Visible light is a type of electromagnetic wave with a wavelength ranging from 380 to 780 nanometers, corresponding to the electromagnetic spectrum detectable by the human eye. Optical radiation within this wavelength band is defined as the visible spectrum, simply referred to as light. For people with normal vision, the detectable wavelength range of visible light falls roughly between 380 nm and 780 nm. Outside the red end of the visible spectrum lie numerous invisible spectral bands, including infrared rays, microwaves, ultraviolet rays, X-rays and more, all of which cannot be perceived by human eyes.

Visible light consists of seven spectral colors: red, orange, yellow, green, blue, indigo and violet. Sunlight serves as a natural light source, whose spectral range covers 0.38 to 0.78 micrometers. Artificial light sources are categorized into two main types: thermal radiation light sources such as incandescent lamps and iodine-tungsten lamps; and gas discharge light sources including fluorescent lamps, high-pressure mercury lamps, xenon lamps, metal halide lamps and lasers.

The human eye has varying sensitivity to electromagnetic waves of different wavelengths, and can only sense those within the 380–780 nm range, which we name visible light. Visible light of different wavelengths presents distinct colors. For instance, red light has a wavelength of 625–740 nanometers, while violet light ranges from 380 to 450 nanometers.

In summary, visible light is the segment of the electromagnetic spectrum perceivable by human vision, covering red, orange, yellow, green, blue, indigo and violet, with a wavelength span of 380 to 780 nanometers.

As a form of electromagnetic radiation detectable by human eyes, visible light occupies the visible region of the electromagnetic spectrum, with wavelengths approximately from 380 nanometers (the boundary of ultraviolet light) to 740 nanometers (the boundary of infrared light). It encompasses a full range of colors including violet, blue, green, yellow, orange and red.

Cone cells in the human retina respond differently to various wavelengths of visible light. Arranged by increasing wavelength, the corresponding colors are violet, blue, green, yellow, orange and red. Mixing visible light of different wavelengths can generate a wide variety of additional colors and shades.

Being the most prevalent form of light in daily life, visible light enables us to perceive the surrounding world, and also acts as one of the primary constituents of natural daylight and indoor illumination.