UV radiation in this range lies in the long-wave UV spectrum. It is much closer to visible light than UV-C and does not act primarily as a germicidal agent, but indirectly on materials, chemicals, and photochemical processes.

Wavelengths of 365 nm, 375 nm, 385 nm, 395 nm, and 405 nm are commonly used to activate light-sensitive substances, cure plastics, harden adhesives, or serve as excitation sources in fluorescence spectroscopy and sensing. They offer a safe alternative to short-wave UV-C, as they have lower DNA absorption and are therefore less biologically harmful when safety measures are observed.

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Typical mechanisms of action:

• photochemical activation of photoinitiators

• polymerization of resins and coatings

• fluorescence excitation for sensing, detection, and inspection

• enabling material testing and trace detection

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UV-A light is therefore used in many industrial, scientific, and medical applications that do not require primary disinfection but controlled photochemical reactions. Typical application areas include material curing, materials testing, inspection, and medical applications.