UV400 lenses are designed to protect the eyes by blocking ultraviolet (UV) radiation up to 400 nanometers (nm), which includes both UVA (315-400 nm) and UVB (280-315 nm) rays. The way these lenses block UV radiation can involve a combination of absorption and reflection, depending on the materials and coatings used.
Mechanisms of UV Blocking

    Absorption:
        Material Composition: UV400 lenses are often made from materials that inherently absorb UV radiation. For example, polycarbonate and certain types of plastic and glass used in eyewear have properties that absorb UV rays. The molecules in these materials are structured in such a way that they can capture and dissipate the energy from UV light, preventing it from passing through the lens.
        UV-Absorbing Additives: Some lenses incorporate special UV-absorbing compounds or dyes during manufacturing. These additives enhance the lens’s ability to absorb UV radiation. When UV light strikes the lens, these compounds absorb the energy and transform it into a harmless form, usually heat, which is then dissipated.

    Reflection:
        Surface Coatings: Some UV400 lenses have reflective coatings on their surface that reflect UV light away from the lens. These coatings can be metallic or multilayer dielectric coatings that are specifically engineered to reflect UV wavelengths. By reflecting the UV rays, these coatings prevent the harmful radiation from entering the eye.
        Anti-Reflective Layers: These are additional layers applied to the lens that can also help to minimize the amount of UV light that passes through by reflecting it away from the surface.

How They Work

    Layer Construction: UV400 lenses often consist of multiple layers, each serving a different function. A base layer of UV-absorbing material is combined with surface coatings that provide additional reflective properties. This multi-layer approach ensures comprehensive protection against UV radiation.
    Molecular Interaction: On a molecular level, the UV-absorbing materials in the lenses contain chromophores, which are parts of molecules responsible for absorbing certain wavelengths of light. These chromophores capture the UV photons, causing their electrons to jump to a higher energy state. This absorbed energy is then released as heat, effectively neutralizing the harmful UV rays.

Summary

In essence, UV400 lenses protect the eyes through a combination of absorption and reflection. The materials used in the lenses absorb UV radiation, while special coatings reflect additional UV light away from the lens surface. This dual mechanism ensures that UV rays do not reach the eyes, thereby preventing potential damage such as cataracts, macular degeneration, and other UV-induced eye conditions.