BS ISO 26723:2020 Plastics — Determination of total luminous transmittance and reflectance.
5.1 The apparatus shall consist of a stabilized light source, an associated optical system, an integrating sphere with ports, and a photometer comprising a photo-detector, signal processor and display unit or recorder (see Figure 1).
5.2 The light source and the photometer shall be used in conjunction with a filter to provide an output corresponding to the photopic standard luminous efficiency V(A) (as defined in ISO/CIE 1 1664-1), which is identical to the colour-matching function j (A) specified in ISO/CIE 11664-1 under CIE standard illuminant D65 as specified in Iso 11664-2. The output of the photodetector shall be proportional to the incident flux, to within 1 % of the incident flux, over the range used. The spectral and photometric characteristics of the light source and photometer shall be kept constant during measurements.
5.3 The total port area (sum of area of the port a, b, c and d) shall not exceed 4,0 % of the internal
reflecting area of the sphere. It is desirable for the diameter of integrating sphere to he not less than
150 mm to he big enough for a specimen to pull together the scatter light to the thickness direction of the
5.4 Ports a, b and c shall he centred on the same great circle of the sphere. The angle between line ac and line bc shall be 14 O Where the line ac means the line which links the centre of port c to the centre of port a, and the line bc means the line which links the centre of port b to the centre of port C. Port d shall not be in the great circle on the sphere with port a, b and c.
5.5 The light source and its associated optical system shall produce a collimated light beam, no ray of which makes an angle of more than 0,05 rad (30) with the beam axis. The centre of light flux shall be matched up precisely with the centre of the port a. The cross-section of light flux shall be circular and have sharp image. The diameter of light flux at the port a shall be 0,5 to 0,6 times of specimen, excluding evaluation of reflectance for opaque specimen.
5.6 The white reference which is attached on the port c shall have the even high reflectance for all wavelengths of the visible ray. Barium sulfate and Polytetrafluoroethylene (PTFE) are suitable. The inner wall of the integrating sphere shall have a coating applied that has the same reflectance as a white reference.
5.7 The light trap which is attached on the port b or port c shall absorb light completely when port b or port c doesn’t have specimen nor white reference attached.
5.8 When the specimen has higher haze and higher thickness, specimen shape shall be circular and loaded with specimen holder specified on the Figure 3. The inner surface of specimen holder shall have metallic luster. Because the specimen holder can collect scattering light which go toward the edge of the specimen.BS ISO 26723 pdf download.