Little White Dress -- Not Just for Weddings

White is a color, the perception which is evoked by light that stimulates all three types of color sensitive cone cells in the human eye in nearly equal amounts and with high brightness compared to the surroundings. A white visual stimulation will be void of hue and grayness.

White light can be generated in many ways. The Sun is such a source, electric incandescence is another. Modern light sources are fluorescent lamps and light-emitting diodes. An object that does not alter the color of light reflected from its surface will appear white, compared to the surroundings, unless it has very high specular reflection.

Since white objects such as clouds, snow and flowers appear often in nature, human culture has many references to white, often related to purity and cleanness. The high contrast between white and black is often used to represent opposites. In some cultures, like Chinese, white is considered to be a color that represents death. On the other hand in many cultures white represents purity, freedom, and hygenic purity.

The visible spectrum is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 380 to 750 nm. In terms of frequency, this corresponds to a band in the vicinity of 790?400 terahertz. A light-adapted eye generally has its maximum sensitivity at around 555 nm (540 THz), in the green region of the optical spectrum (see: luminosity function). The spectrum does not, however, contain all the colors that the human eyes and brain can distinguish. Unsaturated colors such as pink, or purple variations such as magenta, are absent, for example, because they can only be made by a mix of multiple wavelengths.

Visible wavelengths also pass through the "optical window", the region of the electromagnetic spectrum that passes largely unattenuated through the Earth's atmosphere. Clean air scatters blue light more than wavelengths toward the red, which is why the mid-day sky appears blue. The human eye's response is defined by subjective testing (see CIE), but atmospheric windows are defined by physical measurement.

The "visible window" is so called because it overlaps the human visible response spectrum. The near infrared (NIR) windows lie just out of human response window, and the Medium Wavelength IR (MWIR) and Long Wavelength or Far Infrared (LWIR or FIR) are far beyond the human response region.

Many species can see wavelengths that fall outside the "visible spectrum". Bees and many other insects can see light in the ultraviolet, which helps them find nectar in flowers. Plant species that depend on insect pollination may owe reproductive success to their appearance in ultraviolet light, rather than how colorful they appear to us. Birds too can see into the ultraviolet (300-400 nm), and some have sex-dependent markings on their plumage, which are only visible in the ultraviolet range.