While UV rays from the sun cannot be seen or felt, they cause irreparable damage, leading to everything from accelerated premature aging to skin cancer to eye damage. In order to help the public with sun protection, the World Health Organization created a scale to help measure UV radiation and confirmed that these levels vary significantly throughout the day.
Early Mornings and Evenings
UV levels are usually relatively low in the early mornings and evenings, although this does largely depend on the location that you are in. If you have outdoor work that needs to be done or want to schedule in some time for a workout or a jog, the early mornings and evenings are usually the best times in which to do this. While sunscreen may still be necessary, other forms of sun protection are likely to not be required, giving you much more flexibility.
Near the Equator
No matter the time of day, UV levels are usually quite high around the equator. This means that constant vigilance about sun protection is necessary, and even more so during the hottest hours of the day.
Your altitude is another factor that influences the amount of sun protection that you need. Those at higher altitudes are exposed to damaging UV rays throughout the day, because not only is the air thinner, but there is less pollution. If you are in a snow-covered area, then the chances of UV damage increase even more, as snow reflects around 90% of UV radiation. In these cases, protective clothing should most definitely be worn, choosing fabrics and styles that are designed to provide the optimum amount of UV protection.
Late Mornings to Afternoons
From around eleven in the morning until three or four in the afternoon, the sun is at its highest point, and its UV rays are at their most harmful. If possible, try to completely avoid the sun during these hours, scheduling indoor activities and tasks. If you do need to be outdoors, then the highest levels of sun protection are needed. This means that not only do you need to apply a generous coating of sunscreen, but you should also be wearing appropriate clothing, a sun hat, and a pair of sunglasses that protect against both UVA and UVB rays.
Tints on Sunglasses
Since the amount of UV radiation can vary so significantly, it is always a good idea to have more than one pair of UV-blocking sunglasses. A darker tint can be used on days when the sun is beaming down, while a lighter tint, but one that still provides 100% UV protection, can be used on cloudier days, when the sun may not be as bothersome but its UV rays still as harmful.
While the time of day has a huge impact on the amount of UV radiation one might receive, there are other factors to also take into consideration, such as your specific location. Many meteorology departments around the world provide information on their websites about UV radiation at different points of the day, and this can be used to ensure maximum sun protection.