Good question-- See the link. Roughly the visible region is 300 nm to 650. so that's 350 nm total. The electromagnetic spectrum goes from 10 Megameters to 1 picometer. So the percentage of the spectrum occupied by visible light is tiny, just 3.5 X 10-9 divided by 10^19 ---- So that's 3.5x10-26 %. So many zeros....! Yikes. Gamma rays (picometers) (10-12)

Hard X-rays

Soft X-Rays

Extreme ultraviolet

Near ultraviolet

Visible light

Near infrared

Moderate infrared

Far infrared

Extremely high frequency (Microwaves)

Super high frequency (Microwaves)

Ultra high frequency (Radio)

Very high frequency (Radio)

High frequency (Radio)

Medium frequency (Radio)

Low frequency (Radio)

Very low frequency (Radio)

Voice frequency (Radio)

Extremely low frequency (Radio) 10 Megameters (10 X 106) Actually the electromagnetic spectrum goes off as far as you want in both directions - there are electromagnetic waves with wavelengths as small as you want, and others as large as you want. So really the answer is 0%. If you meant to ask what percentage of the electromagnetic energy from the sun is visible (for instance) then the answer is nonzero, but I don't know what it is. If you meant to ask a question of the kind that has been answered above (what percentage of the spectrum from 10 megameters to 1 picometer is visible) then the question is not well defined: the answer depends not just on the bounds but on what scale you use. I think the answer above is mistaken. If you go by wavelength, my answer (to that question) would be: 3.5x10-7 divided by 107, which is 3.5x10-14 or 3.5x10-12%. If you use frequency instead of wavelength: The bounds on wavelength given above correspond to 30 Hz to 3x1020Hz, with visible light between 4.6x1014Hz and 1015Hz. Then, the answer would be 5.4x1014 divided by 3x1020, which is 1.8x10-6, or 0.00018%. If you want to use a logarithmic scale, which is more sensible in some ways, then the answer is much higher. I don't know exactly because I don't have a calculator with logarithms here, but it's around 1.5%.