7.4.3—That wavelengths in the range 400–700 nm in free space are visible to the

The visible band is approximately 400–700 nm in free space, from shorter-wavelength violet to longer-wavelength red.

Treat the limits as approximate and use wavelength/frequency trends when identifying colour or neighbouring ultraviolet and infrared.

A 500 nm wave lies in the visible range, while 350 nm is ultraviolet and 900 nm is infrared.

Visible colour is not determined by intensity alone; wavelength sets the nominal colour while intensity affects brightness.