D/8°and 45°/0°are two kinds of illumination geometry with different optical geometry design. D/8°illumination geometry is more widely used for the color comparison and measurement of high-gloss materials; 45°/0°illumination geometry is mainly used in printing and packaging industries. 

For a proper color evaluation, ensure cleanliness, use standardized observation conditions, eliminate stray light, and periodically change the lamps.

Powder paint gloss levels are commonly classified as:

● Flat/Matte: 0–10 GU

● Satin: 10–40 GU

● Semi-Gloss: 40–70 GU

● Gloss: 70–85 GU

High Gloss: 85+ GU
These ranges can vary by manufacturer and application angle.

The various colors can be measured by the way a surface reflects, absorbs, or transmits light at different wavelengths. These responses may be measured using instruments such as colorimeters or spectrophotometers to give numeric values in a standardized color space such as L *a*b*.

A colorimeter is used to measure the intensity of color of a solution by measuring its absorbance at selected wavelengths of light. It is widely applied in chemistry, food, pharmaceuticals, and quality control to determine concentration, track color changes, or product uniformity.

L*a*b* is an L*a*b* color space. The L* is a measure of lightness (as 0 = black, 100 = white), a* indicates the green to red axis, and b* indicates the blue to yellow axis. It is also common in color measurement in terms of precision and reliability.

Standard light sources make sure that the results of color evaluations are comparable and consistent, no matter when and where the assessments are made, or the varying production runs.

Coating thickness is best measured with a coating thickness gauge specific for the type of substrate. Magnetic and eddy gauges are best for metals while ultrasonic gauges are best for non-metals. These devices provide measurement accuracy and consistency. 

Spectrophotometers can only measure haze if it has haze measuring capabilities, as many measure color and transmittance.

Look for dirty or fingerprinted glass along the optical path, recalibrate with standards, and check the set-up for outside light so that it is controlled. If the problems still exist, please reach out to the helpdesk or book a service with your professional service.