ISO Brightness, Illuminant D65, UV Adjusted and Excluded

This test is performed to determine the defuse reflectance factor of paper, solid board or folding board. A test piece is illuminated diffusely in a standard instrument and the light reflected normal to the surface is either allowed to pass through a defined glass filter and then measured by a photocell or measured by an array of diodes, where each diode responds to a different effective wavelength. The brightness is then determined directly from the output from the photocell, or by calculation from the diode outputs using the appropriate weighting functions.

Operate the instrument in accordance with ISO 2470-2 and the manufacturer’s instructions.

Leave the samples exposed for 24 h to 23°C and 50% R.H., according to ISO 187.

Calibrate the instrument according to the instrument maker’s instructions, using a non-fluorescent ISO reference standard of level 3 (IR3). Adjust the UV-content to the C/2° Illuminant/observer.

Each sample pack is made of a pad of paper to be tested and a coloured cover sheet.

Remove the coloured protective sheet from the test piece pad.

Place the test piece in the position indicated on the cover sheet.

Without touching the test area, use the procedure appropriate to the instrument to measure the intrinsic blue reflectance factor of the top side of the test piece pad without and with the UV (C) 420 cut-off filter. Read and record the measures. Move the measured test piece to the bottom of the pad and determine the intrinsic blue reflectance factor for the next and similarly for the following test pieces, until at least ten test pieces have been measured.

Report 10 measures of the intrinsic reflectance factor, as the diffuse blue reflectance factor (ISO brightness), their mean and standard deviation calculated to 3 significant figures.