THE STUDY OF WHICH SHADE OF SUNGLASSES BLOCK THE MOST LIGHT

Transcription

1 THE STUDY OF WHICH SHADE OF SUNGLASSES BLOCK THE MOST LIGHT Kiera Tai Cary Academy ABSTRACT The purpose of this experiment was to determine which color tint of sunglasses would block the most light. Sunglasses have seven layers. From the layer closest to the eye it is the antireflective back, the tinting layer, the lens, the polarization layer, the antireflective coating, the UV coating, and the scratch resistant coating. A flashlight was placed a fixed distance in front of a lens of sunglasses and a light probe was placed a fixed distance behind the lens. The flashlight was turned on and the amount of light that passed through the lens was measured with the light probe. The black tinted sunglasses were found to block the most light. This is probably because it is the darkest color. INTRODUCTION The lenses of sunglasses have seven layers. The layer closest to the eye is the antireflective back, which protects the eye from glare of light from behind. The layer after that is the tinting layer. It is the layer that gives the lens its color. Gray is best for viewing true colors, yellow is good for outdoor activities in low light, and green and brown are soothing in both low and bright light. The next layer is the lens, Figure 1. The 7 layers of sunglasses

2 which is usually made of glass, plastic, or polycarbonate. Glass blocks the least light but is most scratch resistant. Plastic blocks more light but is the cheapest and least durable. Polycarbonate is the lightest, most durable, and blocks the most light. After the lens is the polarization layer, which is many wafer sheets that block horizontal light rays. Next is a UV coating, which filters out ultraviolet rays A and B. Then, there is the antireflective coating which consists of many layers of various metal oxides that reduce glare and sometimes repel water. Lastly, the layer that is farthest away from the eye is the scratch-resistant coating. It is usually made of durable plastic that prevents scratches on the surface of the lens. The eye is the organ that is responsible for sight. The colored area is called the iris and the black spot in the middle of the iris is called the pupil. Light enters the eye through the pupil, and the iris controls how much light enters. The iris is made up of muscle fibers that lengthen and shorten to make the pupils larger or smaller. When it is bright, the pupils become smaller, letting less light in since there is already a lot of light. When it is dark, the pupils become larger, to allow more light to enter so it can see more. The pupil is covered by the cornea, which is like a clear window Figure 2. The human eye that is not visible. Behind the pupils are the lenses. The lenses are like small curved pieces of jelly that are held in place by small muscles. When light enters through the pupil, it passes through the lens. The lens bends the light so it focuses on the retina, which is the back of the eye where images are formed. Images form upside down on the retina. Receptor cells send messages to the brain along a large nerve. The brain receives this information and makes sense of it. It turns the image right side up, mixes colors, and figures out how far away and big things are. When the light doesn t focus on the retina, a blurred picture will be formed. The retina has millions of tiny receptor cells. There are two types of receptor cells: cones and rods. Cones react to colors making it possible to see in bright light, while rods react to black and white and allow seeing in dim light. Each eye has about 6 million cones and 120

3 million rods. The retina has a blind spot, where there are no rods of cones, so nothing can be seen at that spot. When both eyes are open, there isn t a blind spot because the images that each eye sees overlap each other and cover up each blind spot. The eyelids protect the eyes when sleeping and act as windshield wipers, tears wash eyes in case anything got in them, and the eyelashes keep out dust. Light is waves of electromagnetic energy. It travels at 186, 282 miles per second. The size of a wave is measured by its wavelength. The amount of energy in a light wave is proportionally related to its wavelength. Shorter wavelengths have higher amounts of energy, and longer wavelengths have a lower amount of energy. Light is responsible for the sense of sight. Of visible light, violet has the most energy and red has the least energy. Above the visible light spectrum on the violet side is ultraviolet light, also known as UV light. Sunlight is full of UV light, which can damage the cornea and the retina. Refraction is the change of direction in a light wave due to a change in speed. An example of refraction would be when a stick is placed in a bowl of water. The light rays bend when traveling from the air to the water. The Figure 3. The effects refraction has on how the human eye sees things eye perceives the bent line as a straight line, making the stick seem like it is floating a bit above the bottom of the bowl. Reflection is the throwing or bouncing back of light from a surface. The incoming ray hits the surface, and then it bounces back as an outgoing ray. The outgoing ray will always make the same angle as the incoming ray. Absorption is when a substance obtains light when light passes through it. For example, cement walls absorbs sunlight. The amount of light absorbed is equal to the amount of light reradiated. An experiment done by a student at Cary Academy last year tested which brand of sunglasses blocked the most light. It was found the Mom s brand of sunglasses blocked the most light, Livestrong sunglasses blocked the second most light, Claire s

4 sunglasses were blocked the third most light, and the Target brand sunglasses blocked the least light. MATERIALS AND METHODS In this experiment a flashlight, sunglasses with grey tint, sunglasses with black tint, sunglasses with orange tint, a light probe, a dropper, water, and salt were used in this experiment. For the first experiment, a flashlight was first placed 4cm front a light probe. The flashlight was turned on and the amount of light that it gave off was measured. This was repeated three times and an average was determined. Next, the flashlight placed 2cm in front of a lens on a pair of grey tinted sunglasses and a light probe was placed 2cm behind the sunglasses. The flashlight was turned on and the amount of light that passed through the sunglasses was collected with the light probe. The data was collected three times and an average was determined. This was repeated for the sunglasses with black tint and the sunglasses with orange tint. For the second experiment, a flashlight was first placed 2cm away from a light probe. The amount of light that it gave off was measured three times and an average was determined. This process was repeated when the flashlight was 6cm, 10cm, and 20cm away from the light probe. Then, the flashlight was placed 1cm in front of a lens on the sunglasses with grey tint and a light probe was placed 1cm behind the sunglasses. The flashlight was turned on and the amount of light that passed through was collected three times and the average was determined. Then the flashlight was placed 3cm in front of the lens and the light probe was moved 3cm behind the lens. The flashlight was turned on and the amount of light passing through the sunglasses was measured three times and the average was determined. The flashlight was then moved so that it was 5cm in front of the lens and the light probe was moved so that it was 5cm behind the lens. The flashlight was turned on and the amount of light that passed through the sunglasses was measured three times and the average was determined. Then the flashlight was placed 10cm in front of the lens and the light probe was placed 10cm behind the lens.

5 The flashlight was turned on and the amount of light that passed through the sunglasses was measured three times and the average was determined. This process was repeated for the sunglasses with black tint and orange tint. For the third experiment, a flashlight was placed 5cm in front of one of the lenses on the black sunglasses and a light probe was placed 5cm behind the lens. The flashlight was turned on and the amount of light that passed through the sunglasses was measured with the light probe. This was repeated three times and an average was determined. Then, 10 drops of water were put onto one of the lenses of the sunglasses with a dropper. Then, the flashlight was placed 5cm in front of the sunglasses and the light probe was placed 5cm behind the sunglasses. The flashlight was turned on and the amount of light that passed through was measured. This process was repeated three times and an average was determined. Then 10 drops of salt water was placed on the lens. The salt and the water had been mixed to be proportional to real sea water, (35 g/l). The flashlight was placed 5cm in front of the lens with salt water on it and the light probe was place so that it was 5cm behind the lens. The flashlight was turned on and the amount of light that passed through was measured. This was repeated three times and an average was determined. RESULTS AND DISCUSSION In the first experiment, the black tinted sunglasses were found to block the most light, orange tinted sunglasses blocked the second most light, grey tinted sunglasses blocked the least light out of the sunglasses, and there was the most light with no sunglasses. (see Figure 1). With no sunglasses, there was an average of lux. With the black sunglasses, there was an average of lux. With the orange sunglasses there was an average of lux. With the grey sunglasses there was an average of lux. The black sunglasses probably blocked the most light since black is the darkest color out of the three.

6 Amount of LIght (lux) No Sunglasess Gray Tinted Black Tinted Orange Tinted Type of Sunglasses Figure 4. The effect different colored tint has on the amount of light sunglasses can block In the second experiment, the amount of light decreased for all of the sunglasses and for no sunglasses as the distance between the flashlight and the light probe increased. (see Figure 2). There were different patterns in the way the numbers decreased. When there were no sunglasses, the amount of light dropped quickly from 1cm to 5cm and went into a more graduate drop from 5cm to 10cm. The grey and orange tinted sunglasses had a constant decreasing rate. This is probably because the grey and orange tint did not block most of the light at first, so what was making the amount of light decrease was the decreasing distance. The black tinted sunglasses dropped rapidly from 1cm to 3cm and stayed at almost 0 from 3cm to 10cm. This is probably because, unlike the grey and orange tinted sunglasses, it had already blocked most of the light at 1cm and when it was moved farther away, it already had most of the light blocked and now it was also farther away, so there would be virtually no light. When there were no sunglasses and the flashlight was 2cm from the light probe, there was an average of lux. When there were no sunglasses and the sunglasses was 6cm from the light probe there was an average of lux. When there were no sunglasses and the flashlight was 10cm from the light probe there was an average of lux. When there were no sunglasses and the flashlight was 20cm from the light probe there

7 Amount of Light (lux) was an average of 45.6 lux. With the grey tinted sunglasses, there was an average of lux when the flashlight and the light probe were each 1cm away from the lens. When the flashlight and light probe were each 3cm away from the lens on the grey tinted sunglasses there was an average of lux. When the flashlight and the light probe were each 5cm away from the lens there was an average of 138 lux. And when the flashlight and the light probe were each 10cm from the lens there was an average of 45.2 lux. With the orange tinted sunglasses there was an average of lux when the sunglasses and the light probe were each 1cm away from the lens. When the flashlight and the light probe were each 3cm from the lens there was an average of 72.3 lux. When the flashlight and the light probe were each 5cm away from the lens there was an average of 37.7 lux. When the flashlight and the light probe were each 10cm from the lens there was an average of 10.4 lux. For the black tinted sunglasses, there was an average of lux when the flashlight and the light probe were each 1cm from the lens. When the flashlight and the probe were each 3cm from the lens the average dropped to 43.2 lux. When the flashlight and the light probe were each 5cm away from the lens there was an average of 8.8 lux. When the flashlight and the light probe were each 10cm from the lens there was an average of 10.9 lux No Sunglasses Gray Tinted Black Tinted Orange Tinted Distance Away from Sunglasses (cm) Figure 5. The effects distance has on the amount of light sunglasses can block

8 Amount of Light (lux) In the third experiment, salt water on the lens was found to block the most light, followed by water on the lens, and then nothing at all on the lens. (see Figure 6). The amont of light that passed through the lens with salt water averaged 42 lux. When there was water on the lens, there was an average of 46.1 lux. When there was nothing on the lens, there was an average of 62.6 lux None Water Salt Water Liquid on Sunglasses Figure 6. The effect different liquids have on the amount of light sunglasses can block CONCLUSION Black tinted sunglasses were found to block the most light. It was expected that the black tinted sunglasses would block the most light, but it was not expected that the orange sunglasses would block more light than the grey sunglasses. The greater the sunglasses are from the light source the less light there is. This was expected. Salt water on the lens will block more light than regular water and if there was nothing on the lens. This was also expected. These results are important to others because when buying sunglasses, one might have to consider what color tint to buy. And interesting experiment to do in the future would be to test which brand or tint of sunglasses will block the most UV light compared to regular light.

9 CITATIONS Cowen, Meghan. The Study of Seeing Which Sunglasses are Best to Use. Cary Academy. Jan 12, Print. Dineen, Jacqueline. The Five Senses. Englewood Cliffs: Burdett Press, Print. How A Good Pair Of Shades Protect Your Eyeballs. Esquire. Hearst Communications, Inc. Web. Jan 19, "Radiation." Compton's by Britannica. Encyclopædia Britannica Online School Edition. Encyclopædia Britannica, Inc., Web. Jan 27, Tischler, Steve. How to Choose Sunglasses. REI. Web. Jan 19, Tyson, Jeff. How Sunglasses Work. Howstuffworks. HowStuffWorks, Inc. Web. Jan 20, Wikipedia Contributors. "Reflection (physics)." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 1 Feb Web. Jan 27, Wikipedia Contributors. "Refraction." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 8 Feb Web. Jan 27, Wikipedia Contributors. "Seawater." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 15 Feb Web. Feb 2, Wikipedia Contributors. "Light." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 8 Feb Web. Jan 27, Zamora, Antonio. Anatomy and Structure of Human Sense Organs. Scientific Psychic. Scientific Psychic. Web. Feb 10, 2012.

10 Zeman, Anne and Kelly, Kate. Everything You Need to Know About Science Homework. New York: Scholastic Inc, Print.