Kandratsky proposed a differential photometer
1), this photometer is mainly used to measure the reflectance of achromatic color surfaces (white, gray and black). If a filter is used, this instrument can also be used to measure the color of faintly colored surfaces with close accuracy. The principle of action of the Kandelsky photometer is similar to that of the semi-obscuration 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 a small box and place it in the left chamber of the photometer (when measuring the color of dry paint, spread the sample on the metal plate with the edge rolled up, and then use the glass plate to spread the paint 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 for the left and right sides are recorded on two separate lines. Determine the millimeters of the size of the small window on the right by the reading. Because the sum of the left and right small window gaps is a constant, it always equals 50mm, 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 Kondracki photometer to measure, use a lighting (100-200 watts) as the light source, and the lighting device is in the dark glass or vertical direction with a distance of about 40cm. Behind the lamp, it is recommended to install a reflector painted white.
