AATCC 148:2015 pdf download.Light Blocking Effect of Textiles and Related Materials: Photodetector Method
6.1 The measurement is of an SI-based quantity (lux), and the instrument should be calibrated to traceable standards at in- tervals recommended by the manufac- turer, typically on an annual basis.
7. Apparatus
7.1 The apparatus (see Fig. 1) consists of a rectilinear box constructed of light- impermeable materials with internal di- mensions of 360 ± 20 mm high, 280 ± 20 mm wide, and 200 ± 20 mm deep with matte black internal surfaces. On one side is a circular opening of dimensions to fit the sensor of a photometer with a clamp to hold the sensor in place at the internal surface of the box. Directly opposite is a circular opening 50 ± 3 mm in diameter. A sliding shutter of opaque material al- lows this opening to be completely blocked. Magnetic bars provide a conve- nient means of clamping a fabric speci- men in close contact with the outside wall of the opening, but other means of fixing a specimen against the opening may be used. A lamp housed within a metal re- flector is mounted so that it is aligned with the two holes in the box. The dis- tance from the lamp to the surface of the test fabric is 300 mm. To accommodate different lamps, it is convenient to have the housing mounted on a track so that the distance to the specimen can remain constant.
8. Test Specimens
8.1 For a (purportedly) evenly-block- ing material, cut or mark three represen- tative test specimens from the sample. Do not take specimens from within 10% of the width from the selvedge or machine edge of the fabric.
8.3 If testing reveals that the transmis- sion characteristics vary excessively be- tween specimens, even if not obvious to the eye, increase the number of speci- mens (see section 11 and 14.2).
8.4 Materials with small-scale (less than the 50 mm size of the specimen ex- posed) variation in transmission charac- teristics (based on fabric structure, or printed decoration, for example) may re- quire additional specimens to be cut.
8.5 Materials with large (greater than the 50 mm size of the specimens ex- posed) repeats of varying transmission characteristics may have the light block- ing effect of each area measured sepa- rately.AATCC 148 pdf download.