Visible light transmission, or VLT, is a measurement of how much light pass through the sunglass lens into you’re eye. If the sunglass lenses has a high VLT, it indicates that the sunglass lenses allow for a lot of light through the lenses. If the sunglass lenses have a low VLT, it means that the lenses block a large amount of light from enter the eye.
Sunglass lenses should be chosen with appropriate VLT level for the environment in which you are wearing the sunglasses; VLT levels that are too low may cause difficulties in environments with low light level. For instance, while it may be tempting to wear sunglasses with very darkley lenses when driving, the darkness of those lenses may make it more difficult to see those driving or walking in the shade. In these situation, sunglasses with Category 2 or 3 lenses are recommended.
How to Pick the Right Sunglasses
However, in high altitudes with snow-covered environments, people recommend sunglasses with Category 4 lenses to block the excess amount of light enter the eyes. The color of sunglass lenses can also alter the way in which you perceive your environment. For instance, sunglass lenses that are gray in color allow color to appear naturaly to the human eye.
Other lenses, such as brown or amber lenses, increase the contrast and depth perception of the wearer. These lenses is helpful for those who drive or hike on trails; the increased depth perception with brown or amber lenses allows the wearer to better perceive change in the road or trail surface. Finally, yellow lenses are used in environments with specific conditions, such as fog or haze.
Because yellow lenses do not block much light from entering the eyes, they are used in situations such as night driving or when driving in overcast condition. Green lenses are often used for activities like golf; green lenses reduce glare and green lenses help the grass to appear vivid. Photochromic lenses are a specific type of lens that change from a clear state to a dark state based off the exposure of the lenses to UV ray.
Photochromic lenses can be convenient for changing the lenses according to the light in the environment, however, the lenses may not work as intended if you are inside of a vehicle. This is because most windshields blocks UV rays, which prevents the lenses from darkening. Additionally, you must decide if you want lens that are polarized or non-polarized.
The measurement of how dark the lenses are not the same than polarization, however. Polarized lenses are a means of managing reflected light; the lenses will block the horizontal light wave that are reflected off of surfaces like water. Thus, if you are often fishing or boating, polarized lenses will help you to see through the surface of the water.
Additionally, you must also consider the difference between VLT and UV400 lenses. VLT measures the brightness of the sunglass lenses, while UV400 measure the protection of the lenses from ultraviolet rays. Thus, lenses can have high VLT rating and still include UV400 protection to the lenses, or lenses can have low VLT ratings and allow the UV rays to pass through the lenses.
Another feature of sunglasses are mirror coating to the lenses. Mirror coatings to lenses help to reflect the light off of the lenses before it enter the eyes, which is helpful in bright sunlight to reduce eye strain. Thus, to select the correct sunglasses for an individual, you must consider the VLT, color, and polarization of the lenses according to the environment in which those sunglasses will be used.
