The specimen is illuminated with a white light LED at a15° angle and the lightness is detected under three viewing angles to simulate visual evaluation under different observing conditions: 15°, 45° and 60° measured from the specular reflection.
The mottling meter is rolled across the surface for a defined distance of 10 to 100 cm and measures the lightness variations point by point.
The measurement signal is divided via mathematical filter functions into 6 different size ranges and a rating value is calculated for each angle and mottle size. The higher the v value is, the more visible the mottling effect. The measured values are displayed in a graph showing the mottle size on the X-axis and the rating value on the Y-axis. Thus, target values for small and large mottle sizes can be established for paint batch approval as well as process control.