Reactive lenses, also known as photochromic lenses, work because of a chemical reaction that occurs when they're exposed to ultraviolet (UV) light, like that found in sunlight. This reaction causes the lenses to darken.
Here's a breakdown of the process:
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Special Molecules: The lenses contain microscopic crystals of silver halide (usually silver chloride) embedded within the lens material. These crystals are transparent and evenly distributed, making the lenses clear in normal indoor lighting.
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UV Light Activation: When UV light hits the lens, it provides energy to the silver halide crystals.
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Chemical Reaction: The UV energy causes the silver halide crystals to undergo a chemical reaction. Silver ions are reduced to silver atoms, and halide ions are oxidized. This process results in the formation of tiny clusters of metallic silver.
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Light Absorption: These clusters of silver atoms absorb a portion of the visible light spectrum. The amount of light absorbed depends on the number and size of the silver clusters. The more UV light, the more silver clusters form, and the darker the lenses become.
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Reversal of Reaction: When the UV light source is removed (e.g., when you go indoors), the chemical reaction reverses. The silver atoms recombine with the halide ions, and the silver clusters disperse. This causes the lenses to gradually return to their clear state.
In summary, reactive lenses contain light-sensitive molecules that change their structure and light-absorbing properties when exposed to UV light, causing the lenses to darken. The effect is reversible, and the lenses return to their clear state when the UV light source is removed.
