Visible wavelengths make up about one-half of the electromagnetic spectrum?

Answer 1

Nope.

-- Visible light has frequencies roughly from 4 x 1014 Hz to 8 x 1014 Hz ... a

range from lowest to highest of 4 x 1014 Hz, or one octave.

-- Let's say that the lowest frequency in the total spectrum is 50 Hz (European

power-line frequency) and the highest is 1019 Hz (lowest freq gamma rays) ...

a total range from lowest to highest of (1019 - 50) Hz, or about 57 octaves.

-- On a linear scale, of the total number of Hz in the spectrum, visible light

covers about 0.004 percent of them.

-- On a logarithmic scale, visible light covers 1 octave out of 57 octaves,

or 1.74 percent of the spectrum.

Answer 2

Yes, visible wavelengths range from approximately 400 to 700 nanometers in the electromagnetic spectrum. These wavelengths correspond to the colors we perceive in the rainbow, from violet at around 400 nm to red at around 700 nm.