What is the wavelength range of UVA light?

• A. 280-320 nm
• B. 400-450 nm
• C. 320-400 nm
• D. 180-280 nm

Answer: (C)

UVA light consists of the longest-wavelength portion of ultraviolet radiation, sitting just before the visible spectrum and ending around 400 nm. In many references it’s defined roughly as 320–400 nm (some sources use 315–400 nm). This longer-wavelength UV is ideal in penetrant testing because dyes excited by UVA emit visible fluorescence, making flaws easy to detect under UVA lamps. Among the options, 320–400 nm falls squarely in this UVA range; 400–450 nm is visible light, 280–320 nm is UVB, and 180–280 nm is UVC.