The Effect of Distance on the Light Intensity from Different Sources

Student: Claire Liang
Table: 7
Experimentation location: Home
Regulated Research (Form 1c): No
Project continuation (Form 7): No



Works Cited

Admin, L., & Admin, L. (2023, September 30). What are lumens? Lumens Chart & Light Bulb Facts | Lumens. The Edit: The Lumens Content Library - Inspiration, news and advice from the design experts at Lumens. 

Ask an Astronomer. (n.d.). Cool Cosmos.,27%2C000%2C000%20Fahrenheit%20(15%2C000%2C000%20Celsius)

Divilife. (2022). How to measure light intensity. BIOS Lighting.,that%20they%20indicate%20lumen%20output

EarthSky. (2022, November 5). EarthSky | Do plants grow as well under artificial light? EarthSky | Updates on Your Cosmos and World.,light%20spectrum%20as%20sunlight%20does

Engineering, O. (2021b). How Bright is it? Shining a light on intensity measurement.

Light Intensity definition | Psychology Glossary | (n.d.).,at%20a%20unit%20of%20surface

Staff, W. (2018, January 19). What is the difference between lux and lumens? 

Additional Project Information

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Research Plan:

I. Introduction

Visible light is the small portion of the electromagnetic spectrum between ultraviolet waves (UV waves) and infrared waves (heat waves) (Engineering para. 2). Different wavelengths of light are interpreted by the human eye as the different colors, such as red, orange, yellow, green, blue, and violet (Engineering para. 3). Artificial light (any man-made light) only emits some wavelengths of light (EarthSky para. 2). The sun emits all the colors of the spectrum which produces white light, and radiates much more energy than any light bulb (EarthSky para. 2). In fact, the sun is so powerful that its surface temperature is 5,600 degrees Celsius (Astronomer para. 1). To put this into perspective, the temperature of boiling water is 100 degrees Celsius. The fact that living creatures on Earth are not burned by the sunlight indicates that the light intensity must have decreased with the distance. In this experiment, I will investigate how light intensity varies with distance using a number of different light sources.

Light is measured in lumens and lux (Admin para. 2) (Divilife para. 8). Lumens are the unit of measurement for the amount of light emitted from an energy source (Admin para. 2). Lux is the unit of measurement for the number of lumens that land on a square meter (Divilife para. 8). The bigger the space that needs to be lit up, the less light falls on a surface, which is light intensity (Light Intensity para. 1). With most light sources, the amount of lux will decrease with distance because the farther something is, the more the light disperses, therefore decreasing the lux reading (Staff). In this project, the light intensities of a candle, a light bulb, and a diode laser will be measured at different distances by a lux meter app.

II. Materials

  • A light bulb
  • A candle
  • A diode laser
  • A lux meter
  • A meter stick/measuring tape

           III. Procedure

  1. Place the candle on a flat surface, keeping it in place and making sure the light faces up. 
  2. Place the detector at 5 centimeters above the light source, facing the candle. 
  3. Get a lux measurement.
  4. Repeat steps 2 and 3 two more times. These are the replicates of the experiment.
  5. Do steps 2 through 4 at the 10, 15, 20, 25, and 30 centimeter distances.
  6. Place the light bulb on a flat surface, keeping it in place and making sure the light faces up. 
  7. Place the detector at 5 cm above the light, facing the light bulb. 
  8. Get a lux measurement.
  9. Repeat steps 7 and 8 two more times. These are the replicates of the experiment.
  10. Do steps 7 through 9 at the 10, 15, 20, 25, 30, 40, 60, 80, 100, and 120 centimeter distances.
  11. Place the laser on a flat surface, keeping it in place and making sure the light points horizontally. 
  12. Place the detector at 1.5 meters from the laser. The lux detector should be at the same height as the laser.
  13. Get a lux measurement.
  14. Repeat steps 12 through 13 two more times. These are the replicates of the experiment.
  15. Do steps 12 through 14 at 3, 4.5, 6, 7.5, 9, 10.5, 12, 13.5, and 15 meter distances.

IV. Safety Precautions

  • Do not shine the light in someone’s face/eyes, especially the laser. It may lead to blindness or permanent damage.
  • Be careful when handling the candle otherwise you might burn yourself with the wax.


Questions and Answers

No additional information provided.