface. It can measure the operating current, voltage, and power of various sensors and actuators.
In this lesson, students will gain insight into the power of various electrical appliances. They will develop the skills to measure and analyze the power of these appliances. Students will learn how to implement simple energy-saving control mechanisms for small lights.
ENGAGE
What is power?
Power in electricity is the rate of energy transfer or consumption, measured in watts (W). It shows how much work an electrical device can do per unit of time.
Simply put, the higher the power, the more energy the device uses per unit of time.
Here is a diagram that can illustrate how many watts each type of appliance typically uses.
Guiding students to understand the basic relationship between current, voltage, and power.
Current and voltage lead to power.
To predict the brightness of bulbs you need to think about the power in the electrical pathway. The brightness is the result of two electrical factors:
The flow – that is the current
The push – that is the voltage
Assuming an ammeter connected to the circuit indicates a current of 2 amperes, we can deduce that the current flowing through the bulb is also 2 amperes. This means that 2 coulombs of charge pass through the bulb each second. Given that 12 joules of energy are transferred to the surroundings for every coulomb of charge passing through the bulb, we can calculate that the bulb transfers 24 joules of energy each second (since 2 coulombs/second * 12 joules/coulomb = 24 joules/second). Therefore, the power of the bulb is 24 watts
EXPLORE
Separate students into several groups for a modified jigsaw activity using the following resources.
Student-lead summarization:
Within their jigsaw groups, students should construct an explanation for the following question: “Which bulb consumes the most energy and which is the most energy-saving?” Each group should answer this question by rating the power consumption of these four types of bulbs and then share their findings with the whole class.
EXPLAIN
From the data in the table, LED lighting provides the maximum benefits across all areas - energy efficiency and lifespan. Although LED lights have a higher upfront cost compared to incandescent and halogen bulbs, considering the overall cost, they save money in the long run.
LEDs and CFLs result in lower greenhouse gas emissions from power plants. If everyone switched to efficient lighting, the pollution reduction would be significant.
Therefore, the colorful LED might be a reasonable lighting device for a power station.
After sharing and drawing conclusions, encourage students to consider “what the relationship is between the brightness of LEDs and their power”.
CHALLENGE
Follow the instructions to explore the relationship between the brightness of LEDs and their power.
Step 1: Import user library
Open Mind+ and Click Extensions
Select User-Ext->Type “power meter”>Press “Enter”
Choose Power(EDU)->Click “Yes”
Back to coding page
Step 3: Calibrate power meter
Connect the power meter to the I2C pins of Unihiker K10 (SDA/SCL).
Complete the code and upload it to Unihiker K10. Then, in the terminal, select 'Open Serial'.
Now that we have the no-load calibration value, we need to enter it in the correct position to ensure more accurate measurements.
Provide students with two challenges to develop their knowledge of power consumption. These challenges are themed around exploring the power consumption of LED. It should be noted that these challenges need to be carried out in sequence.
Challenge 1
Determine the power consumption of the LED strip.
Firstly, connect the hardware according to the diagrams provided below.
Secondly, turn on the LED strip. The power meter module is equipped with control functionality, allowing us to control the actuator's switch by manipulating the corresponding pins.
Thirdly, guide students to complete the following program.
Finally, downloading and the power of LED strip is showing on the screen.
After measuring the LED power, proceed to explore how brightness affects power consumption.
Challenge 2
Explore the relationship between the brightness of LED and its power consumption.
First of all, creating a brightness-controlled LED strip using buttons A and B. How to accomplish this function? What you need to do is to make a variable named “brightness” and program it to increase or decrease in response to pressing buttons A or B.
Here are the steps you can follow:
Make a new variable named brightness.
Increase brightness by 100 when button A has been pressed.
Combine variable “brightness” and analog output together.
Finish the complete program as below.
After downloading this program, you can adjust the brightness of the LED strip by using buttons A and B.
Next, integrate the power measurement function into the program and show the brightness and power on the screen.
Below is the code example.
From the effects shown above, it can be observed that the light strip in the left image has a lower brightness and correspondingly lower power. In contrast, the light strip in the right image is brighter and has a higher power.
Within their jigsaw groups, students are tasked with filling out the table provided below and subsequently creating a line chart to vividly illustrate the correlation between brightness and power.
CONCLUSION
The teacher will now summarize the lesson and guide the students to disconnect and neatly pack away all equipment before returning it.
Program-L2.zip 
