Angle of Incidence


How will the angle of incidence effect a light's intensity?


lab diagramThe more directly the sun's rays strike the Earth the greater the heat energy received. Lower latitude locations (closer to the equator) get more heat energy and are warmer. We will use an LED to create an analogy for sunlight striking the Earth's surface.


If the angle of incidence is ______ then the light intensity will be ______ because _______.


  1. Set up the apparatus as shown in the diagram. The height of the LED should be constant for both angles (45° and 90°).
  2. Using the grid on the back of this paper, trace a line around the ellipse of light created by the LED (sun) when the rays are striking at a 45° angle to the graph paper (Earth's surface).
  3. Next to the first ellipse you traced, draw another ellipse using the LED that is set perpendicular to the graph paper.
  4. Calculate the surface area illuminated in both situations by counting the number of boxes within each ellipse. Write the numbers in table 1.
  5. Assuming the light energy from each LED is identical (1000 milliwatts), calculate the energy per box for the two ellipses and enter these numbers in Table 1.
    Use this formula:       energy per box = 1000 mW / number of boxes
    Table 1 45 ° 90 ° (Perpendicular)
    Boxes illuminated  

    Energy per box  
  6. On the back of this paper, sketch the Sun - Earth system illustrating the sun's rays striking the earth directly and at the polar regions.


Use your data and the diagrams to explain why low latitudes are warmer climates than higher latitudes.