Relationship between object color presentation and spectrophotometer

During the day we can see colorful colors, but at night all objects turn black. Relationship between object color presentation and spectrophotometer.
1. Different objects will have different colors, so the color must be related to the attributes of the object itself.
2. In different light environments, the same object will present different colors, such as the apple below. The color is different in light and sunlight, which means that the color is related to the light source:
3. Different people will have different feelings when looking at the same object, so the color presentation is also related to the human eye.

It can be concluded that the color presentation of an object is related to three factors: the attribute of the object itself, the light source and the human eye. As shown in the figure below, when the light source shines on the apple, the human eye can feel the color of the apple.

1. Light source
According to scientific definition, light refers to all electromagnetic spectrum, which can be divided into radio wave, infrared ray, visible light, ultraviolet ray, X-ray γ X-rays are observable objects that produce radiant power, such as the sun, lamps, etc. The wavelength of the light that the average human eye can accept is between 380 and 760 nm.

The sun is the largest light source of mankind. More than 99% of the solar fusion radiation spectrum is between 0.15 and 4.0 microns in wavelength. The solar spectrum distribution is shown in the figure. These bands are affected by atmospheric attenuation to varying degrees. Most of the visible radiation can reach the ground. Most of the ultraviolet radiation is absorbed by the ozone in the upper atmosphere. The solar radiation energy reaching the ground is much smaller than the upper boundary of the atmosphere. The visible spectral area is about 40%, the infrared spectral area is about 60%, and the ultraviolet light content is very small.

Different light sources have different spectral distribution, such as incandescent light, blue light, red light and other different light sources have different component content at each wavelength.

Standard light source uses artificial light source to realize the relative spectral power distribution of CIE standard illuminant to meet the application requirements of colorimetry. Recommended standard light sources are A and C.

Standard light source A: It is realized by gas-filled spiral tungsten filament lamp with relevant color temperature of 2856K. If the relative spectral power distribution of ultraviolet radiation of standard illuminant A is required to be more accurate, it is recommended to use fused quartz glass shell or lamp with quartz window.

Tungsten filament lamp is a widely used artificial light source, easy to use, and widely used by many color measuring instruments. But it is easy to be damaged. At present, some colorimeter enterprises with strong R&D teams have used LED lamps, which use CLEDs (full band balanced LED light sources).

Standard light source C: realized by standard light source A combined with a specific set of Davis-Gibson liquid filters. The filter consists of two solutions C1 and C2, which are respectively installed in a liquid tank made of 1cm thick colorless optical glass.

In practice, the liquid filter needs to be configured very carefully, and its use is also very inconvenient. Therefore, approximate glass filters are often used instead, and of course, all the spectral transmission characteristics obtained cannot be as accurate as expected.

Because the power of standard light sources A and C in the ultraviolet region is very small, which is different from the natural sunlight in which people usually observe the color, the effect is not obvious in the observation of non-fluorescent color, and it can not meet the needs in the observation of fluorescent color. In view of the increasingly widespread use of fluorescent dyes, it is necessary to have standard illuminators including ultraviolet radiation power to approximate the sunlight.

D65 illuminant represents the average sunlight within the visible spectrum, and the short wave is distributed to 300nm. In the area of about 380-300nm, illuminant D65 has a much higher power distribution than illuminant C. The main purpose of D65 illuminator is to calculate the tristimulus value and other chromaticity data of object color by weighting. It can be widely used in textile, printing and dyeing, clothing, leather, shoe materials, plastics, electrical appliances, spraying, electroplating, coatings, inks, pigments, chemicals, printing, packaging, furniture, building materials, photography and other pigment management fields.

2. Attribute of object itself
When light shines on an object, it will transmit, reflect and scatter. When light strikes a transparent object, most of the light penetrates the object, and only a small part of the reflected and scattered light. When light shines on all non-transparent objects, most of the light is reflected and scattered, and almost no light passes through the object. Different objects have different transmissivity, reflectivity, refractive index and other properties for different wavelengths, so they present different colors. The color of transparent objects is determined by the light passing through them, while the color of non-transparent objects is determined by the reflected and scattered light.

For example, the blue sky is due to the fact that when the sun enters the atmosphere, the color light with longer wavelength, such as red light, shines through the atmosphere to the ground; The violet, blue and cyan light of wave length will scatter when it encounters atmospheric molecules, ice crystals, water droplets, etc. Scattered purple, blue and cyan light fills the sky, making the sky appear blue.

When the sky is full of small water droplets after rain, when the sun shines on these small water droplets, light of different wavelengths scatters into the sky at different angles, forming a rainbow.

3. Human eye
The eye is an optical system composed of cornea, iris, lens, ciliary body and vitreous body. The structure of the eye is shown in the figure. The retina with blind spot and macula is the part of light sensing and signal processing, and is the key part of human vision; The optic nerve and brain are signal transmission and display systems. Because light with wavelength less than 300 nm and wavelength greater than 1400 nm can be absorbed by cornea, anterior chamber, lens, vitreous body, etc., the wavelength range of light radiation reaching the retina is 300~1400 nm.

The light reflected by external objects passes through the cornea, pupil, lens and vitreous body in turn, and then falls on the retina through the refraction of lens, forming an object image. There are light-sensitive cells in the retina. These cells transmit the image information to a certain area of the brain through the optic nerve, and people produce vision.

Benchtop Spectrophotometer (Reflectance and Transmittance) DSCD-920 adopts 7 inches touch screen, full wavelength range, Android operate system. Illumination : reflectance D/8° and transmittance D/0°(UV included / UV excluded), high accuracy for color measurement, large storage memory, PC software, because of above advantages, it is used in laboratory for color analysis and communication.

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