Spectral color

A spectral color is that color impression, to generate a selected one of the visible part of the spectrum monochromatic light. It is available in any color the most intense, thus pure color.

Although it is theoretically an infinite number of spectral colors, in daily contact with them is often only from a certain relatively small number of spectral speech, for example, of the seven rainbow colors of red, orange, yellow, green, blue, indigo and violet. You are not closely selected from the spectrum of light, in the best case, all slightly different colors depending on a range of wavelengths are meant and the wavelength ranges abut one another without gaps.

Spectrum

The spectrum ( as a concept of color theory ) is the set of all lines and bands of a certain frequency. "White light" in the physical sense ( and practically hardly feasible ) from shares of all wavelengths of the visible spectral energy equal to mixed light. Mostly, it refers to natural light (sunlight ) and the standard light types with their different color temperatures. The color sensation produced by an equal-energy light source means exactly enough, " achromatic ".

By refraction at optical prism through diffraction gratings or interference succeeds in " white light " to be divided into spectral colors. Spectral colors as monochromatic light can also directly arise (sodium vapor lamp, laser) with appropriate emission processes. Newton put these facts in his Opticks dar. He named seven spectral colors, namely red, orange, yellow, green, blue, indigo, violet, without definitively assign them a wavelength or a wavelength range.

Particular importance is attached to the "white radiation ", ie the equal-energy radiation in the photometry and related fields. Here it is important to achieve the necessary ( observed ) wavelength intervals this property. For the measurement of the eye sensitivity curve in addition to the equal-energy radiation even a quantum of equal intensity radiation is required. Such measurements are used to derive Normspektralfarbwerten.

Colorimetry

In order to display a three-dimensional color space, the color stimulus of the wavelength spectrum is mapped onto the three ( color sensitive ) cone types sensors types. For this, a suitable system of color stimuli to set up the primary colors of the red, green, blue sensitivities. The calculation rule for this is standardized with the Tristimulusalgorithmus since 1931. Required parameters were refined in later studies and confirmed in principle. The result in the graph is the " shoe sole curve" the standard color chart, called chromaticity.

The spectral colors lie on the circumference of this surface. The spectral colors are so gesättigsten the colors of the dominant wavelength.

A dependence of the color coordinates of the perception is due to the different position of the Spektralkurvenzuges, depending on whether the 2 ° field of view or a 10 ° field of view will be used. Within the 2 -degree field is imaged on the retina surface of the " best color vision ," in the retina are the pins here closest together. In the 10 ° field of view, the density of cones decreases already and there is added the sensation of chopsticks. This field corresponds to an A4 sheet in normal viewing distance.

Color perception

The cone cells in the human retina (as well as other creatures ) have different sensitivity depending on the type of spectra that cover specific areas of the received light spectrum. The processing of data originating from the pin signals converts the received light of different spectral and intensity into perceived colors. Since the weighting of the spectral components depends on the perceptual areas of the cone types, even the perception of color is directly dependent on it. If some of LEDs a nearly monochromatic light presented, this light color is perceived as a very pure ( saturated) and bright, so as spectral color. In the case of human vision there is no light spectrum that excites only a single type of cone. Since the areas of the cone types overlap, several types are always addressed simultaneously.

The spectrum locus CIE is supplemented in the chromaticity diagram with the purple lines, but containing mixed colors. Physically, there is no corresponding spectral for purple tones. This can only be seen on a mixed perception of short-and long-wavelength light. In the CIE diagram corresponds to the purple tones with the highest saturation this purple line. In principle, all non- spectral colors mixed colors.

The human color perception in daylight vision ( photopic vision) is limited to three types of receptors for short, medium and long wavelengths. Some animals, especially birds, such as pigeons, have four color receptors. This allows them to distinguish more colors and types of paint than a man. Other species, such as dogs, have only two types of color receptors. This leads to a smaller amount of distinguishable colors.

At the long-wavelength red end of the visible spectrum is the region of the invisible infrared light borders. Due to the continuous transition in sensitivity to irritant wavelengths, this limit is fluent ( between 720 nm and 830 nm) and is subject to individual variation. This is mainly determined by the chemical structure of rhodopsin ( visual purple ). The perceived color changes only slightly from 650 nm.

The infrared region of the spectrum is referred to as thermal radiation, although each absorbed electromagnetic radiation generates its energy equivalent as heat, whether it is long -wave radio emission or hard (very short wavelength ) gamma rays. The heating effect of infrared and radio radiation is perceived by people directly through other receptors. The penetration depth of the radiation in turn is dependent on the wavelength. Near infrared radiation penetrates only a few millimeters into the body, a radio radiation is converted in the body. This effect is used in the short-wave radiation to heat the internal organs.

The short-wavelength violet end of the visible spectrum, at wavelengths from about 380 nm and smaller, is adjacent to the range of ultraviolet light. These wavelengths do not cause any irritation to the human receptors therefore is ultraviolet light invisible. For the same reason as in the infrared end of the light spectrum, the visibility of the radiation between 360 nm and 410 nm is individual and age-related inferior fluctuations, even more than in the infrared region near. The pigmentation of the cornea plays a big role here. In addition, the lens turns yellowish with increasing age, causing short-wavelength light is more filtered.

In cataract surgeries after removal of the clouded lens, the filter effect is removed ( aphakic vision), which leads to a marked improvement in the perception of short wavelengths. After inserting the plastic lens of this special effect is canceled.