What is the upper wavelength bound commonly associated with the visible spectrum?

• A. 700 nm
• B. 600 nm
• C. 750 nm
• D. 800 nm

Answer: (A)

The visible spectrum is the range of wavelengths that the human eye can perceive as light and color. The eye’s photoreceptors, especially the cones, respond to light effectively up to about 700 nanometers, with sensitivity fading beyond that. Because of this perceptual boundary, 700 nm is commonly treated as the upper limit of what’s considered visible light; wavelengths longer than this fall into the infrared region and aren’t seen as colors.

Among the options, wavelengths around 600 nm lie within the visible red/orange range, while 750 nm and 800 nm are typically categorized as infrared. So 700 nm best matches the conventional cutoff between visible light and infrared.