The standard “Volvo STD 423-0041 Color assessment in the light booth” developed by the Volvo car company describes a subjective method for visually comparing colors with color master samples. When applying this method, the test piece (a colored or painted part or panel) is placed next to a color master sample and colors are visually compared under light sources of different wavelengths.
The described method is valid for colored materials, especially for:
This method can be used for the following purposes:
Light from the various light sources used in the tests is filtered through a dispersive screen that does not change its spectral characteristics. Relative spectral power distributions for light sources are included in the standard annex. Namely,
The light cabinet should be placed in a room protected from external light. The evaluation area should be protected from extraneous light, reflections and other objects that may affect visual evaluation.
The approximate dimensions of the light cabinet and the approximate dimensions recommended for positioning the light cabinet on a horizontal table surface are shown in the figure given in the standard.
The test piece substrate and surfaces (floor, walls, ceiling) within the light booth should be a matte neutral gray color. The color corresponds to Munsell N60 with a brightness not exceeding 15 brightness units at 7 degrees.
Light sources must be cleaned regularly, at least every three months. The operating times of the light sources must comply with the limits specified by the manufacturer. The emission characteristics must be checked and adjusted by the manufacturer at least once a year. Lamps for a given light source must always be replaced in pairs (if one lamp is worn, both must be replaced).
One light booth that meets the requirements of this standard is the Macbeth Spectra Light.
The observer's color vision should be checked medically to ensure that the person in question has normal color vision. A formal color vision test, such as the Farnsworth test, should also be used. The color vision test should be repeated at appropriate intervals, such as every two years. The observer should be trained and experienced in observing color differences.
Before starting the tests, the test piece and the color master shall be brought into equilibrium at a temperature of 23 degrees plus/minus 2 degrees and a relative humidity of 50 percent plus/minus 5 percent. The decals shall be conditioned for at least 24 hours. For textiles, equilibrium is considered to be reached when the mass change determined after 24 hours of conditioning or at 2-hour intervals does not exceed 0,2 percent. For plastics, the conditioning period shall be specified in the relevant specification. Painted test panels shall be conditioned in accordance with STD 1021,1. If necessary, the test pieces shall be cleaned to remove all dirt. In the case of a bulk surface material, brush to even out the gloss.
During the evaluation, the light should fall on the test pieces mostly from above and should be distributed evenly over the evaluation area. The test pieces should be placed side by side, directly under the light source and as close together as possible. They should be observed at right angles to the evaluation area, at a distance of 0,5 - 1 m from the object. The angle of the test pieces should be varied between 0 and 110 degrees.
The evaluation shall be carried out under daylight illumination D65, incandescent light A and fluorescent light F11. When evaluating test pieces with an anisotropic appearance (e.g. metallic colors or textiles with a pile surface), the direction of the surface texture or the direction of application of the dye is important. The orientations of the test piece and the color master sample must be the same. In the critical evaluation, the test piece and the color standard are placed alternately with respect to each other.
If the color difference between the test piece and the main sample changes when the light source is changed, metamerism occurs in the test piece (metamerism is the appearance of a color in different colors and tones under different light sources).
If the setup allows, a black light can be used to detect any fluorescence. This should be checked when evaluating new colors. The observer should allow themselves a visual break when changing from one color to another, for example by looking at a neutral gray surface.
Among the numerous tests, measurements, analyses and evaluations that our organization has carried out for businesses in various sectors, it also provides testing services defined in the “Volvo STD 423-0041 Color Evaluation in the Light Booth” standard with its trained and expert staff and advanced technological equipment.
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