1. Determination of color with a differential photometer
This photometer is mainly used to determine the reflectance of achromatic colored surfaces 7 (white, gray and black). If a filter is used, this instrument can also be used to measure the color of faintly colored surfaces with near accuracy. The principle of action of the Kandelaktite photometer is similar to that of the bovine obscura photometer. The determination of the reflectance of white and gray surfaces consists in determining the intensity of the light flux. In the case of other conditions being equal, the intensity of the luminous flux is proportional to the area of the hole through which the luminous flux (luminous flux) passes.
Put the colored thick paper or white iron plate in the cell and place it in the left chamber of the photometer (when measuring the color of the dry pigment, the sample is withdrawn from the metal plate with the edge rolled up, and then the pigment is covered with a glass plate. smooth the surface).
Place a standard color sample in the right chamber; then turn the screw head to adjust the position of the movable curtain; measure the size of the gap; measure the intensity of its luminous flux on the scale.
Then, change the standard color sample and sample in some places, and measure the size of the gap at the curtain position again. The measurement must be carried out 2 to 3 times. The readings on the left and right sides were recorded separately for westbound travel.
The reading determines the size of the gap in the right small window in millimeters. Because the sum of the left and right small window gaps is a constant, always equal to 50 millimeters, so the size of the left small window gap can be determined by subtracting the gap size of the right window from 50.
When using the Kandela sub-photometer to measure, the electric lamp (100~200 pentex) is used as the light source, and the electric lamp is installed in a direction perpendicular to the dark glass at a distance of about 40 cm. Behind the lamp, it is better to install a reflector painted white.
The reflection coefficient is calculated according to the following formula:
2. Determination of color with graded photometer
A schematic diagram of the graded photometer 3 is shown in FIG. 2 . The optical component of this instrument is a monocular telescope installed at an indeterminate distance. There are two objective lenses 1 and 2 inside the telescope. The light beam to be compared is transmitted into the telescope through these two lenses. The distance between the two lens axes is 70 mm. The light beam passes through the connecting mirrors 3 and 4 and the double button mirror 5 . Through the small-sized magnifying glass on the device eyepiece 6 again, the reflections of the aperture 7 and 8 that cover each other can be clearly seen, which is the adjusted "exit pupil".
If viewed through an eyepiece without a magnifying glass, two semicircles divided by a fine line can be seen. Other things being equal, the relative brightness of the semicircle depends only on the ratio of the open areas of the two lights.
The measurement of color (including white and black) is carried out using light-transmitting filters and blocking filters. When using a light-transmitting filter, compare the luminosity of the sample 9 with the standard silver plate 10, and the chromaticity of the black color contained in the sample can be obtained. When the retention filter is used, the chromaticity of the contained white color can be measured by the same method.
Place the device for inserting various filters in front of the photometer eyepiece. There are seven filters (seven colors) in the messenger. The color containing white is characterized by the smallest spectrum (in the darkest part of the spectrum), so if the color contains white, it must be measured with an optical filter (retention filter) with the smallest measurement value. The feature containing black has the largest spectral curve, so it is necessary to use the filter with the largest measurement value (light-transmitting filter) for measurement.
Color-like colors can also be measured using a grading photometer.
