The Effect of Light Intensity on Visual Acuity in Sixth Graders
Researched by Charlie Ann G. 2002-03	PURPOSE  HYPOTHESIS  EXPERIMENT DESIGN  MATERIALS  PROCEDURES  RESULTS  CONCLUSION  RESEARCH REPORT  BIBLIOGRAPHY  ACKNOWLEDGEMENTS  ABOUT THE AUTHOR

The purpose of this experiment was to determine the effect of light intensity on visual acuity. 

I became interested in this idea when I went to an eye appointment and had been lying back looking into the light for a while.  I noticed that the room looked different when the light was turned down lower.

The information gained from this experiment would benefit schools and businesses, because they would know the intensity of light needed for easy reading and good worker productivity.

HYPOTHESIS

My hypothesis was that the best amount of light to see in would be a medium-bright light, about 245 lux, because I find it easiest to see when a light isn’t too dim, but it’s not so bright that I can’t work very well.

I based my hypothesis on Dale Graf, optometrist, who said that if light is below the optimum level, the retina doesn’t receive enough light to produce a good visual image, but if it is above the optimum level, there is a glare, so again, there’s not a good image on the retina.

The constants in this study were:
 

• The acuity posters used to tell how well subjects can see
• The distance the subjects are from the poster.
• The approximate age of the subjects.
• The place where the experiment took place.
• The instrument I used to measure the amount of light in the room.
• The light source in the room

The manipulated variable was the amount of light reflecting from the acuity wall chart.

The responding variable was the subjects’ visual acuity. 

To measure the responding variable each subject read the letters on a visual acuity wall chart.  The number of letters read correctly was recorded as the Visual Acuity.

MATERIALS

QUANTITY	ITEM DESCRIPTION
20	Human Subjects
1	Rheostat
1	Light meter
5	Wall charts
1	Computer program "Logger Pro"

PROCEDURES

1. In a windowless room, set up your experiment:
a. Tape up a wall chart on one of the walls.

b. Put a chair 6.1 meters away from the wall chart. 
c. Set up a rheostat so you can dim the lights.
d. Set up a light intensity meter so you can measure the amount of light in the room.
e. Using a light intensity meter, measure the amount of light .reflected off of the wall chart in each light level, and record it.
2. Obtain 20 volunteers.
3. Bring two volunteers to room and explain experiment.
4. Get into the computer program "Logger Pro".
5. Adjust the light so it is at 780 Lux.

6. Have one sit in the chair and read the letters on the wall chart as best as they can.
7. Record the results.
8. Repeat steps three to five with 260 Lux, 90 Lux, 30 Lux, and 10 Lux .
9. After subject is done, have them return to class.
10. Repeat steps 3-8 for all remaining subjects.
11. When every subject is done being tested, score all of their results in each light level, depending  on how many they got right, out of how many letters they read total.
12. Determine which light level was easiest to see in depending on your subjects’ tests.

RESULTS

The original purpose of this experiment was to determine the effect of light intensity on visual acuity.

The result of this experiment was that 759 lux, or bright light, is the easiest to see in.

See my table and graph.

CONCLUSION

My hypothesis was that the best amount of light to see in would be a medium-bright light, about 245 lux, because I find it easiest to see when a light isn’t too dim, but it’s not so bright that I can’t work very well.

The results indicate that this hypothesis should be rejected, because the easiest light to see in was brighter than I thought it would be.

Because of the results of this experiment, I wonder if there is an even brighter light that would be easier to see in, and I also wonder if there is a difference in male’s and female’s eyesight in different vision.

If I were to conduct this project again I would probably have had the highest light level brighter than it was.  If I did this, there might be a light that is even easier to see in than the one I used, 759 Lux.
 

Research Report The human eye is the organ of sight.  It has many parts that help us with the process of vision. The Eye Outer Parts The human eye is made up of three layers of tissue, the sclera, choroids, and the cornea.  The outside layer, the sclera, is the white part of the eye.  It acts as a protective shield of the eyeball.  The sclera covers 5/6 of the surface of the eye.  It is made up of tough tissues which give the eyeball strength.  The middle layer is the choroid.  The choroid is a vascular layer lining 3/5 of the eyeball. The layer on the front of the eyeball is the cornea.  It is a tough, five-layered membrane where light is admitted into the middle of the eye.  The cornea, like the sclera, is made up of tough tissues that give the eyeball strength.  Without any blood vessels, and because the cornea is somewhat dehydrated, it is transparent  The cornea lies in front of the iris, or the colored part of the eye. The conjunctivita, which is not a layer of tissue, is a membrane that lines the inside of the eyelids and extends over the front of the sclera.  The conjunctivita makes slimy, transparent fluid that moistens the eyeball.  It produces some tears, which help keep the eye clean. Most of the tears that come out of the eye are produced by the lacrimal glands, which lie at the upper, outer corner of each eye. The lacrimal sac is a pouch at the lower, inner corner of each eye.  "Every time a person blinks, the eyelids spread a smooth layer of mucus and tears over the eye.  These fluids then flow into tiny canals in the lids."  This is why after crying, someone may have to blow their nose, to clear it of excess tears.  Quote from World Book Encyclopedia, Eifrig, David E.  "The Eye" The eyelids protect the front of the eyeball, and the eyelashes shield off tiny particles in the air, such as dust.  Any quick movement in front of the eye, or anything touching the eyelids causes the eyelids to blink in a protective reflex action. Inner Parts The iris is the colored part of the eye and it lies behind the cornea.  The color of the iris comes from a substance called melanin.  If there is a lot of melanin, and it is near the surface, the color of the iris will be darker.  Melanin also soaks up very strong light that would otherwise blur vision.  Melanin is the same substance that gives hair and skin their color. The black circle in the middle of the iris is the pupil, which controls the amount of light let into the eye.  Two muscles in the iris adjust the size of the pupil to the level of light.  In dark or dim light, the dialator muscle makes the pupils bigger, so they can allow as much light as possible into the eye.  In bright light, the sphincter muscle makes the pupils smaller, which prevents too much light coming in.  The ocular muscles are six muscles that are connected to the eyeball.  They give the eyeball the ability to move all around.  Inside the eye in front of the iris, is a watery fluid called aqueous humor.  Vitreous humor fills almost all of the rest of the eye.  The humors help the eye hold its shape, and without them, the eyeball would collapse. Immediatley behind the pupil lies a clear round window of tissue—the lens.  The lens is attatched to a surrounding network of muscles, or the ciliary muscles.   The ciliary muscle contracts and flattens the lens or makes it bulge out so it can focus on the retina.  The lens’ ability to flatten or bulge out is called accommodation.  Accommodation is the reason people can clearly see  both far away and close up.  However, some people are near or farsighted, which means that their ciliary muscle doesn’t flatten or bulge the lens the right amount.  This is where eyeglasses and contact lenses come in.  They alter the angle where light rays enter the eye so light can hit the retina correctly and form a clear visual picture. The ciliary body circles the iris.  It is connected by fibers to the crystalline lens, which is right behind the iris.  The crystalline lens is flexible, and like the cornea, it has no blood vessels and is somewhat dehydrated, therefore it’s transparent.  The muscles in the ciliary body constantly adjust into the shape of the lens.  These changes make a good visual picture at all times. The Retina The retina forms the inside layer of the wall of the eyeball, and it is very fragile.  Cells in the retina absorb light rays and change them into electrical signs.  There are two types of these cells--cones and rods. The retina has 120 million rods and 6 million cones.  Little bits of pigment in the rods and cones can absorb tiny particles of light that hit the retina.  This pigment is called visual purple or rhodopsin.  Rhodopsin allows the eye to see different shades of gray and in dim light.  There are three different types of pigment in cones.  Cyanolabe absorbs all blue lights,  Erythrolabe absorbs all red lights, and Chlorolabe absorbs all green lights.  All of these pigments allow us to distinguish more that 200 colors. Macula lutea is a round area made up of mostly cones, near the center of the retina.  It creates a sharp image of objects where the eyes are directly aimed. The rest of the retina allows the eye to see objects that are off to the side, while the eye is looking forward.  Most of the rods are in this part of the retina.  Rods are more sensitive in dark than in light, and because of this, it is easier to see faint objects if the eyes aren’t aimed directly at them. Nerve fibers that are connected to cones and rods join in the middle of the retina and form the optic nerve, which is made up of about a million cells.  "It serves as a flexible cable that connects the eyeball to the brain."  The retina and the optic nerve are extensions of the brain.  The optic nerve transports electrical signals made in the retina to the brain, and the brain "interprets them as visual images."  Quote from World Book Encyclopedia, Eifrig David E. "The Eye" Where the optic nerve enters the eye is known as a person’s blind spot.  This spot has no rods or cones, so it can’t respond to light.  A person normally doesn’t notice their blind spot, because it’s so small, and the eye’s movements are so quick.  Anything in the blind spot of one eye, the other eye can see. Light Light is electromagnetic radiation visible to the human eye.  It is a form of energy that "travels through empty space" at about 186,000 miles per second.  In the early 19th century, light was "described in terms of waves", although later experiments showed that light showed properties of particles.  Light is the source for sight and perception of color.  The eye can tell the color of an object when that same colored light reflects off of the object. Quote from web address: http://www.education.yahoo.com Reflection Reflection is the "return of a wave of energy" such as heat, sound, light, or radiation after it hits a surface.  Echo is a good example of reflection of  sound waves.  Reflection can be like a ball coming off of a wall after it is thrown.  The angle that is made by the path of the ball that is thrown is called the angle of incidence.  The angle that is made by the path of the ball as it is being rebounded is called the angle of reflection.  The principle of reflection is used many times in daily life.  Polished surfaces reflect most of the light that hits them, mirrors also reflect most of the light that hits them, although clear surfaces, such as windows, reflect only a small amount of light.  Quotes from World Book Encyclopedia, "Reflection" Waves Waves are motions that carry energy, for example radio and television have waves that travel to cars and/or homes.  The substances that waves travel through is called the medium.  Waves are caused when the medium is disturbed by an object.  The object that disturbed the medium is called the source of the wave.  Waves may take the shape of hills and valleys, although scientists call them crests (hills), and troughs (valleys).  Wave length is the distance from one point on the wave to another.    Amplitude how much higher the crest, or hill, is than when there are no waves going on.  Frequency is the number of waves made per second. Transverse waves are what cause parts of the medium to move up and down, opposite of the direction the wave is moving, which is back and forth. Longitudinal waves are particles of medium that move back and forth, which is the same direction that the waves are moving. Optics Optics is a science having to do with  the production and motion of light,  the changes it goes through, and related phenomena.  Physical optics are the nature and property of light.  Geometric optics involves devices that use light, such as lenses, mirrors, etc.  The study of optics has let us make lenses, such as glasses, contact lenses, cameras, binoculars, telescopes, microscopes, lasers and optical fibers. Conclusion Both light and the eye work together to form a good visual image at all times, the light reflecting off objects that we see, and the eye forming a good picture on the retina.

BIBLIOGRAPHY Eifrig, David E.  "Eye".  The World Book Encyclopedia.  1998 "Eye."  Microsoft Encarta Encyclopedia Deluxe 2001  CD-ROM Kittredge, Mary.  The Senses.  New York Philadelphia: Chelsea House Publishers,  1990.  Pg 33-35 "Light". Encyclopedia Britannica Online January 23, 2003 <http://www.britannica.com/eb/alpha?search=light&x=11&y=16> Muscari, Joseph A.  "Reflection".  The World Book Encyclopedia. 1998, pg 194  "Optics". Encyclopedia Britannica Online January 23, 2003 <http://www.britannica.com/eb/alpha?search=light&x=11&y=16> "The Human Eye’s Response to Light" Visiual Acuity of the Human Eye.  December  4, 2002  http:://www.cnde.iastate.edu/ncce/PT_CC/Sec. 1 2 3/ Sec. 1.2.3 Treays, Rebecca.  Understanding your Brain.  Oklahoma: EDC publication 1999. Pg. 4-5, 7, 11-12.

ACKNOWLEDGEMENTS

I’d like to thank the following people: 

• Mrs. Helms for helping me set up my experiment each day that I went to conduct it.
• Mr. Newkirk for helping me understand different things about my project and for helping me with my experiment, and editing my journal and report.
• My uncle, Dr. Dale Graf, optometrist, who helped me understand what I was going to do for my experiment
• My mom, for helping me choose my topic, and find information about it.

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