Determine clarity and ensure glossiness with a haze meter
There are two types of haze that affect a surface or material; Reflection haze affects how you see the light reflected from the surface of a material, while transmission haze affects how you see light passing through a material. In both cases haze appears as a kind of cloudiness that obscures the clarity and brilliance of a surface, or the ability to clearly observe the contents as in the case of clear films. A haze meter tests for and measures haze for a range of materials and surfaces. Testing for reflection haze in particular is an important part of coating quality control.
In this article we look at how the haze meter works, the standards related to the measurement of haze, and where to find haze meter suppliers in the US.
The two types of haze and how to measure them
Controlling both reflection haze and transmission haze is a vital part of ensuring a product or application that is of the highest quality and appearance. The standards and methods for detecting the haze types differ from one another.
1. Transmission haze – ASTM D1003
When light passes through a transparent material it interacts with the surface and the material and scatters. This diffusion can be caused by issues with the surface or by irregularities within the material itself – contaminants, air spaces, or poorly dispersed particles are all possible causes. Large irregularities cause narrow angle scattering, where light is scattered forward in a cone shape and there is a reduction in sharpness of vision through the material (measured as haze). Small irregularities cause wide angle scattering which causes the transmission to lose contrast (measured as clarity or see-through quality).
Under the ASTM D1003 transmission haze is measured through two test methods: Procedure A which uses a haze meter, and Procedure B which uses a spectrophotometer. Haze measured this way is done by observing the scattering of light while looking through the material – a light beam is passed through a sample, and the percentage of light which is diffused at greater than 2.5 degrees from the incident beam is defined as haze. The instruments use a spherical chamber to measure the light diffusion.
2. Reflection haze – ASTM E430
Reflection haze is a particular concern in the paint and coating industry, particularly for high gloss surfaces. A hazy, milky surface can reduce the apparent quality of a product. Reflection haze is a result of microstructures caused by poor dispersion, polishing,weathering, variations in the curing process, or even the coating application method. Reflection haze occurs when the surface diffuses low intensity light adjacent to the main direction of reflection – though the high level of reflection still makes the surface appear glossy and reflective, there is a milky haze on top of it.
Reflection haze is described as either narrow-angle reflection haze (bloom) and wide-angle reflection haze. Narrow-angle is light spread 2° from the specular, and wide-angle is spread 5°. Reflection haze is measured through the use of gloss and haze measurements – there are haze meter standards and gloss meter standards covered in the ASTM E430 over three test methods. The three test methods specify a different angle combination for the specular gloss measurement and narrow-angle reflection haze and wide-angle reflection haze measurements. The other haze meter standards are ASTM D4039 and ISO 13803.
Where to find haze meter suppliers in the US
Whether you need a haze meter for your business or for a project, there are companies across the US that supply haze meter products for the local market. These companies often have a wide range of coating measurement products available, so it is possible to purchase a consistent suite of instruments for ease of use. These companies include Elcometer, PCE Instruments, and Rhopoint. Many of these companies make haze meters that are inclusive of other testing measures, like gloss meters. Below is a small selection of the haze meters available in the US.
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|Company Name||Haze Meter Tool||Description|
|Elcometer||Elcometer 480||A gloss meter which includes a reflectance/haze measure. Available as single, dual and triple angle units.|
|Konica Minolta||CM-5 Spectrophotometer||A bench top measurement instrument with a range of capabilities, including haze readings.|
|Rhopoint||Novo-Gloss 20/60/85° Glossmeter||A gloss meter with haze meter capabilities to ASTM E430.|