| Complexity level: | 9 |
| Project cost ($): | 60 |
| Time required: | 1 hour to prepare, 1 day for the science project experiment |
| Material availability: | Easily found |
| Safety concerns: | Avoid long exposure to strong sunlight. Wear protective clothing and eyewear. |
Hypothesis
Light colored clothing will provide better protection from UV light.
Overview
Ultraviolet radiation
Ultraviolet (UV) radiation is part of the electromagnetic spectrum of light that travels to earth from the sun. In the spectrum, it falls between visible light and X-rays. UV light falls at the blue end of the light spectrum and cannot be seen by the naked eye. It contains a higher energy level and shorter wavelength compared to visible light. Based on its effect on living organisms, UV light is classified in three categories - namely UVA, UVB and UVC.
- UVA with a wavelength of between 315nm and 400nm is capable of penetrating our skin and accelerate skin aging. Our skin is able to tolerate normal levels of UVA radiation.
- UVB with a wavelength of between 280nm and 315nm does not penetrate very deep into our skin, but carries a higher amount energy. Only a small amount of UVB is able to penetrate the ozone layer and reach the earth surface. UVB causes a burning sensation when in contact directly with the skin.
- UVC with a wavelength of between 240nm and 280nm has even higher amounts of energy but it is immediately lost upon contact with a surface. UVC is the most harmful type of UV light to all living organisms including humans. It is used to kill microbes in germicidal applications. Almost all of the UVC from the sun, is prevented from reaching the earth's surface by our atmosphere.
UV levels are normally at their highest around 10:00 am to 2:00 pm everyday. One of the most convenient ways of measuring UV levels is the UV index. Each unit of the UV index represents about 25mW per square meter of UV radiation. The UV index is a very useful way of providing information to the public regarding daily UV exposure levels
The UV index range is described as follows:
Less than 3: Moderate levels
Between 3 and 6: High levels - enough to cause sunburn even at temperatures below 27 degrees Celsius
Between 7 and 9: Very high levels - enough to cause sunburn on cloudy days
More than 9: Extreme levels - that cause sunburn to an unprotected skin within 12 minutes.
Scientific Terms
Materials
The materials required for the science fair project experiment:
- 1 black cotton cloth
- 1 blue cotton cloth
- 1 red cotton cloth
- 1 white cotton cloth
- 1 UV meter to measure UV index
- 1 glass aquarium
Procedure
1. For this science fair project, the independent variable is the color of the cotton cloth used to block the UV radiation – black, blue, red and white. The dependent variable is the level UV radiation measured. This is determined by using the UV meter. The constants (control variables) are the time the measurements are taken, the level of sunlight on the testing day and the geological location where the testing is done.
2. The empty glass aquarium is placed under direct sunlight at around noon, away from any shadows. The UV meter is placed inside the glass aquarium and the reading on the UV meter is taken. The reading is recorded in the table given below.
3. The black color cotton cloth is placed over the open top of the aquarium. The new reading on the UV meter is taken and recorded in the table given below.
4. The black cloth is removed from the glass aquarium and the UV meter reading is checked once more to confirm if the UV levels are still the same. The blue color cotton cloth is next used to cover the UV meter and the new reading on the UV meter is taken again..
5. Procedure 5 is repeated using the red and white colored cotton cloth. All readings are recorded in the table below.
Results
It is observed that the black and blue cloth were effective at blocking off most UV radiation while the white cloth was the least effective at doing so.
| Cloth color | UV index level | |
| Outside box | Inside Box | |
| Black cloth | 6 | 2 |
| Blue cloth | 6 | 2 |
| Red cloth | 6 | 3 |
| White cloth | 6 | 5 |
Conclusion
Our hypothesis that dark colored clothing provide better protection from UV light is proven to be false.
UV light is used with security devices like the smart chips on our credit cards and passports, for identifying marks that are only visible under UV lighting. In criminal forensics, UV light is used to locate body fluids in crime scenes. UV light is also useful in waste-water treatments and for killing microbes in our drinking water.
Also consider
What would happen if the science fair project was repeated using different types of clothing like nylon or polyester?
The science fair project can be also repeated by using other colored clothing like grey, green, white, etc.
References
About forecasts for UV protection - http://www.bom.gov.au/info/about_uv.shtml
Why measure UV? - http://www.solatell.com/Why%20measure%20UV.htm
How to measure the UV index using the UV meter? - http://www.bom.gov.au/info/weatherkit/section2/pdf/uv.pdf
