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Reflection Haze and Compensation


Reflection Haze

Reflection haze is an optical phenomenon usually associated with high gloss surfaces, it is a common surface fault that reduces appearance quality. It is characterised by a surface in which reflections are visibly shallower with a milky finish, in addition halos are often visible around reflections of strong light sources.

The difference between low and high haze: The image on the left has low haze and has a deep reflection whereas the image on the right has a much shallower finish.

 

A high gloss finish with haze exhibits a milky finish with low reflective contrast- reflected highlights and lowlights are less pronounced.

On surfaces with haze, halos are visible around the reflections of strong light sources.

 

Causes of Reflection Haze

Haze can be described as as near specular reflection, it is caused by a microscopic surface structure which slightly changes the direction of a reflected light causesing a bloom adjacent to the specular (gloss) angle. This causes the surface to have reduced reflective contrast and a shallow milky surface to be visible in the reflection. In the coatings industry, this microscopic surface texture is often due to poorly dispersed raw materials, incompatible raw materials or oxidisation and weathering.

For polished metal surfaces haze is often associated with polishing marks or chemical residue.

 

Gloss & Haze Measurement with IQ Array Technology

The Rhopoint IQ uses a 512 element linear diode array which profiles reflected light in a large arc from 14 to 27°. The IQ instrument processes this high resolution data, selecting individual elements within the array that equate to the angular tolerences outlined in international measurement standards.

In a single 20° measurement, the following calculations are made by:

 

Auto Adjustment on Curved Surfaces

A major advantage of the IQ is that it automatically compensates for curved or textured sample surfaces by virtually adjusting the measurement position. Conventional gloss-hazemeters have fixed optics which can make measurement unreliable as any sample curvature will reflect light away from the centre of the measurement sensor causing errors.

The IQ automatically adjusts sensor position by sensing the peak of the reflected light, the laws of reflection state that the incident angle is equal to the reflection angle thus the peak equates exactly to the 20° gloss angle.

The IQ automatically adjusts for non-flat surfaces by sensing the reflected peak and virtually adjusting the position of the sensor.

 

Diffuse corrected haze measurement with IQ array technology. 

Reflection haze is caused by micro texture on a surface which causes a small amount of light to be reflected adjacent to the gloss angle. For white surfaces, bright colours and metallics, a certain amount of diffuse light, reflected from within the material, is also present in this region. This diffuse light exaggerates the haze signal for these surfaces causing higher than expected readings.

The Rhopoint IQ compensates for reflection from within the coating for highly reflective pigments, metallic coatings and speciality pigments, allowing the haze of any painted surface to be measured.

 

Corrected haze measurement on metallic coatings

For non metallic surfaces, the diffuse component is lambertian- it is equal in amplitude at all angles in relation to the sample surface. Conventional gloss-hazemeters measure diffuse reflection using a luminosity sensor positioned away from the gloss angle. Luminosity is subtracted from the haze signal allowing non metallic surfaces measured independent of their colour.

An advantage of the Rhopoint IQ is that unlike a conventional instrument, compensation is calculated using a region adjacent to the haze angle. This techniques gives compatible readings on solid colours but also compensates for diretional reflection from metallic coatings and speciality pigments.

The Rhopoint IQ goniophotometric captures compensation information from a region adjacent to the haze measurement angle, this means it can be used on metallic coatings which reflect light directionally.

 

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