Document ID: chunk:federal_register_of_legislation:F2024C00147:body:0:p62
Version: federal_register_of_legislation:F2024C00147
Segment Type: other
Provision Reference: 
Character Range: 204891–207757

A: 1/  Gas‑filled tungsten filament lamp operating at a correlated colour temperature of T68 = 2,855.6 K.

       1.3. CIE 1931 standard colorimetric observer: 1/  Receptor of radiation whose colorimetric characteristics correspond to the spectral tristimulus values ( λ), y( λ ), z (λ ) (see table).

       1.4. CIE spectral tristimulus values: 1/  Tristimulus values of the spectral components of an equi‑energy spectrum in the CIE (XYZ) system.

       1.5. Photopic vision: 1/  Vision by the normal eye when it is adapted to levels of luminance of at least several candelas per square metre.

       2. APPARATUS

       2.1. General

       2.1.1. The apparatus shall consist of a light source, a holder for the test sample, a receiver unit with a photodetector and an indicating meter (see figure 1), and a means of eliminating the effects of extraneous light.

       2.1.2. The receiver may incorporate a light‑integrating sphere to facilitate measuring the reflectance of non‑flat (convex) mirrors (see figure 2).

       2.2. Spectral characteristics of light source and receiver.

       2.2.1. The light source shall consist of a CIE standard source A and associated optics to provide a near‑collimated light beam.  A voltage stabilizer is recommended to maintain a fixed lamp voltage during instrument operation.

       2.2.2. The receiver shall have a photodetector with a spectral response proportional to the photopic luminosity function of the CIE (1931) standard colorimetric observer (see table).  Any other combination of illuminant‑filter‑receptor giving the overall equivalent of CIE standard illuminant A and photopic vision may be used.  When an integrating sphere is used in the receiver, the interior surface of the sphere shall be coated with a matt (diffusive) spectrally non‑selective white coating.

       2.3. Geometric conditions

       2.3.1. The angle of the incident beam (Ɵ) should preferably be 0.44 ±0.09 rad (25 ± 5º) from the perpendicular to the test surface and shall not exceed the upper limit of the tolerance (i.e. 0.53 rad or 30º).  The axis of the receptor shall make an angle (Ɵ) with this perpendicular equal to that of the incident beam (see figure 1).  The incident beam upon arrival at the test surface shall have a diameter of not less than 19 mm.  The reflected beam shall not be wider than the sensitive area of the photodetector, shall not cover less than 50% of such area, and as nearly as possible shall cover the same area segment as used during instrument calibration.

       2.3.2. When an integrating sphere is used in the receiver section, the sphere shall have a minimum diameter of 127 mm.  The sample and incident beam apertures in the sphere wall shall be of such a size as to admit the entire incident and reflected light beams.  The photodetector shall be located so as not to receive direct