When exactly should I be wearing sunglasses?

Sunglasses play an important role in protecting your eyes from potentially harmful UV rays. This invisible form of energy takes the form of radiation which can damage your eyes if they are overexposed. But the pertinent question is, how much protection do I need? Or stated differently, when exactly should I be wearing sunglasses? One of the major determinants about deciding whether a particular situation calls for the use of sunglasses is the environment in which you are in. Rather surprisingly, UV exposure is greater on the snow, as well as on sand, pavement and water, than in more green environments. We often imagine a park at high noon to be some of the most dangerous conditions for UV exposure. But in fact, environments in which your surroundings are reflective, such as snow and water, provide some of the most perilous situations. This is because in such situations, the amount of UV is not easily absorbed by the greenery around you, but rather hits the ground and is reflected back up towards your eyes. This means that you have UV light approaching your eyes both from above and from below. Another dangerous situation, in which you should always be careful to wear sunglasses, is when you are at high altitudes. UV rays are filtered out in the atmosphere. This essentially means that the gasses between you and the sun which are trapped within the earths gravitational pull filter out ultraviolet light before it reaches your eyes. In high altitudes, however, the concentration of those filtering gases, as well as their thickness, is significantly reduced. As a result, light rays are significantly stronger, and thus the presence of UV is much greater at higher altitudes. Time of day, is of course, also one of the greatest determinants of UV risk. UV rays are directed from the sun. As a result, it should seem obvious that the risk of UV exposure is greatest when the sun is strongest, during the hours between 10am and 4pm. At these times the UV rays are more direct and as a result their effects on your eyes are significantly stronger. Consequently, it is key during these periods to take necessary precaution and wear sunglasses when outside. Weather is another often overlooked factor when determining whether or not to wear sunglasses. It seems intuitive that if the sun is out, then UV rays are stronger, and as a corollary, if the day is overcast the risk of UV exposure is virtually nil. This is not the case however. Rather, UV rays quite easily permeate clouds, rain, and the like. This means that an overcast day is no indication that UV rays are any less intense on that day. By contrast, it is often more important to be contentious about wearing sunglasses during such days as we are often not cognizant of the UV risks we are facing and may take risks with our eyes as a result. After learning about the dangers of UV radiation exposure to your eyes the question becomes, not if I should be wearing sunglasses, but rather when should I be wearing sunglasses?