That portion of the electromagnetic spectrum visible to the human eye, having a wavelength in the range from about 4,000 (violet) to about 7,700 (red) angstroms and may be perceived by the normal unaided human eye. It ranges from the red end to the violet end of the spectrum, with wavelengths from 700 to 400 nanometres and frequencies from 4.3 x 1014 to 7.5 x 1014 Hz. Like all electromagnetic radiation, light travels through empty space at a speed of about 186,000 miles per second (300,000 km/sec).