1.1.1 A two-field instrument must show two illuminated areas of equal size and shape,one filled with light transmitted by color standard, the other with light transmitted by the sample. These illuminated areas shall be disposed symmetrically about a vertical median line and shall be separated in a horizontal direction so that the horizontal separation of the closest portions subtends the eye of the observer not less than 2° nor more than 3.6°.
1.1.2 A three-field instrument shall show three illuminated areas in the field of view. Two are as shall be filled with light transmitted by two different color standards, and these shall be disposed symmetrically about the third area which shall be filled with light transmitted by the sample. The rectangular dimensions of each of the three areas shall be the same, and the left- and right-hand corners of the full field of view shall be rounded with radius not exceeding half the vertical dimension. The illuminated areas shall be separated in a horizontal direction by vertical lines so that the closest portion of the sample area and any one of the color standards illuminated areas subtends the eye of the observer not less than 0.3° nor more than 0.6°.
1.1.3 Each illuminated area in the two-field instrument shall cover a circle of diameter subtending at least 2.2°and may be enlarged to any size provided that no two illuminated points in the field of view are separated by a distance subtending more than 10°. In the case of the three-field direct viewing instrument, the subtending angles become 2.6° and 6.4°, respectively.
1.1.4 The angle subtended by a line of length d, in a plane perpendicular to the line of sight, and separated from the eye of the observer by a distance D, is given in degrees by 57.3 d/D. The angle subtended by the image of this line, seen by viewing it through an eyepiece of magnification M, is given in degrees by 57.3 Md/Di, where Di is the distance between the eye of the observer and the plane of the image.
1.2 Artificial Daylight Source - This may be a separate unit or an integral part of the colorimeter where the combined system of a source lamp (1.2.1), daylight filter glass (1.3), and flashed opal glass (1.2.2) are capable of producing spectral characteristics similar to northern daylight (that is, color temperature of 6700 more or less 300K) for use in the test.
NOTE
1.1 - When electric current is not available, the colorimeter may be designed to use diffused daylight provided that direct sunlight is avoided. Colored objects should be excluded from the immediate foreground when using diffused daylight.
1.2.1 Source Lamp - Consisting of a lamp of color temperature of approximately 2750K (or if a quartz halogen lamp is used, approximately 2900 K). A source lamp providing a translucent or opaque diffuse background of 900 6 100 lx brightness against which the color standards and samples are viewed has been found satisfactory to produce the necessary spectral characteristics. The source lamp shall be designed so that there is no extraneous light interfering with the observation.
1.2.2 Flashed Opal Glass - The background of illuminated opal glass shall be free from glare or shadows.
1.3 Filter - An acceptable daylight filter, which has been used in combination with the artificial daylight source and flashed opal glass to produce the spectral characteristics similar to northern daylight, is one where a spectrometric test indicates a transmittance of radiant energy of not less than 0.60 at 410 nm with a smooth curve down to a transmittance below 0.10 at 700nm without the pronounced bump that is characteristic of excess cobalt having an increased transmittance at 570 nm above a straight line drawn between the points indicating transmittance at 540 and 590nm, and also a transmittance band above 660nm. The transmittance of an acceptable filter shall not, at 570nm, exceed by more than 0.03 that indicated by a straight line drawn between the points indicating transmittance at 540 and 590 nm, nor shall the transmittance for 700 nm exceed that for any shorter wavelength (such as 660 nm) by more than 0.03.
1.3.1 An acceptable daylight filter shall also possess such characteristics that the chromaticity coordinates, x, y, and z, and luminous transmittance, T, when calculated from the spectral transmittance data using the 1931 CIE Standard Illuminant A, shall be as shown in Table 1.1.
1.4 Glass Color Standards - Use color standards as specified in Table 1.2. The standards shall be mounted in such a way that they may be conveniently manipulated. The width of the glass color standards shall not be less than 14mm.
1.5 Glass Container - The glass sample jar, Fig.1, is a true cylinder of clear colorless glass, having the following dimensions:
Internal diameter, mm 32.5 to 33.4
Wall thickness, mm 1.2 to 2.0
Total height, mm 120 to 130
1.6 Sample Cover - The sample cover can be made of any suitable material that is dull black on the inside and is designed to completely shield both containers as described in 9.1.