Introduction: (Initial Observation)
Invisible UV (ultraviolet) radiations from sun or other sources can cause sunburn, skin cancer and damage to the eyes. It is important for us to detect the presence and strength of UV lights so that we can minimize our exposure or protect ourselves by using UV filtering eyeglasses and sunscreen lotions.
The main problem with the UV light is that it is invisible, so it quietly burns the skin and damages the eyes and we will only notice its harmful effects, when it is already too late. Fortunately there are materials that can easily detect UV light and give us advanced warning. One of such materials is known as UV sensitive beads. Girls use them to make bracelet and they enjoy the vibrant colors they radiate under sunlight. In this project you will use UV sensitive beads in your experiments.
Find out about the invisible UV radiation. Read books, magazines or ask professionals who might know in order to learn about different effects of UV radiation. Keep track of where you got your information from.
Following are samples of information you may find:
What is UV Light?
Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays. It is named because the spectrum consists of refrangible electromagnetic waves with frequencies higher than those that humans identify as the color violet.
UV light is typically found as part of the radiation received by the Earth from the Sun. Most humans are aware of the effects of UV through the painful condition of sunburn. The UV spectrum has many other effects, including both beneficial and damaging changes to human health. Read More …
Ultraviolet (UV) light has shorter wavelengths than visible light. Though these waves are invisible to the human eye, some insects, like bumblebees, can see them! Read More …
Sunlight and Solar Energy
The energy produced by the sun is electromagnetic radiation with many different wavelengths. Only a small portion of these wavelengths are visible to the human eye. These visible wavelengths are seen as colors of the rainbow depending on the wavelength. Red has the longest visible wavelength and violet has the shortest visible wavelength. When all the waves are seen together, they make white light.
Waves longer than those seen as red, are called infrared. Waves shorter than violet are called ultraviolet. Ultraviolet light comes in different lengths too.
Effect of UV Light on Skin
While some sunlight is necessary, too much exposure to the sun’s invisible ultraviolet A and B rays can cause sunburn, premature aging of the skin, skin cancer, and other health effects.
UV Light Can Harm your Eyes
Exposure to ultraviolet (UV) radiation can harm the eyes and affect vision as well.
According to the American Optometric Association (AOA), even on an overcast day, harmful UV rays can cause sunburn of both the skin and the cornea of the eye. Over time, unprotected exposure to the sun can increase the possible risk of certain types of cataracts and potentially damage the retina, which could lead to total blindness.
UV Sensitive Beads
UV-sensitive beads contain a pigment that changes color when exposed to ultra-violet light from the sun or certain other UV sources. The pony beads are not, however, affected by visible light and so will remain white indoors or when shielded from UV light.
The electromagnetic radiation needed to affect change is between 360 and 300 nm in wavelength. This includes the high-energy part of UV Type A (400-320 nm) and the low energy part of UV Type B (320-280 nm). Long fluorescent type black lights work well. Incandescent black lights, the type used to make fluorescent paints glow, will not change the color of the beads, nor will UV Type C (280 –1 nm).
What is UV Index?
The UV Index is the forecasted amount of skin damaging UV radiation expected to reach the earth’s surface at the time when the sun is highest in the sky (solar Noon). The amount of UV radiation reaching the surface is primarily related to the elevation of the sun in the sky, the amount of ozone in the stratosphere, and the amount of clouds present. The UV Index can range from 0 (when it is nighttime) to 15 or 16 (in the tropics at high elevations under clear skies). UV radiation is greatest when the sun is highest in the sky and rapidly decreases as the sun approaches the horizon. The higher the UV Index, the greater the dose rate of skin damaging (and eye damaging) UV radiation. Consequently, the higher the UV Index, the shorter the time before skin damage occurs.
What is SPF?
SPF stands for the Sun Protection Factor provided by a sunscreen. It refers to a product’s ability to stop your skin from burning. The higher the number of the SPF, the longer you can stay in the sun before burning.
For example, if it normally takes 10 minutes of sun exposure for skin to get a sunburn, an SPF of 15 would ideally provide 150 minutes of protection. (In actual use, protection is less because sunscreen gets washed off by sweat and water.) An SPF of 15 blocks more than 92 % of the UVB rays.
|atmosphere||A thick mass of air that surrounds the Earth contain many layers.|
|cataracts||A clouding of the lens of the eye that prevents light from passing through the membrane. Can cause blindness.|
|cloudy||Having many of a visible mass of particles of condensed vapor in the atmosphere.|
|cornea||The transparent part of the membrane that covers the pupil and allows light to enter the eye.|
|dermatologist||A doctor who studies the skin, its structure, its function and its diseases.|
|energy||The capacity for producing power such as heat or light.|
|exposure||To allow to be unprotected and risk harm from that.|
|meteorologist||A scientist who studies the weather ophthalmologist A doctor who deals with the structure, functions, and diseases of the eye.|
|overcast||A thick layer of clouds that obscure some of the sun’s energy.|
|ozone layer||A form of oxygen formed naturally in the atmosphere by a photochemical reaction and located mainly in the stratosphere.|
|solar||Having to do with the sun.|
|solar astronomer||A scientist who studies the sun|
|SPF||Sun Protection Factor that is a number used to describe how much protection from ultraviolet rays a sunscreen will give.|
|stratosphere||A part of the Earth’s atmosphere that extends from about 11 kilometers above the Earth’s surface to about 50 kilometers and contains the ozone layer.|
|sunburn||An irritation of the skin caused by too much exposure to ultraviolet rays.|
|sun||The star nearest to Earth that gives off the energy (heat and light) that affects the Earth|
|UV||Ultraviolet radiation or energy given off by the sun that cannot be seen.|
|UVA||Part of Ultra Violet radiation with wavelength of 320 to 400 nm|
|UVB||Part of Ultra Violet radiation with wavelength of 290 to 320 nm|
|UVC||Part of Ultra Violet radiation with wavelength of 100 to 290 nm|
|UV Index||A special scale developed by the EPA that forecasts the amount of ultraviolet radiation that will reach the Earth’s surface.|
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to identify the presence of UV radiation and Compare the strength of ultraviolet radiation in direct sunlight in different times of the day.
Question: How does the strength of UV radiation from the sun change in different hours of a day?
What times of the day sunlight emits the highest amount of UV radiation?
Other experiment ideas:
- Compare the strength of ultraviolet radiation in the shade in different times of the day.
- Test sunglasses for their ability to filter UV light.
- Test sunblock/ sunscreen lotions for their effectiveness in blocking UV radiations.
Objectives and Benefits for Students
- Students will understand that the sun gives us more than just visible light.
- Students will understand that the sun gives off invisible energy we can’t see such as ultraviolet rays.
- Students will develop an understanding of how to protect their bodies from the harmful effects of sunlight.
- Students will develop an understanding that the Earth’s atmosphere shields the surface of the Earth from most of the ultraviolet rays that come from the sun.
- Students will explore/demonstrate the effects of ultraviolet radiation on objects that react to ultraviolet rays.
- Students will become familiar with the work of an ophthalmologist, dermatologist, meteorologist and solar scientist.
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
This is how you may define variables for the main question of this project (Tested in experiment 1)
- Independent variable is the time of the day
- Dependent variable is the strength of UV light measured as the number of seconds it takes for UV sensitive beads to loose their color after stopping exposure to the UV.
- Constants are the UV beads used for the experiment
- Control variable is the condition of cloud or any natural phenomena that may block the sunlight.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
This is a sample hypothesis:
I hypothesize that UV light from the sun will be maximized at mid day.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Compare the strength of ultraviolet radiation in direct sunlight in different times of the day
The speed of color change in UV sensitive beads and the length of time the color will remain vary based on the strength of the UV radiation. We will benefit this property of light sensitive beads to compare the strength of UV radiations.
- Take all your beads outside under direct sunlight and separate different colors. You will have yellow, pink, red and blue or purple beads. Keep each group in a separate cup or bag. Label them so you will know what color they are because they will soon become colorless or white after you bring them back in. In this experiment you will only use blue/purple beads.
- Place the beads in a small petri-dish or a small plate. Cover them with a dark cloth
- Early morning immediately after sunrise take your blue beads outside in sunny space, remove the cloth and hold them exposed to the sunlight for 3 minutes.
- Cover the beads again with the cloth and immediately start taking the time using a stopwatch or regular watch. Quickly bring back the beads in a low light room and wait until the beads loose their color and become white again. Record the number of seconds it took for the beads to become white again.
- Repeat the steps 2 and 4 once every one hour and record your findings in a table like this:
|Time of the day||Seconds taken to loose color||Notes|
If at any of the hours there are clouds covering the sun, make a note of that in the notes column of your data table. For a valid reliable data you must do your experiment in a day with clear sky or no clouds.
The times you make your observation does not have to be at the top of each hour. For example if the sunrise is at 6:25, your next observations will be at 7:25, 8:25,…
Make a graph:
You can make a bar graph to visually present your results. Make one vertical bar for each of your observation. Write the time of observation bellow the bar it represents. The height of each bar will show the number of seconds it took for the color to disappear.
The image in the right shows a partial graph for this project. In this graph, the sunrise was at 5:00 am, but the first observation was made at 7:00 a.m.
The numbers bellow the bars are observation hours.
Your graph may be different depending on the season, your geographic location and the beads you use for your observations. Almost in all cases your graph will show that the UV radiation from the sun is maximized in the mid day.
Compare sunscreen lotions for their effectiveness in blocking UV radiations.
Sunscreens partially filter the UV radiation. The lower the UV radiation is, the more it takes for the UV sensitive beads to show colors. The time taken to change color can be measured and used as an indication for the action of sunscreen. On the other hand if sunscreen is blocking part of the UV radiation, then beads absorb less energy and they will loose their color in a shorter time after stopping the UV exposure.
Take 3 sets of UV beads and soak one set each in sunscreen SPF 15, SPF 30+, and SPF 45+. Let each dry for about 60 minutes before beginning the exploration. (Note: Drying the beads is optional as the beads will change color when exposed to the sun while they are still wet with lotion.) Label each set with the type of sunscreen used covering it.
Take another set of UV beads and do not apply any sunscreen to that set. Label it control.
Place each set of beads on a sturdy paper plate and cover each with a dark cloth as you position them outside.
Start recording the time and immediately remove all four cloths to expose all four sets to direct sunlight. Measure and record the number of seconds it takes for each set to become colorful.
Cover all plates and immediately start recording the time. Then immediately bring the plates to a low light room and remove the cloths. Measure and record the number of seconds it takes for each group of beads to become white again.
Record your results in a table like this:
|Sunscreen lotion||Time to get color||Time to loose color|
Other Related Experiment 2
- Compare the strength of ultraviolet radiation in the shade in different times of the day.
- Compare the strength of mid day ultraviolet radiation in clear sky and trough the clouds.
- Test sunglasses for their ability to filter UV light.
Materials and Equipment:
List the materials and equipment you use in this section of your report. This is a sample list of materials for all experiments in this page.
- UV sensitive beads (MiniScience Product code: UVB1)
- Timer or watch
- Notebook and pen
- A low light room near your observation space
Sunscreen cream/ lotion
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
If you do any calculations, write your calculations in this section of your project guide.
Summery of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
List your references in this section of your project guide.