A color temperature is a characteristic of a light source that makes it possible to evaluate its color. This is a simple and visual parameter, despite the vague definitions set forth by official science. It seems that it is impossible to link the temperature and color, but experienced blacksmiths know that it is already permissible to forge a dark cherry blank. The text below explains in detail how physicists came to this curious interpretation.
Radiation spectrum and physiological features of the eye.
To fully understand the topic, let us familiarize with the concept of the locus of colors. This figure, reminiscent of a bent to the left and inverted parabola, massively found in the literature. No explanation is given for the submitted image. Meanwhile, the color schemes used in television and printing are not taken from the sky. Always people proceeded from reality.
According to scientists, people owe sight to two types of receptors: rods and cones. Moreover, the former are not interested today, they are involved exclusively in the dark and do not perceive colors. It has been experimentally established that three types of cones are distinguished:
- Long-wave.
- Medium wave.
- Shortwave.
Based on the work of two scientists, David Wright and John Gilda, in 1931 the first model of flowers was created. It closely correlated with the physiological features of the human eye, which is often overlooked in specialized literature. The visible spectrum, distinguished by most people( color blindness does not count), is limited from the low-frequency section to red, and from the high frequencies to purple. In the middle are yellow and green. So, by experience, we found that:
The model of flowers by David Wright and John Gilda
- Long-wave cones of the eye exhibit a maximum sensitivity in the region of 600 nm. It is close to red. Biological sensors have a second peak, now around 450 nm. Which is close to purple color.
- The sensitivity of the mid-wave is located approximately in the center. There, in the region of 550 nm, is green.
- Shortwave cones better perceived purple color. Detect the maximum( in amplitude) sensitivity.
These patterns formed the basis for the creation of a locus, then into RGB, CMYK and other systems. Colors exist only in the mind of man. In the physical world, this is simply a certain emission spectrum. If we talk in detail, this area accounts for less than 0.04% of the optical range. The spectrum of radio waves, X-rays and gamma rays take up much more space. But for a man, 90% of the information is obtained through the visual channel.
From what has been said it follows that the sensitivity of the eye to frequencies is not the same. For example, seeing ultraviolet light is not given to anyone; individual psychics observe an aura. On average, the sensitivity of the eyes of any person fluctuates around the medium-sized bell-shaped graphs with peaks, the coordinates of which are indicated in the list above. Printing, television and other related industries are oriented to the majority of the population. And get to the point.
In the course of the research, it turned out that the colors that satisfy the Kruithof curve, which do not cause pain and harm to a person, lie within a cone with a sole in the form of a horse's hoof. On three axes, the effect of radiation produced on the previously mentioned types of cones is postponed. It is difficult for a person at the moment of the development of history to operate with three-dimensional figures, therefore the distribution of colors has been optimized for the plane. The form is slightly distorted, but the perception is simplified. Entered values:
Temperature range
- X - the intensity of the glow of the low-frequency part of the spectrum. Graph in the literature of red color, to once again emphasize the location( see above about the boundaries of the visible range).As already noted, a part of the violet flow enters into these “gates” to a relatively small degree.
- Y - calculated for the middle part of the spectrum; on the graphs it is depicted green.
- Z - similar, but for the upper part of the spectrum. Color - blue.
All three quantities are recognized as integral, calculated over a range of a certain length along the frequency axis( abscissa).Represent the product of the sensitivity of the corresponding type of cones on the power flux density of the radiation source in this area. About close connection with physiology noted above. Thus, the CIE1931 color system adopted in 1931 reflects the characteristics of an object and the ability of cones to receive radiation. According to this concept, two coordinates are taken - X and Y - each includes the total luminosity of the body, Z is taken into account indirectly( see the figure from Wikipedia).
In the formulas, the Greek letter lambda denotes the wavelength, and I is the luminosity of the body( spectrum).Recall that x, y and z characterize different types of cones of the human eye. Now let's talk about the connection with color temperature.
Absolute-blackbody
by Hilbert in 1912 proved that in a state of thermodynamic equilibrium, the radiation of an absolutely blackbody satisfies Kirchhoff's law( see fig.).Approximately the atmospheres of most stars are suitable for this occasion. It becomes possible to determine their approximate temperature( and even temperature field) by performing a spectral analysis. Briefly: an absolutely black body radiates a maximum of the power density, which is determined according to the Wien displacement law, which in the current interpretation indicates the location of the peak. This frequency, which is the “top of the mountain” on the graph, is directly related to temperature( in kelvins).
Kirchhoff's Law
The luminosity spectrum of an absolutely black body is perceived in a certain way by the eye. For each temperature, it is unique, and readers have already guessed that this is considered to be the true definition of the value considered today. Due to the superposition of the fields( all the colors of the visible range), a certain average is obtained that is uniquely displayed on the locus. In the picture taken from Wikipedia, the location of the points is displayed as a curved dark line. The notches indicate the color temperature.
The dependence of the spectrum on temperature and the effect of the parameter on human circadian rhythms
It has been established that blue stars are hotter than red ones, and the Sun is in the center, satisfying the average. Today, according to science, our star has gone about half the way of development, which will result in the transformation into a white dwarf. Based on the results of research, conclusions were drawn about the lifetime of the solar system, close to 5 billion years. For any color temperature, connoisseurs make poetic comparisons that lead an unsophisticated novice to a dead end. For example, it is said that the value of 5000 K corresponds to the light of the Sun, which is at its zenith, and 9500 K corresponds to the sky on the northern side of the horizon at sunrise.
The question immediately arises - what happens brighter than the sun at its zenith. The essence comes down to color. Just that color would have had hotter stars than the sun. In the classification, the northern side of the sky was higher. But its power flux density is relatively small, it will not blind the eye. Therefore, choosing a light bulb in the store, do not think that the increased color temperature will give more sense. The parameter value is not intended to characterize power.
Temperature Spectrum
Another example: a distant hot blue star at night in the sky is no brighter than a firefly. Although if you approach the star at a short distance, the result would be predictable. For a person in the daytime, the color temperature of 5000 - 5500 K is considered optimal. And it makes no sense to choose a light bulb with a large value, except for decorative reasons. By the way, the question under consideration is closely connected with the concept of color rendition: a person feels cozier, lit by the natural rays of the Sun. Everything else seems unnatural or frightening. For this reason, DRL lamps with corrected parameters appeared on the light.
It has long been proven that illumination affects biorhythms. It is established that the adjustment of organisms goes in a certain interval. Biorhythms do not emit precise periods, but the values vary within certain limits. On the subject of illumination, there is a rule of Ashoff, which states that circadian rhythms are accelerated in night animals in the dark. Paradox - in humans, under similar conditions, the opposite is true. For proof, the professor placed in a dark apartment two sons( 1962).Later it turned out that the sleep-wake cycle was extended for half an hour compared to the usual one.
Science knows that the growth hormone is most intensively produced from 23.00 to one in the morning. And the time being taken is local! Not Moscow, not regional, but geographical. Thus, circadian rhythms set the period of sleep and wakefulness and other important points.
For example, if an athlete does not follow the schedule for the day, muscle growth will certainly slow down. At the beginning of the 60s, active studies of circadian rhythms are not accidental. Then mankind realized that laws in space are different. For example, the well-known newspaper Speed-info published a note that under weightless conditions the reproduction function is lost. Protection against waste of resources?
Highlights and beneficial effects. Chickens with the help of exposure to light in a certain way are forced to rush overtime. After the disappearance of the external factor, circadian rhythms are briefly preserved, due to inertia, and received the name( Latin Circa - approximate).It has been empirically established that by varying the lighting, it is easy to change the phase of some processes. For example, to cause sleep after midnight or during the day. At the same time, the period remains almost unchanged. Maximum deviations correspond to 18 and 30 hours: for hamsters, for example, 21-26 hours.
However! In extreme positions, dissynchronization of individual circadian rhythms of a single organism was observed. For example, it is possible to attach isopods crayfish, the color( pigmentation) of which appeared unnatural. It has been established that continuous exposure to bright light becomes especially unfavorable for circadian rhythms. It is now clear, in addition to these factors, light affects the alpha rhythms of the brain. Color temperature can enhance or slow down performance. It should be preferred for the bedroom values up to 3000 K. This color temperature corresponds to a warm, yellow shade. Intensity is not meant to be too high.
In order to maximize the efficiency of vital activity, stimulation with sound and light factors during the waking period is possible by varying the color temperature. This is especially important where much depends on the quality of the actions performed. In particular, space projects have already been mentioned. Of course, we are not able to provide specific recommendations, most of the data is classified. But it is known, for example, that during interrogations a continuous bright light striking the eyes is used, and the terrorists are periodically treated with infrasound. And color temperature plays an important role.
