UV Light vs. Mold: The Ultimate Battle

Did you know that nearly 47% of all food produced in Canada, about 21 million metric tonnes, is wasted annually?

Did you know that over 41% of that food is edible food that is lost due to spoiling?

Our project is about how UV light reduces/inhibits mold growth. We chose this project to help find solutions to the real-world problem of food waste.

We researched about different types of UV lights, and deep into the science of mold.  We learned that UV lights with shorter wavelengths, such as UV-C light, are the most effective for reducing mold growth. This is because the shorter wavelengths are more powerful and carry high energy photons.

For our experiment, we prepared 12 agar filled petri dishes. 9 petri dishes were swabbed with mold samples for each of the 3 UV light types, and 3 petri dishes were for an experimental control (for no light exposure - in complete darkness) and observed the mold over the five day period.

After the five day period, we analyzed the data and found that UV-C light did reduce the most amount of mold growth!

We hope that our experiment can help promote food sustainability and reduce food waste!

Our project is about how different types of UV light such as UV-A, UV-B and UV-C reduce and inhibit mold growth. During the pandemic, it is our understanding that UV light was used to disinfect hospitals. The results and data from this experiment could determine what type of UV light to use in situations like these.

Our research question was: What type of UV light intensity (UVA, UVC, UVB) will inhibit/reduce mold growth (mm) in an agar rich petri dish over a time period of 4 days? We researched topics to deepen our understanding of mold such as mold and its characteristics and mold growth. We also learned about UV light wavelengths and its impact on mold growth. We learned that UV lights with shorter wavelengths (100-280 nm), such as UV-C light, are the most effective for reducing mold growth. This is because the shorter wavelengths are more powerful and carry high energy photons. These photons penetrate mold cells, damaging their genetic material (DNA/RNA) so they can't grow or reproduce.

Using this research we formed our hypothesis: If mold is surrounded by UV-C light then the molds surface area will reduce the most because UV-C light has the shortest wavelengths, and therefore a higher energy level, penetrating mold cells and stopping any mold cells from reproducing.

As mentioned earlier, our project could be used in many situations, such as reducing mold growth in your home, on your food, and potentially using this data to disinfect hospitals.

We conducted our background research through websites that were looked over and approved by our science teacher. We stayed away from sites such as Wikipedia that could be edited by the public. We research the topics: Indicators of dying mold, UV light wavelengths, Mold growth, and Mold and its characteristics.

We started our project by building aperatus to protect the mold from other natural light. Our objective was to test what type of UV light is best to inhibits/reduces mold growth. To start off our experiment, we prepared 4 boxes with holes designed to hang each type of UV light from (UV-A, UV-B and UV-C). 1 box was used for our control variable (no light). We then prepared 12 petri dishes with an agar base and swabbed mold from a food source onto them, and placed them into an oven set to 37°C for 2 days to allow the mold to grow. Then we put the petri dishes under the boxes. We placed 3 dishes under each type of UV light, UV-C, UV-B, UV-A and 3 dishes under a box with no light. We took pictures each day and made observations on the surface area and the characteristics of the mold.

The data collected from the experiment evidently shows an ongoing trend. The lights with shorter, stronger and more concentrated wavelengths like the UV-C light reduced the most mold growth while the lights with longer and less powerful wavelengths did not reduce the mold growth nearly as much. The lights with the shorter wavelengths carry high energy photons which ultimately penetrate mold cells and stop any reproduction of mold spores. Overall UV-C light reduced an average of 24% from day 1. Both

UV-A and UV-B lights only reduced a small amount, with the mold under the UV-A light averaging a 3.33% and the mold under the UV-B light averaging a 4.67% reduction. Aside from the data collected from the graph, there were also strong indicators that the mold under the UV-C light was dying. Over time the mold under the UV-C light started to become a pale white colour, while the rest of the trials stayed their original colour. This is a strong indicator that the mold cells have stopped reproducing, they can become brittle and change colour.

Some data that was unexpected in the end was that the mold under no light actually reduced more than the mold under the UV-A light. According to our research, this was unexpected because mold does grow best in darkness. Even though it did reduce more, it was only by a small amount. I think that if we had more trials and a more controlled environment, this would not have happened.

We collected our data by comparing the photos that we took over the 4 days and made hypothesis on how much the mold percentages had gone down. The results were mainly based on guessing but for some of the harder ones to analyze we used a graph and counted the amount of squares that were not filled with mold.

This experiment was created to test which types of UV light reduce the most amount of mold growth. It was hypothesized that if the mold was surrounded by UV-C light, the light with the shortest and most powerful wavelengths then the mold's surface area would reduce the most. The data fully supports the hypothesis with the mold under the light with the shortest wavelengths (UV-C) surface area reducing the most. Because UV-C light has the shortest wavelengths, and therefore a higher energy level, it will penetrate mold cells and stop any mold cells from reproducing. While the light with the shortest wavelengths did the most damage by a considerable amount proving our hypothesis correct, there was data that was collected that was unexpected.The mold under no light actually reduced more than the mold exposed to the UV-A light by a small difference of about 1%. According to our research, this was unexpected because mold typically grows best in dark conditions. Overall, the data and observations did fully support the hypothesis with the UV-C light reducing the most amount of mold growth.

During the process of spreading mold onto the petri dishes, the amount transferred was not always equal. This may have affected the starting amount of mold and its growth rate. To reduce this error, the number of swabs should be controlled. Also, the boxes used to hold the lights were not always the same height, which could change light distance. Measuring each box height would increase the accuracy of the data.

A possible extension would be testing other factors that affect mold growth, such as temperature, and repeating the experiment in a more controlled environment.

Two of our teachers, Ms. Rose and Mr. Hodgins helped an incredible amount when souring the materials for our experiment and helping to conduct our experiment safely and correctly. Mr. Hodgins, as well as providing guidance in our project, also provided us with the mold from a food source to conduct our experiment with. Ms. Rose found and ordered all of our UV lights and helped prepare the agar filled petri dishes for our experiment. She made sure we were using the correct safety protocols when dealing with the mold.

WORK CITED:

“Does UV Light Kill Bacteria and Mold?” Lennox.com, 2025,

www.lennox.com/residential/lennox-life/air-quality-issues/does-uv-light-kill-bacteria-and-mold.

“Mold | National Institute of Environmental Health Sciences.” National Institute of Environmental Health Sciences, https://www.niehs.nih.gov/health/topics/agents/mold. Accessed 23 January 2026.

“What are Molds? - North Central District Health Department.” NCDHD-CT, https://www.ncdhd.org/what-are-molds. Accessed 27 January 2026.

“Effect of colour LEDs on mycelia growth of Aspergillus ficuum and phytase production in photo-fermentations.” Pub-Med, Springer, 2012, https://pubmed.ncbi.nlm.nih.gov/22082775/. Accessed 27 January 2026.

Mack, Yazmin. “Exploring the impact of light wavelength on indoor mould growth.” Frontiers, 1 June 2025, https://www.frontiersin.org/journals/built-environment/articles/10.3389/fbuil.2025.1602552/ful Accessed 21 February 2026.