How can ultraviolet light affect certain dyes or inks?

• A. It renders them invisible.
• B. It causes them to heat and change color.
• C. It enhances their fluorescence for visibility.
• D. It disintegrates them completely.

Answer: (C)

Ultraviolet light can enhance the fluorescence of certain dyes or inks, making them more visible. This occurs because many dyes and inks contain compounds that absorb UV light and re-emit it as visible light, a phenomenon known as fluorescence. When exposed to UV light, these compounds can reflect additional colors that may not be visible under normal lighting conditions, thus increasing their brightness and visual appeal.

This property is particularly useful in various applications, such as in security inks used in banknotes or identification documents, where the presence or absence of fluorescence under UV light can help verify authenticity. This interaction between UV light and specific dyes or inks showcases the significance of fluorescence in enhancing the visibility and effectiveness of these materials in practical uses.