A substance, product, or agent that makes something brighter, lighter in color, or more luminous, such as optical brightening agents in detergents or teeth whitening products.
From brighten (Old English beorht 'bright' plus -en, making a verb) plus -er, creating an agent noun. The -er suffix indicates something or someone that performs the action of the root word.
Optical brighteners in laundry detergent don't actually make clothes cleaner—they use fluorescent chemicals that trick your eyes by bouncing ultraviolet light, making white clothes glow unnaturally, which scientists call 'optical illusions you wear.'
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