What do people get wrong about sunglass lenses and storage?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Sunglasses are often assumed to protect the eyes in proportion to how dark they are. In fact it is the UV-blocking rate, not the tint, that protects your eyes. Japan has a JIS standard for sunglasses, and knowing how to read its labels changes how you choose. Storage precautions are covered too.
Reading the label (JIS T 7333)
| Label | Meaning | Note |
|---|---|---|
| UV transmittance 1.0% or less (紫外線透過率1.0%以下) | Blocks 99% or more of UV. Japan's JIS label | |
| UV400 | Blocks UV up to a wavelength of 400 nm (international / industry label) | |
| Visible light transmittance (可視光線透過率) | The darkness of the lens. For driving, 8% or more (JIS: under 8% is unsuitable for driving); for night driving, 75% or more | |
| Polarised (偏光) | Reduces reflected glare (water, road surface) | LCD screens can be hard to see |
| Photochromic (調光) | Tint changes with the amount of UV | Changes little inside a car (UV-cut glass) |
- JIS T 7333 (sunglasses) specifies labelling for UV transmittance, visible light transmittance and suitability for driving, among other things. Even with cheap fashion sunglasses, check for a JIS label or a "UV cut" (UVカット) label.
- The Ministry of the Environment's "UV Environmental Health Manual" lists risks such as cataract and pterygium (a growth on the surface of the eye) from UV, and recommends UV-blocking sunglasses and a hat. A shape that fits the face closely and blocks light from the side is effective.
- Plastic lenses are heat-sensitive (around 60°C); left on a car dashboard, the coating cracks and the lens warps.
[Verify] Check the labelling items and figures in JIS T 7333, and the wording of the Ministry of the Environment manual.
Misunderstanding 1｜The darker the lens, the better it protects
UV protection has nothing to do with tint. A dark lens without UV protection opens the pupil and lets more UV in, so it is worse. Look for "UV transmittance 1.0% or less" or "UV400" on the label.
Misunderstanding 2｜Cheap sunglasses don't block UV
Regardless of price, if it is labelled, it blocks UV. The differences are lens distortion, durability and frame quality. Avoid unlabelled ones.
Misunderstanding 3｜Any sunglasses will do for driving glare
Visible light transmittance under 8% is unsuitable for driving (JIS). Dark lenses are dangerous at night and in tunnels. Polarised lenses can make the sat-nav screen hard to read.
Misunderstanding 4｜Keeping them in the car is handy
A car interior in summer reaches 60–70°C, cracking the coating on plastic lenses and warping the frame. Take them with you, in a case.
Misunderstanding 5｜Wipe the lenses on your shirt
Dust scratches them and the coating peels. As with spectacles, rinse with water first, then use a lens cloth (see the glasses-care article). Don't put them in the case lens-down.
---
Sources
- Japanese Industrial Standards Committee (JISC), JIS T 7333 "Sunglasses, sun visors and fashion spectacles" [日本産業標準調査会 JIS T 7333「サングラス、サンバイザ及び眼鏡ファッション用」]
https://www.jisc.go.jp/
- Ministry of the Environment, "UV Environmental Health Manual 2020" (effects on the eyes and sunglasses) [環境省「紫外線環境保健マニュアル2020」]
https://www.env.go.jp/chemi/uv/uv_manual.html
- Japan Federation of Optical Industry Associations, "How to choose sunglasses" [日本眼鏡関連団体連合会「サングラスの選び方」]
https://www.megane-japan.or.jp/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
Follow the care label and the maker's instructions for any garment, shoe or bag. For expensive or sentimental items, ask a specialist cleaner or repairer.
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