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Sunday, August 11, 2013

The Physics of Light

It is important before measuring different optical properties of paper to understand the interaction of light  with paper and how this interaction affects what we see.



The image above illustrates the behavior of light striking paper. When a ray of light strikes a sheet of paper, four possible results can occur, namely: reflection, transmission, scattering and absorption.  

REFLECTION - Surface (specular gloss) reflection occurs where the angle of viewing equals the angle of incidence. 

TRANSMISSION - Light passes through the sheet and is lost, thereby reducing brightness.

SCATTERING - Light rays undergo multiple reflection and refraction from fibers causing an increase in brightness.

ABSORPTION - Light strikes colored matter and is absorbed and converted to heat thereby reducing brightness.

 A future post will discuss in more detail the aspects of scattering; refraction and (non-specular) reflection.