The gloss is one of the most important parameters of a surface, because it changes the perception of contours and shapes, affecting the overall viewing experience.
Brightness influence surfaces according to many factors like , angle of light incidence , position of the observer, physical characteristics of the surface and conditions of observation.
This parameter is important in many productive sectors and an efficient instrument is necessary to uniform the quality control . Gloss measurement has been unified according to international methods and standards like ASTM,DIN and ISO.
Basic physical principle for gloss measurement
When a light source radiates a surface undergoes a double effect : partly dispersed , partly reflected with opposite angle with equal amplitude opposite corner with respect to the initial radiation.
The brightness of a surface is calculated according to this specular reflection.
This last element determines the gloss level of a surface.
Specular reflection intensity is determined by the material and angle of incidence of the illuminating measured according to certain conditions.
Values are conventionally expressed in units of gloss ( GU : gloss units ) and refer to a scale based on the index of refraction of a black glass mirror with a reflection 100GU in relation to a specific angle. All non-metallic materials such as paints or plastics, can have a value associated to this data, while for highly reflective metal surfaces such as laminates and other crude materials, you can get up to 2000GU.
Types of Geometry - When and What to choose?
Gloss meters are divided in two types , mono - angular ( 60° ) and tri - angular ( 20° , 60° , 85° ).
Have more angular reference of the illuminant allows to improve measurement accuracy according to the level of gloss of the surface
• 20° measurements are more indicated for very bright surfaces ;
• 60° measurements are more indicated for medium bright surfaces ;
• 85° measurements allow to obtain optimized values for lackluster surfaces.
60° geometry is widely used due to its range of median use , however it’s recommended to refer to 20° value for measurements above the 70GU , while 85° is preferred with measurements under 10GU.
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