PRODUCTS & PROCESSES
How to Measure Gloss
Consumers love gloss — this can be seen in almost every industry from automotive , to electronics , to baby toys . No matter the industry , gloss tends to be associated with luxury and wealth . Studies suggest that humans ’ innate love for glossiness could be based on the biological need for water : the glossier an object , the more likely to ‘ quench thirst ’.
From an industry standpoint , gloss can have a very specific purpose . By definition , gloss is an optical property that indicates how well a surface reflects light in a specular ( mirror-like ) direction — or , how lustrous or shiny an object appears . While many industries prefer a glossier finish , some require a more matte finish .
Why Measure Gloss ?
Gloss meters like the PosiTector GLS measure gloss after a product has been manufactured , improving the production process by identifying process issues , maximizing consistency , reducing waste , and improving overall quality . Surface texture , coating properties , and paint application can all have an effect on a coating ’ s appearance . While it ’ s easy for the human eye to detect large differences in gloss , like comparing a matte finish on a military asset to a glossy red sports car , smaller differences in gloss can be harder to see — but can still have a big impact on process control .
What is Reflectance ?
When light hits a surface , some of it is absorbed , and some is reflected . The reflected light is responsible for how the object is perceived . The nature of the reflection is generally related to the surface finish of the object . On a smooth , polished surface like a mirror , light is reflected opposite to the angle at which it arrives ; this is referred to as ‘ specular ’ reflection . On a rough surface , light is reflected at all angles and a relatively small amount of light reflects at the specular angle .
What is Percent (%) Reflectance ?
Reflectance is a measurement of the amount of light detected versus the amount of light sent and is expressed as a percentage . Gloss meters such as the PosiTector GLS can display both Gloss Units and percent reflectance .
What is the Gloss Value ? What are Gloss Units ?
Per ISO 2813 , the Gloss Value is a ratio of the reflectance of the test specimen to the reflectance of a standard polished black glass surface “ with a refractive index of 1,567 at a wavelength of 587.6 nm in the specular direction ”, multiplied by 100 . It is expressed in terms of Gloss Units .
What is Haze Index ?
Haze is the appearance of a “ milky ” halo or bloom perceived in reflective surfaces caused by microscopic imperfections in the surface ’ s texture . Haze Index is calculated and is defined by ASTM D4039 as the difference between gloss values measured at 60 ° and 20 °. The PosiTector GLS 20 / 60 and 20 / 60 / 85 are capable of calculating haze when selected within the Setup menu .
How is Gloss Measured ?
Digital gloss meters measure the surface using a calibrated light source and light sensor at opposite , specular angles to each other . Reflectance is determined by comparing the amount of light energy emitted by the source with the amount of energy received by the sensor . Gloss is then automatically calculated using a look-up table .
Gloss Meters include a reference standard built into the base of the unit . When turning the unit on or when selected from the menu , the instrument automatically calibrates itself using the known Gloss Unit values of the standard .
Choosing the Best Angle for Gloss Measurement
On most surfaces , as the viewing angle increases , the reflectance and Gloss Value also increase . This is often apparent to the naked eye : for example , on the case below there is little apparent reflectance when viewed from above , but when that same tile is viewed from a wider angle ( nearer to the surface ), visible reflectance can be seen . This phenomenon can be used to provide greater measurement resolution on high-gloss and matte finishes .
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70 MARCH 2022 read online : www . surfaceworld . com