Which Type of Sunglass Lenses Gives the Best Sun Protection?
Determine which sunglass lens type and/or tints and coatings gives the best sun protection by absorbing ultraviolet (UV) light. Use a UV-Detector to determine the intensity of ultraviolet light that is transmitted through sunglass lens as indicated by the detector. Figure out the best sunglass lens type to reduce the chance of eye damage due to ultraviolet light overexposure.
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 damages skin cells and leads to wrinkled and patchy skin, cataracts, and even skin cancer.
In this activity, you 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 turn purple, even on a cloudy day. As the intensity of UV radiation increases. the color gets darker. The detector contains a color scale which enables the user to determine the UV index.
The job of sunglasses 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:
Blue-blockers block blue light and usually have 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 minimize reflected glare. Polarized lens are generally worn by those who play water and snow sports. The anti-reflective coating reduces glare caused by light reflecting off the back surface of the sunglass lens.
Mirror-coated lenses limit the amount of light entering the eyes. 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, so that the top and bottom are darkest and the middle has a lighter tint.
Photo-chromic lenses adjust the level of darkness based on the amount of UV light they're exposed to.
Sunglasses 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 lens thickness.
- 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.
- 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.