When choosing sunglasses to protect your eyes, the following aspects should be considered:
- UV400 label: Look for sunglasses labeled "UV400". This indicates that the lenses can block 99% or more of ultraviolet rays with wavelengths up to 400 nanometers, including UVA (315 - 400 nm) and UVB (280 - 315 nm). Ultraviolet rays can cause damage to the eyes, such as cataracts, photokeratitis, and damage to the conjunctiva and cornea. Sunglasses without sufficient UV protection may cause the pupils to dilate under the dark - colored lenses, allowing more UV rays to enter the eyes, increasing the risk of damage.
- Appropriate light transmittance: Different activities require different visible light transmittance levels. For general outdoor use, lenses with a light transmittance of 15% - 40% are suitable. For example, if you are driving, lenses with a transmittance of about 18% - 32% are ideal as they can effectively reduce glare while still allowing you to clearly see traffic signs, road conditions, and other details. Lenses that are too dark may reduce visibility, especially in low - light conditions or at night, which is very dangerous.
- Color of the lenses:
- Gray lenses: Gray lenses absorb visible light evenly across the spectrum. They maintain natural color perception, making them suitable for various activities, especially driving, as they accurately represent colors, which is crucial for distinguishing traffic signals.
- Brown lenses: Brown lenses not only block a significant amount of blue light but also provide good color perception. They enhance contrast, making them great for activities like fishing, as they can help distinguish between the water surface and underwater objects.
- Yellow lenses: Yellow lenses are excellent at enhancing contrast in low - light or hazy conditions. They are often used in skiing or shooting, as they can make objects stand out more clearly against a background. However, they are not suitable for bright sunlight as they do not block enough visible light.
- Reduce glare: polarized Sunglasses are highly effective at reducing glare reflected from flat surfaces such as water, snow, and the hoods of cars. Glare can cause discomfort and reduce visual clarity. When light reflects off these surfaces, it becomes polarized horizontally. Polarized lenses have a special filter that blocks this horizontally polarized light, thus reducing glare. This is especially beneficial for activities like boating, fishing, and driving, as it improves visibility and reduces eye strain.
- Optical clarity: High - quality lenses should have excellent optical clarity. Check for any distortion, blurring, or warping by looking through the lenses at a straight line, such as the edge of a door or a window frame. Move the glasses around while looking at the line; if the line appears to bend or waver, the lens quality is poor.
- Scratch - resistance: Since sunglasses are often used outdoors, the lenses are prone to scratches. Lenses with a scratch - resistant coating can maintain their clarity and durability over time. Hard - coated plastic lenses or glass lenses are more scratch - resistant compared to regular plastic lenses.
- Comfort: The frame should fit comfortably on your face without causing pressure points on the nose or ears. Try on different frames to find the right size and shape for your face. The temples should sit snugly but not too tightly against the sides of your head, and the nose pads should support the weight of the glasses evenly on the nose.
- Coverage: The frame should provide adequate coverage to protect your eyes from sunlight coming in from the sides. Wraparound frames are a good option as they can block more peripheral light, reducing the amount of UV rays and glare that reach your eyes from the sides.
