Why do mountaineers have to wear sunglasses when climbing the plateau snow-capped mountains?

Mountaineers always wear a pair of sunglasses when climbing mountains. Why? Actually, it's to protect your eyes.

The air on the mountain is very thin. At an altitude of 8000 meters, the density of air A is only about one-third of the sea level, so the radiation of sunlight is particularly strong. In addition, snow has accumulated on high mountains, hillsides and peaks, and white has a particularly strong reflective ability. On the bare snow slopes or snow peaks, the snow reflects the strong sunlight rudely.

Sunlight contains various colors of visible light, and a lot of ultraviolet and infrared rays radiate from the sun to the earth. The eyes are the most sensitive photosensitive organs of the human body. Intense ultraviolet and infrared radiation on the retina of the eye will burn the retina, resulting in decreased vision and even blindness in severe cases. This phenomenon is called snow blindness in medicine.

Therefore, mountain climbers must wear a pair of special sunglasses to protect their eyes. The lens of this kind of sunglasses is not ordinary glass, but iron oxide and cobalt oxide which can absorb infrared and ultraviolet rays are added to the glass. When these two chemicals are mixed together and added to glass, the glass will turn black. Sunglasses worn by mountaineers are made of this special glass.