How does light intensity change with distance?

If the brightness of light intensifies at the light source, then the brightness should get dimmer at a distance.

● Bulb socket with cord;

● Three different light bulbs with different wattage; two are 40 watts - standard and one is 60 watts - LED;

● 60 inch (152 cm) Measuring tape;

● Graph paper;

● Google Science Journal Application downloaded on Smart Phone to measure and record data:

● Material to align Smart Phone with the light source. This could be a ball of clay, an easel or a camera stand. I'm choosing an easel.

● Room that can be darkened well and cleared of objects in a 6-foot by 6-foot area.

● Notebook to write down all my data.

1. Gather all materials;

2. Familiarized myself with the Science Journal App. They explained how to find the exact location of the light sensor on my Smart Phone and how to take light intensity readings.;

3. Choosing my light source: In this step, I chose three light bulbs to test. Light Bulb 1 is 40 watts - standard, incandescent, with a clear glass bulb; Light Bulb 2 is also incandescent with clear glass but is 60 watts - LED. Light Bulb 3 is also incandescent and 40 watts - standard with a frosted glass.;

4. Finding a place to take measurements: A) I had to find an area that is approximately 6 - feet by 6 - feet. The room has to be darkened in order to be able to get the proper light source reading; B) I had to remove any shiny items that can reflect light and alter the result of my test; and C) I have to be as far as possible from walls that could reflect any light.;

5. Set up the light source: In this step, I propped up my bulb socket with light bulb onto my easel, secured the measuring tape (this is to measure the distance between the light source and the light sensor on the Smart Phone) and propped up the Smart Phone to capture the proper light intensity reading.;

6. Make sure that the light sensor on the phone is the same height as the light source to get the proper reading.;

7. The Smart Phone has to glide, in a controlled way, towards and away from the light source to be able to get the light reading.;

8. Create a table in the Notebook (Table 1) - this table will record the measured light intensity for different distances from the light source.;

9. Darken the room that will be used to perform the experiment.;

10. Turn on the light bulb and wait a few minutes for the bulb to reach its maximum brightness.;

11. Start by holding the sensor (Smart Phone) relatively close to the bulb, at 10.5 cm distance.

12. Move the Smart Phone away from the light source and determine a distance where the measurement is very low and the changes are minimal with changing distance. This is the starting point.;

13. Measure and record a single data point at each distance. This is done with the Science Journal App.:

A. Hold the Smart Phone at the starting distance;

B. Write down the distance in the Notebook, read the lux measurement, which is the measure of how much visible light is present, and the illuminance as a measure of the intensity of illumination on a surface. Record the value in Light Intensity Measurement Table.

C. Move the Smart Phone 5cm closer to the light source and repeat step B. Continue this until the light sensor is very close to the light source. The measurements of light intensity were measured at a distance of 5cm, 15cm and 25 cm.

14. Repeat Number 13 two more times for a total of three test trials.

Dependent Variable - Intensity of the bulb

Independent Variable - Light Bulbs

Constant - Smart Phone

Darkened room

Measuring tape

Easel

Light bulb socket

Control (if applicable) - None

How does light intensity change with distance? My hypothesis was that if the brightness of the light intensifies at the light source, then the brightness should get dimmer at a distance. I based my hypothesis on the idea that the closer an object is to the point of source, the brighter it is, and the further away the object is the dimmer it gets. Based on my findings, this stands to be correct. The measure of intensity of the light at the point of source is brighter, and, as the experiment progressed, the data showed that the further away the light sensor was from the point of source, the measure of light intensity became dimmer.

Have you ever looked up at the stars at night and wondered how fast they were moving or how far away they were? By studying how the brightness of a star changes with distance, I am able to answer those questions. In this astronomy science project, I created a model of starlight to determine how the light intensity of a point source of light, like a star, changes with distance from that source. I was able to find the relationship between brightness and distance .

How does light intensity change with distance? If the brightness of the light intensifies at the light source, then the brightness should get dimmer at a distance. Based on my findings, this stands to be correct. After conducting my experiment three times, with the three light bulbs chosen, at a distance from the light source of 5 cm, 15cm and 25 cm, I was able to conclude that the light intensity or lux at the point source is brighter. As I continued to conduct the experiment, moving the light sensor away from the point source, the measure of intensity became dimmer. The data will show that although there are fluctuations in the measure of intensity of the light between Test 1, Test 2 and Test 3, that the intensity did decrease as the distance from the source grew. This is a constant that always remained during the entire experiment. The average light intensity (lux) for Light Bulb 1 - at 5cm distance was 28.8 lux; at 15 cm distance 12.8 lux; at a 25cm distance 8.4 lux. Light Bulb 2 - at 5cm distance was 65 lux; at 15cm distance 40 lux; at 25 cm distance 30.7 lux. Light Bulb 3 - at 5cm distance was 20.4 lux; 15cm distance 14.1 lux; 25cm distance 10.8 lux.

I did find something curious between the three light bulbs I used for my experiment. Although the light bulbs I used proved my hypothesis, I noticed that my first light bulb, Light Bulb 1 which was a Clear Glass 40 Watt - Standard Bulb, the bulb got very hot. In Light Bulb 3 - the Frosted White 40 Watt - Standard Bulb, the bulb got equally hot. In Light Bulb 2 - the Clear Glass 60 Watt - LED Bulb, the bulb was not hot and the light intensity readings were much higher than that of Light Bulbs 1 and 3. These factors did not impact the result of my experiment but perhaps it could help in the determination of which light bulb would be most efficient for someone's home.

In conclusion, the brightness of light does intensify at the light source and does get dimmer as it moves further away from the point source. Therefore, the brightness of light does change with distance.

In the process of conducting this experiment, I found that out of the three light bulbs that I have used, one of the light bulbs could be the most efficient to use in your home. This light bulb would be Light Bulb 2 - the clear glass 60 Watt - LED bulb. The bulb did not get hot during the experiment and the light intensity readings were much higher than that of Light Bulb 1 and Light Bulb 3.

“Star light, Star bright: How Does Light Intensity Change with Distance?” Science Buddies, 23 June 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Astro_p034/astronomy/how-does-light-intensity-change-with-distance.

Arduino Science Journal App: https://www.arduino.cc. education/science-journal

Astronomy: The Sky and The Solar System - The Distance to and Brightnesses of Stars:https://courses.lumenlearning.com/towson-astronomy-2/chapter/the-brightness-of-stars

Acknowledgements