Photochemical effects are associated with wavelengths shorter than which value?

• A. Greater than 550 nm
• B. Exactly 550 nm
• C. Less than 550 nm
• D. 450 nm

Answer: (C)

Photochemical effects occur when photons carry enough energy to drive chemical changes, and photon energy increases as wavelength decreases (E = hc/λ). Around 550 nm lies the boundary where light has sufficient energy to influence chemical bonds; therefore, wavelengths shorter than about 550 nm are associated with photochemical effects. Wavelengths longer than 550 nm have lower energy and are less likely to trigger these reactions. A fixed value like 450 nm is too specific—photochemistry is tied to the threshold at 550 nm, with all shorter wavelengths potentially capable of producing such effects.