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Don't Get Burned! Measure the UV Index at Different Times of the Day

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It's true that the light from the Sun provides the heat and light we need to survive here on Earth, but it also poses a threat. Ultraviolet (UV) rays in sunlight cause damage that can lead to early skin aging and even skin cancer. In this science fair project, find out when you need the most protection from UV rays by using a personal UV monitor to measure how the level of ultraviolet light changes during different parts of the day.


Areas of Science
Time Required
Short (2-5 days)
Material Availability
You will need to order a personal UV monitor online. Please see the Materials and Equipment list for details.
Low ($20 - $50)
Do not look at the Sun when you are measuring the UV level. Wear sunscreen when you are in the sunlight.

David B. Whyte, PhD, Science Buddies


Measure the change in UV levels over the course of a day.


Comedian Robin Williams once said, "Spring is nature's way of saying, 'Let's party!'". The arrival of spring brings the return of the warmth and light that were in short supply during the winter months. We go to sunny beaches, have picnics, play in the park. But do you try to avoid getting too much Sun exposure? There is a good reason why you should: sunburns! While most of the ultraviolet (UV) light that is produced by the Sun is filtered out by the atmosphere, enough UV light reaches Earth to cause damage to the DNA in the skin cells of unprotected beach-goers. DNA is like a set of instructions that is stored in almost every cell of your body (red blood cells do not have DNA). When you get a sunburn, the DNA is damaged. The damage can cause some of the instructions to change change or be lost, which is not a good thing. DNA damage in skin cells can sometimes lead to skin cancer. UV light can also damage the eyes, contributing to the development of cataracts later in life.

The level of UV light increases during the morning and then peaks at midday. But how does it change? Is the amount of UV light at 10:00 AM 50 percent of what it will be at noon, or perhaps it is 25 percent? In this science fair project, you will determine how the level of ultraviolet light changes during the course of a day, using a personal UV monitor. The monitor has a scale for the UV index that goes from 0 (no UV) to 25 (extreme UV exposure). Once you have measured the amount of UV light at different times during the day, you will graph your results so you can see how the UV light changes over time. After you do this science fair project, you can still enjoy the sunlight on a nice spring or summer day, but you'll know more about how to protect yourself from too much of a good thing!

Terms and Concepts



  • Kids Health. (2009). Sun Safety. Retrieved September 17, 2009.
  • NASA. (n.d.). Ultraviolet Waves. Retrieved September 17, 2009.
  • United States Environmental Protection Agency. (2009). UV Index for Kids. Retrieved December 7, 2009.

For help creating graphs, try this website:

  • National Center for Education Statistics. (n.d.). Create a Graph. Retrieved December 2, 2009.

Materials and Equipment

Disclaimer: Science Buddies participates in affiliate programs with Home Science Tools, Amazon.com, Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity, and keep our resources free for everyone. Our top priority is student learning. If you have any comments (positive or negative) related to purchases you've made for science projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

Experimental Procedure

Before you begin the procedure, read the directions that came with the UV monitor.

  1. Choose a spot that is outdoors and that gets direct sunlight all day long.
  2. Measure the UV index using the UV monitor early in the morning. Try to get the first reading soon after sunrise.
A portable UV monitor that has a reading from 0 to 15Image Credit: Svenja Lohner, Science Buddies / Science Buddies
Figure 1. A portable UV monitor. The monitor has a UV-sensitive sensor and provides a reading of the UV index from 0 (no UV) to 15 (extremely high UV).
  1. Since you will average your reading over three days, try to perform the tests on days that have similar conditions. For example, choose three sunny days for the tests, if possible.
  2. Press and hold the ON/TEST/OFF button for two seconds to turn the device on.
  3. Point the UV sensor of the UV meter directly at the sun. The sensor is embedded inside the transparent knob on top of the device.
  4. In the standby mode, press the ON/TEST/OFF key once, to take a measurement of the UV irradiance. The measurement takes one second.
  5. The UV irradiance and UV index will be displayed for about 15 seconds. The UV meter will go back to the standby mode again if the ON/TEST/OFF key is not pressed.
  6. Record the date, time, location, and UV index number in a data table in your lab notebook, like the one below.
    1. For location, write down the city from where you take your readings.
    2. Add a column for notes, such as "cloudy," "hazy," etc.
Day 1
DateTime LocationUV Index 1 UV Index 2 UV Index 3 UV Index Average Notes
  1. Take two more readings right away so that you have three separate readings for this same time.
  2. Repeat the procedure every hour until sunset. You might want to use a timer so you don't forget when it's been exactly an hour.
  3. Repeat the entire procedure on at least two more days. This will show that your results are accurate and repeatable. Choose days that are sunny.
  4. Now graph the data. You can use graph paper, or graph it online at a website such as Create a Graph.
    1. Calculate the average UV index for each time and record the averages in the data table. To calculate the average, add the three UV index numbers for each time together, then divide by three. Have an adult help you with this step, if necessary.
    2. Graph the UV index on the y-axis and the time on the x-axis.
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Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

Global Connections

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.

This project explores topics key to Good Health and Well-Being: Ensure healthy lives and promote well-being for all at all ages.


  • Compare the UV index on cloudy vs. sunny days.
  • Compare the UV index in a shady area vs. a sunny area.
  • Keep the monitor horizontal for each reading. How does this affect the amount of UV striking the monitor?
  • Graph your data as percent maximum UV index vs. time. Use 100% for the highest UV index, and calculate the other values as percentages of the maximum. At what time in the morning is the UV index at half maximum?
  • Investigate how the UV index changes during different seasons.


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General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Science Buddies Staff. "Don't Get Burned! Measure the UV Index at Different Times of the Day." Science Buddies, 23 June 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/HumBio_p028/human-biology-health/uv-index-at-different-times-of-the-day. Accessed 21 Apr. 2024.

APA Style

Science Buddies Staff. (2020, June 23). Don't Get Burned! Measure the UV Index at Different Times of the Day. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/HumBio_p028/human-biology-health/uv-index-at-different-times-of-the-day

Last edit date: 2020-06-23
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