Which Sunglass Lens Type Offers the Best Absorption of Ultraviolet Light?

Type

Physical Science

Grade Level

Middle School Level (Grades 6-8)

Difficulty of Project

Easy

Cost

$3.50 for the UV Detector, and cost will vary for the different sunglass types

Safety Issues

1. Investigator should not look directly at the Sun while using the UV detector as it may cause permanent eye damage, nor stay exposed to the Sun's ray for a prolong time period.
2. The UV Detector tube contains beads pieces that are small which may be considered a chocking hazard if placed in the mouth. Children under 3 years old should not handle the detector tube. Material Availability (Are the materials required readily available?) The UV Detector can be purchased from an online supplier. The sunglasses, masking tape, and Tri-fold cardboard display board can be purchased locally.

Approximate Time Required to Complete the Project (hours, days, weeks)

Less then one day once the materials are secured.

Objective

What is the project about?

The research aspect of this science fair project is to determine which sunglass lens type and/or tints and coatings best absorbs ultraviolet (UV) light. 

What are the goals?

To use a UV-Detector to determine the intensity of ultraviolet light that is transmitted through sunglass lens as indicated by the detector. Using the data gathered the information will be displayed in a data table and as a graph. The information gained from this study will be of benefit by presenting scientific data in support of the best sunglass lens type to reduce the chance of eye damage due to ultraviolet light over exposure. 

Materials and Equipment / Ingredients

What materials are required?

UV Light Detector, various sunglass lens types and tints (Blue-blockers lenses, polarized lenses, mirror-coated lenses, gradient lenses, double gradient lenses, and photo-chromic lenses), an empty shoe size box, masking tape, a pair of scissors, and a Tri-fold cardboard display board.

Where can the materials be found?

1. The sunglasses can be purchased or "borrowed" for this science fair project, from any local eye care store, optometrist office, sunglass recycling facility or charity that collects used sunglasses. Some eye care chain stores may be willing to "lend" unused sunglass lens minus the frames.
2. The UV Bead Detector can be purchased online from Science in a Bag or Educational Innovations.

Introduction

Earth's atmosphere prevents most ultraviolet (UV) radiation given off by the Sun from reaching the ground the radiation tends to be screened out by stratospheric ozone which is about 35 km above the Earth's surface. UV radiation has both positive and negative effects. Positive effects of UV radiation include warmth, light, photosynthesis in plants, and vitamin D synthesis in the human body. However, too much exposure to UV causes the skin to burn and leads to wrinkled and patchy skin, cataracts, and even skin cancer.

In this activity the young investigator will use a detector composed of two or three UV-beads inside of a clear tube to measure ultraviolet levels. UV-sensitive beads contain photo-chromatic dyes that react to UV light and cause the normally white beads to change into vibrant colors when exposed to sunlight. When the detector is shielded from UV radiation, the beads are white when exposed to the sun's ultraviolet radiation the beads turn purple even on a cloudy day. As the intensity of UV radiation increases the darker the color, and conversely the less UV intensity the lighter the color. The detector contains a color scale which enables the user to determine the UV index.

The job of the sunglass is either to absorb or reflect UV ultraviolet light in order to protect the eyes. This occurs at various stages as the light hits the outside of the lens, the interior of the lens, and the back of the lens. Sunglass lenses are characterized by the specific eye protection that they offer. The following is a list of the various sunglass lens categories:

Blue-blockers-block blue light and usually has amber lenses. These lenses are used mostly by skiers, hunters, boaters and pilots who use them to heighten contrast.

Both polarized lenses and anti-reflective coating lenses cut reflected glare. Polarized lens are generally worn by those who play water and snow sports. The anti-reflective coating reduce glare caused by light reflecting off the back surface of the sunglass lens.

Mirror-coated lenses limit the amount of light entering the eyes. Because they are highly reflective coatings applied to the front surface of the lenses to reduce the amount of light entering the eye.

Gradient lenses are tinted from the top down, so that the top of the lens is darkest. Double gradient refers to lenses that are also tinted from the bottom up, the top and bottom are darkest and the middle has a lighter tint.

Photo-chromic lenses adjust their level of darkness based on the amount of UV light they're exposed to.

Sunglass tints do not affect the amount of ultraviolet light that reaches the eyes, and dark sunglass lenses are no more effective at protecting the eyes then light ones; UV protection is completely independent of both color and sunglass lens thickness.

Diagrams and Pictures

Digital photos can be taken during the experimenting process and an image of the UV Detector can be downloaded from the Science in a Bag website for free and without copyright infringement issues.

The following websites also offer down loadable images of sunglasses that can be used on the Tri-fold cardboard display board: