1. Light Energy
NATURE Sunday Academy

2. Light and Energy Why do cats lay in the sun?
In large part because they enjoy collecting the energy in the light.
Light is a form of energy called “solar energy”.

3. Activity 1 Find Activity 1 on page 1.
We will see how the brightness of light is affected by distance from the light source.
Depending on your classroom, you may use either a flashlight or an overhead projector as your light source. If you use the flashlight, you will need to use the instructions for a circular image

4. Activity 1 (continued)
Measure the distance between your light source and the wall (in metric units)
2 of your distances should be at 1m and 2m
Use the data table in your lab
Trace out the image as you move back
Measure the area of the image
You will be making a graph with distance on the x-axis and area on the y-axis

5. Activity 1 Discussion
Is the graph you made a straight line or a curved line?
How would you put into words the relationship between the area lit up and the distance from the screen?
How does area approximate light intensity?
Should be a curved line…like half of a parabola
The rate at which the area increases is the square of the distance from the screen (they might say that the area increases more quickly the further you get from the screen).
The greater the area, the less intense the light.

6. Activity 1 Discussion
This graph shows actual light intensity versus distance from source, an actual inverse square law.
How would you describe the way that light intensity drops off with distance?
How might you collect data that would create this graph?
The further you are from the light source, the less intense the light.
Students will probably suggest using an actual light sensor. Alternatively, they might suggest putting the inverse of the area on the y-axis.

7. Activity 2 Find Activity 2 on page 3
This activity will illustrate why light becomes less intense as you move away from the source.
Do Activity 2 now. (You do not need to cut out the circles)

8. Activity 2 Discussion
What happened to the distances between the pennies (represent photons) as the circle got bigger?
Why do you think the model did not change the number of pennies as you changed the size of the circle?
As the circles got bigger, the pennies were more spread out.
Because light is made of photons and as a light source is further and further away, the photons are more spread out. No more are added.

9. Activity 3 Find Activity 3 on page 4
Now that we have some idea how light intensity and distance from source are related, we will compare light intensity from different sources.

10. Activity 3 continued Construct a null-photometer Video (see notes)
The video I made on how to do this evaporated. But you can find the actual video in the Activity 3 bubble of the Prezi at:

11. Activity 3 Discussion
Do incandescent bulbs and CFL bulbs have the same light intensity at the same distance from the source?
Why might many people prefer to use the CFL bulbs (what is their advantage)?
What measurement system did we come up with for intensity?
What might be a limitation of this system?
Not quite; the CFL has slightly lower intensity (note: this may vary based on manufacturer)
CFL bulbs are a lot more efficient: you get more light for the electrical power used.
We used a relative measurement for intensity: how does the intensity compare to a 60 W incandescent bulb?
There are many limitations: it is a subjective judgment (eyeball) rather than a machine. Also, the light may not be the same color. Outside light might interfere with the results.

12. Activity 4 Find Activity 4 on page 6
In this activity we look at the amount of energy we can collect from sunlight (solar power)
Note that everything in this activity is estimation.
Definition: wattage is the amount of energy delivered per second

13. Activity 4 Discussion
The sun delivers 1380 W of energy per square meter.
Each day is half sunlight and half darkness which leaves:
690 W per square meter
Since the day is not fully sunlit, we are left with
345 W per square meter

14. Activity 4 Discussion The atmosphere is dusty which leaves
173 W per square meter
Solar panels only collect about 20% of the energy that hits them. This leaves
35 W per square meter
An average house uses 2100 Watts of power.
60 solar panels are required

15. Activity 4 Discussion
Some possible limitations: do you have enough roof on your house?
The author’s house is 645 square feet
The author’s house is well shaded by trees
The author’s house has a roof that slopes east and west (not south)
An example of a solar powered house

16. Activity 5 Find Activity 5 on page 7
This final activity will illustrate how light energy can be turned into electrical energy
Our indicator will be the tinsel. As electrons are kicked out of the metal, they will move to the tinsel, causing the tinsel to repel (which you will see as fluttering)

17. Activity 5 Discussion
Why does the tinsel repel when it has extra electrons in it?
How do you know UV light is required to kick out the electrons?
The electrons are negatively charged and like charges repel. Since the parts of the tinsel all have negative charges, they repel each other.
Unless something strange is going on, there should only have been tinsel repelling if there was UV light.

18. Wrap Up Light is energy We can convert that energy to electricity
This will not solve our energy problems due to practical considerations (but it will help)
Efficient bulbs convert more energy to light than to heat
Light intensity drops rapidly as you move away from the source

19. Activity 6 - Seasons Seasons are caused by Earth’s tilt
Greater angle spreads the sun’s energy out more
Short video at:
Image from