The purpose of this experiment was to determine what spectacle lens
material and/or tints and coatings best absorbs ultraviolet (UV) light.
I became interested in this idea because I have an interest in optical
studies. My uncle is an eye doctor and I think his job is fascinating.
I know ultraviolet light can damage the human body, especially the eye.
The information gained from this experiment will benefit society by
reducing the chance of ocular damage due to ultraviolet light over exposure.
My hypothesis is that the polarized lens will best absorb ultraviolet
light of all lens materials with and without tints and coatings tested.
I base my hypothesis on the fact that polarized lenses filter plane-polarized
light, which is reflected light, as well as natural scattered UV light.
The constants in this study were:
The manipulated variable was the type of lens materials, tints, and coatings.
The responding variable was the intensity of ultraviolet light the lens transmits.
To measure the responding variable I used a meter to determine the intensity
of ultraviolet light that was transmitted through the lens and a photometer.
Reflecting box is a cardboard box 32 inches long, 10.5 inches wide and
7 inches deep. There is a 1.5-inch hole (made with cardboard tube) in the
center of the long side of the box. The lower 1/3 of the hole is covered
by duct tape, thus allowing light to be emitted through the upper 2/3s
of the hole. A lens holder was constructed on the interior surface of the
box that allows the lenses to fit centrally and snuggly over the hole.
The exterior side of the opening is constructed with 3 thumbtacks to hold
the lens meter tightly over the opening. All interior surfaces are covered
by aluminum foil accept for the opening. A 19-inch UV lamp arc is placed
behind the opening to allow the middle of the tube to be centered over
the hole. See Table #1 on lens analysis.
Notes: First test should be done with no lens in place to get baseline
findings. Im testing each lens three different ways to get a more accurate
The results of this experiment indicate that the polarized lens best absorbs UV light when compared to other lens materials with different tints and coatings tested ( See table #3 and graph #5). This may be biased by the fact that all the tested polarized lenses were #3 grade sunglasses. When the polarized lenses were compared to other #3 sunglass lenses, all lenses rated above 96% UV absorption, with the plastic lenses absorbing 99.2% and polarized lenses absorbing 99.0% (See table #4 and graph #6).
When comparing crown glass, CR-39 plastic, and polycarbonate (the three most common materials for prescription lenses), there was a profound difference between the sunglass #3 tinted materials and the lighter tints and coatings. The #3 tints absorbed an average of 97% UV light and the lighter tints and coatings absorbed only 59%. Consequently, the protection from UV light is more dependent on the darkness of the tint rather than the lens material (See table #4 and graph #6).
There was no standard protection from the UV light from antireflective coatings (AR) (See table #1 and #2, lenses #4, 9, and 12).
When evaluating the UV protection based on cost, there was no definite difference between high quality lenses and those of low quality (See tables #1 and 2). One definite fact is that all high quality sunglass lenses, regardless of the material, absorb 100% UV light that was tested.
Plastic photochromatic lenses absorbed 100% UV light while glass only absorbed 89% in its darken state (See tables #1 and 2).
In comparing the accumulation of the data, using the reflecting box
and lens meter to the photometer, a significant difference was apparent
in the quality of the data collected.
There was a general trend that with all lenses tested, the less the
visible light was transmitted; the greater the UV was absorbed (See graphs
#3 and 4).
My hypothesis that the polarized lens would best absorb the UV light was proven to be true through the experiment. The polarized lens best absorbs UV light because it was 7.5 percent greater in absorption to the plastic lens, which was the second most efficient lens.
The results of the experiment showed that all materials in a grade #3 sunglass lens absorbed at least 96% of UV-B light.
If I were to conduct this experiment again I would use a photometer because it gave much more precise findings then the lens meter and reflecting box. The results of the lens meter test #1 and #2 did not provide accurate enough results to prove or disprove the hypothesis.
I would also use equal numbers of each lens material and equal numbers of differing levels of tints and coatings. The experiment showed that the darker the lens the better the protection. Therefore, more data collection and analysis is necessary.
Further experiments to enhance the knowledge of UV-B protective eyewear could be:
1) Test lens materials of differing ages to see if aging of the material
significantly affects the UV-B protection.
This experiment has been very thought provoking and I believe can add
important information for the safety of peoples eyes and vision. Definitely,
more studies need to be made regarding this dangerous health risk.
Aqueous humor The clear, watery fluid which fills the anterior chamber of the eye.
Basal cell carcinoma A malignant tumor of epithelial (skin) tissue.
Biological activity A reaction within living tissue.
Choroid The middle coat of the eye lying between the retina and sclera.
Ciliary body The part of the uvea anterior to the ora serrata between the sclera outside and the vitreous and the posterior chamber inside.
Coating A thin deposit of a metallic salt, such as magnesium fluoride, about one fourth as thick as a wavelength of light, applied to the surfaces of a lens.
Cornea The transparent anterior portion of the fibrous coat of the eye.
Cortical cataracts A cataract in which the opacity lies in the cortex of the crystalline lens.
Macular degeneration Degeneration of the macular area of the retina in the aged population which progresses to pigmented scar formation.
Nanometer A unit of length equal to one millionth of a millimeter.
Optic nerve Anatomically, cranial nerve II of the peripheral nervous system.
Photic maculopathy Macular disease caused by extended exposure to extremely bright light.
Photochromatic Pertaining to substances which change in color and in light transmission properties upon exposure to a change of light intensity or to ultraviolet radiation.
Photokeratitis A superficial punctate inflammation of the cornea caused by exposure to ultraviolet radiation or and intense electric spark.
Pinguecula A small, slightly raised, yellowish, nonfatty thickening of the bulbar conjunctiva on either side of the cornea.
Plane-polarized light Polarized light in which the transverse wave vibrations are parallel to a plane through the axis of the beam.
Polarizer An agent or medium which induces or effects polarization.
Pterygium A horizontal, triangular growth of the bulbar conjunctiva, occupying the intrapalpebral fissure, with the apex extending toward the cornea.
Pupil The aperture in the iris, normally circular and contractile, through which the image-forming light enters the eye.
Sclera The white, opaque, fibrous, outer tunic of the eyeball, covering it entirely excepting the segment covered anteriorly by the cornea.
Solar maculopathy Degeneration of the macula from overexposure to the ultraviolet rays from the sun.
Spectrum The spatial arrangement or series of the dispersed components of radiant energy, in order of their wavelengths, emitted, absorbed, or reflected by a substance.
Ultraviolet light Radiant energy of wavelengths shorter than the violet end of the visible spectrum and longer than the roentgen radiations (X-rays), usually considered to be wavelengths from 400 to 20 nm.
Uveal tract The pigmented vascular coat of the eyeball, consisting of the choroids, the ciliary body, and the iris, which are continuous with each other.
Wavelength The distance in the line of advance of a wave from any one
point to the next point at which, at the same instant, the phase is the
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