Since this is wintertime and you are shovelling snow on the bright snowy day clearing the driveway and the sidewalk. You spend some time outside, longer than usual, just staring at the snow. This season has something in common with the summer. It can be very bright outside. Some people might find it too bright, too.
Around wintertime snow blindness occurs when you are outside for too long with poor eye protection. The rays from the sun hit your eyes and vision may become distorted, blurred and colours may become weird too. Sometimes the snow might shift from white to light red if you are outside during the very sunny hours. The UV rays hit the snow doubling the amount of infrared light that your eyes would be consuming. The glistening snow might actually damage your eyes if you are not well prepared.
Snow blindness is a common form of photokeratitis. Too much UVA rays are beaming into your eyes making it hard to see. The snow can reflects around 80% of UV radiation from the sun making the glow brighter. You can also accidentally get a sunburn in the winter with this condition by burning the corneas in your eyes. The eyes would feel like sand got in them but they might be really irritated. Also tearing and not wanting to open the eyes. It’s not just from prolonged exposure in the snow, it could be caused by welding, tanning beds, floodlight and halogen lamps or light reflecting from large bodies of water or sand.
Glare can be extremely annoying and dangerous because you can’t see everything in front of you. A late-night snowfall could result in a morning of snowy roads and an afternoon of glaring snow. Eye strain, blurred visions, pain, temporary blindness and headaches are conditions that might be suffered in extremely lit places. When light bounces off the clean snow, it can create a light-induced “whiteout” of the area.
The amount of light the snow casts out is called the albedo. This is a non-dimensional and unitless quantity that measures how well the surface reflects solar energy. It is a range between 0 to 1. Zero means a perfect absorber which is incoming energy absorbed. For example, in the spring when the grass is green the albedo would be at 0.25 or 25% of the solar energy is being reflected. While one means a perfect reflector of incoming energy is reflected and not absorbed. The brightness can depend on the depth of the snow.
Fresh snow can be very bright when it first falls because it may not have any impurities like dirt, acid or soil to lessen the brightness of the powder. When the snow is sparkling, that’s the light from either the sun or other light source bouncing off of the snowmaking it glisten. The freshly fallen snow can glisten at 95% versus older snow at 80%. The brightness amount that a person might experience might come from the angle that are standing at.
Light rays from a particular angle would diffuse in multiple directions. Ideal diffuse reflection from light would obey Lambert’s cosine law. This law is when the intensity of light of either the luminous or the radiant is at the angle of θ between the direction of light and the surface. Snow is not always a Lambertian surface but it sometimes can come close. A snowy surface can be brighter than the sky because the illumination of the snow requires integration over the hemisphere. The Mach bands will cause further brightness or haloing of the snow.
Mach bands are based on lateral inhibition. Lateral inhibition is a process of light collected by retina cells is affected by the collection of light near neighbouring cells. This helps boost the perception of object edges. This makes it easier to see the edges of an object would go unnoticed. Mach bands are visual optical illusions that the eyes and the brain perceive has low-light and highlight.
Wearing sunglasses that protect you from UV rays can do the trick and not staying outside for too long. It’s a great shield to block out the snow, ice and wind. Therefore, your eyes are protected from large immediate objects flying close to your face. Most sunglasses already block out UVA, UVB and UVC rays from the sun. We think about these rays in the summertime, which is good, but rarely associate those rays around wintertime. Wearing sunglasses would block out harmful rays but help retain good eye health.
There are many types of sunglasses available and historically been around. In most communities near the Arctic like the Inuit people and the Yupik people have snow goggles (ilgaak) that are made out of the bone of an animal carved into a slit that wraps around the eyes. They were traditionally made out of spruce driftwood but caribou antlers or walrus ivory were once used. They were worn for outdoor activities like hunting, fishing or travelling across the snow. They wore these goggles to prevent snow blindness almost back to the 12th century.
Photochromatic lenses are transition lenses that darken when ultraviolet light is reflecting off of the glasses. This is the newer version of the glasses available. This provides a smooth transition from indoor light to shades if the wearer needs glasses to see but there are different types of glasses for everyone else.
There are sunglasses that have a coating which reduces glare. Polarized lenses block horizontal light waves (reflections) which cause glare but allows vertical light waves (direct light) through. Most polarized lenses are 100% UV protection.
The type of lens colour needed depends on the conditions. This table is based on skiing lenses. A rough outline of colour shades and the conditions are listed below.
|Clear||Extremely Low Light, Nighttime|
|Black / Dark Grey||Very Bright Light|
|Yellow||Flat Light, Can Filter Out Snow Brightness and Blue Light|
|Amber / Orange / Copper||For Overcast, Sunny Days, Foggy|
|Brown / Bronze||Good Amount of Light|
|Pink / Rose||Low to Mid Light, Overcast, Partly Cloudy|
|Red / Vermilion||Medium to Bright Light|
|Violet||Low to Moderate Light|
|Green||Low Light, Maybe Overcast|
For more facts about snow: