Document ID: chunk:federal_register_of_legislation:F2024C00148:reg:1:p25
Version: federal_register_of_legislation:F2024C00148
Segment Type: reg
Provision Reference: reg 1 (pt 25/34)
Character Range: 203537–206748

is required. This reference standard should preferably be a flat mirror with a reflectance value as near as possible to that of the test samples.

              3.3. Flat mirror measurement

               The reflectance of flat mirror samples can be measured on instruments employing either the direct or the indirect calibration method. The reflectance value is read directly from the indicating meter.

              3.4. Non-flat (convex) mirror measurement

               Measurement of the reflectance of non-flat (convex) mirrors requires the use of instruments which incorporate an integrating sphere in the receiver unit (see Figure 2). If the instrument-indicating meter indicates ne divisions with a standard mirror of E per cent reflectance, then, with a mirror of unknown reflectance, nx divisions will correspond to a reflectance of X per cent, in accordance with the formula:

       Figure 1
       Generalised reflectometer showing experimental set-ups for the two calibration methods

       Figure 2
       Generalised reflectometer, incorporating an integrating sphere in the receiver

              4. Spectral tristimulus values for the CIE 1931 standard colormetric observer[14]

              This table is taken from CIE publication 50 (45) (1970)

       Explanatory figure
    Example of device for measuring the reflection factor of spherical mirrors

   C       =     Receiver
   D       =     Diaphragm
   E       =     Window of entry
   F       =     Window of measurement
   L       =     Lens
   M       =     Object window
   S       =     Light source
   (S)     =     Integrating sphere

Annex 7
Procedure for determining the radius of curvature "r" of the reflecting surface of a mirror
              1. Measurement

              1.1. Equipment

               A "spherometer" similar to the one described in Figure 1 of this annex having the indicated distances between the tracing pin of the dial gauge and the fixed legs of the bar is used.

              1.2. Measuring points

              1.2.1. The principal radii of curvature shall be measured at three points situated as close as possible to positions at one-third, one-half and two-thirds of the distance along the arc of the reflecting surface passing through the centre of this surface and parallel to segment b, or of the arc passing through the centre of the reflecting surface which is perpendicular to it if this arc is the longer.

              1.2.2. Where, owing to the size of the reflecting surface, it is impossible to obtain measurements in the directions defined in paragraph 2.1.1.5. of this Regulation, the Technical Services responsible for the tests may take measurements at the said point in two perpendicular directions as close as possible to those prescribed above.

              2. Calculation of the radius of curvature "r"

               "r" expressed in mm is calculated from the formula:

               Where:

               rp1 = the radius of curvature at the first measuring point,

               rp2 = the radius of curvature at the second measuring point,

               rp3 = the radius of curvature at the third measuring point.

Figure 1
Spherometer

Annex