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Earth Sense: Sunlight is filtered into different colors to the eye
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After a clammy early spring, the sun is back finally. It’s going to rise toward its highest point in the sky by June 21, the longest day of the year. Measured as an angle from the ground, in Gainesville the sun will be about 78 degrees up. It can’t ever be exactly vertical above us because the subsolar point, where the sun is perpendicular above the ground, doesn’t move this far north.

Still, North Georgia gets the same intensity of sunlight as northern Africa. Because light breaks down into various wavelengths, some are more trouble than others. Human eyes can see wavelengths as short as 400 nanometers (nm). This means there are about 2.7 million of these visible waves per linear yard. The “shortest” color we perceive is violet.

Our eyes are more sensitive to the next longer wavelength, which is blue. Because these short waves get scattered around easily, the sky appears blue when it’s clear. But this is where our eyes have a quirk. Blue doesn’t focus as well as green or red, which have longer wavelengths. Therefore, on a hazy blue day, distant objects appear slightly blurred.

For drivers or sport shooters, sunglasses with orange or brown tinted lenses can produce sharper vision. The orange color filters out some of the blue, eliminating the scatter, and the eyes can focus on the wavelengths that they pick up better. In light daytime fog, I’ve had good results with orange sunglasses to cut through the haze.

Wavelengths shorter than the human eye can perceive are “beyond violet,” or ultraviolet. It’s a type of sunlight that the human skin needs in moderation to produce vitamin D. That, in turn, is essential for healthy bones. Patients with bone density loss, which makes the bones more vulnerable to breaking, are often advised by physicians to get more sunlight exposure and take vitamin D supplements.

Too much of a good thing is harmful, and so is ultraviolet light. Overexposure to sunlight causes sunburn, and in extreme cases, skin cancer. Basal cell carcinoma looks like red patches or open sores on the skin. Fortunately, it doesn’t tend to spread to other parts of the body, and is rarely life-threatening.

But the other type of skin cancer, malignant melanoma, is a killer with 10,000 U.S. victims annually. Good prevention measures include using a high-quality sunscreen, and following doctor’s recommendations when more sun exposure is needed.

 Rudi Kiefer, Ph.D., is a Professor of Physical Science and Director of Sustainability at Brenau University.

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