The difference between gloss and brightness is that gloss is (uncountable) a surface shine or luster/lustre, while brightness is the quality of being bright.
The glossmeter performs measurement on flat surfaces and operate like a refractometer.
Gloss and brightness of a particular surface is measured in “Gloss” and it is an optical property, based on the relationship between light and the physical characteristics of the surface, which means the surface capacity to reflect light in a specular way.
Gloss importance
Brightness is one of the most important parameters of a surface, because it can alter the perception of profiles and shapes, influencing the visual experience.
Brightness acts on the surfaces according to different aspects: angle of incidence of light, observer position, physical properties of surface and observation conditions.
This parameter plays a key role in several production sectors where metrological instruments are relevant in order to standardise the quality control.
Brightness measurement was consolidated according to international methods approved by ASTM, DIN e 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 but with equal amplitude, 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.
Measurement scale
Values are conventionally expressed in units of gloss (GU : gloss units) and they 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, the user can measure get up to 2000GU.
Geometry Types – When and Which one to Choose?
Gloss meters are divided into two types, mono-angle (60°) and tri – angle (20°/60°/85°).
To have more angular references of the illuminant allows improving measurement accuracy according to the level of brightness of the surface.
• Measurements at 20° are more indicated for very bright surfaces;
• Measurements at 60° are more indicated for medium bright surfaces;
• Measurements at 85° allow to obtain optimized values for little bright surfaces.
60° geometry is widely used thanks to its range of median use, however it is recommended to refer to 20° value for measurements above the 70GU, while 85° is preferred for measurements under 10GU.
Example: Measurement of the specular brightness of a painting film
The moment we are going to paint a wall, we need to decide even about the finish: matt, satin or glossy?
Colour can change according to the brightness grade.
EN ISO 2813 provides for the use of the gloss meter to measure the mirror brightness of a painting film.
Caparol Media, the web portal for colour, decoration, isolation and restoration, shows us in 5 steps how to make measurements.
1. Prepare the sample to be measured by applying a paint film and let it dry at 23°C and with 50 % UR;
2. Wait 16 hours for conditioning at constant temperature and RH rate;
3. Calibrate the gloss meter
4. Repeat the measurement six times in different positions, in a parallel and perpendicular direction to the drafting of the film;
5. Calculate the average of measured values and identify the reference ranges.
Upon request, we can carry out calibration report on the whole instrument or on the different angles (20°-60°-85°).
Which are the 5 strength points of the 3 angles digital glossmeter by Sama Tools?
- Attractive design
- Compact size
- Three-angle geometry of the lamp
- High-precision
- Ideal for quality control on production line or in the field
Thanks to the master supplied with the instrument, calibration could be performed in few seconds.
The 3 detection geometries, respectively 20°, 60° and 85° allow maximum flexibility of use, covering low, medium and high brightness surfaces.
Glossmeter applications:
– Brightness measurement of ink, paints, sealing wax prints.
– Cladding and processed wood products
– Decorative building materials: marble, granite, glass, glass blocks, etc.
– Plastics or papers
Who was the inventor of the glossmeter?
According to Wikipedia, the first one who realize an instrument for brightness measurement (of paper) was Ingersoill in 1914.
The “Glarimeter” (as it was initially called), was based on the principle that light was polarized in a specular way.
The light was incident at an angle of 57.5 ° and employed a contrast method to subtract the specular component from the reflected light with a polarizing element.
