Translucency, Port Size, and Area of View - an04_92r Follow

All diffusely reflecting objects scatter light internally, but in translucent objects the scattering points are far apart, allowing incident (source) light to travel a noticeable distance before it re-emerges. This can make a translucent object appear to glow when illuminated at one spot. Orange juice, milk, and many plastics are examples of such translucent materials.

Examples of translucent samples. Notice the 'glow.'

Normally, a translucent object is seen entirely illuminated, and the viewer tends to concentrate on a portion of the surface away from the edges in order to form a judgment of color. Therefore, if you wish to have an instrument assess color and to have it correlate well with visual observation, the open port area offered to the instrument should extend well beyond the area viewed, as shown below.

(illustrations)

Normally, a translucent object is seen entirely illuminated, and the viewer tends to concentrate on a portion of the surface away from the edges in order to form a judgment of color.  Therefore, if you wish to have an instrument assess color and to have it correlate well with visual observation, the open port area offered to the instrument should extend well beyond the area viewed, as shown below. 

(illustration)

An instrument with a larger port opening allows internally scattered light to be viewed by the sensor.
To illustrate, a translucent plastic plaque similar to the one shown at the very top of this Note was measured using two different instrument configurations. First, a LabScan XE was standardized with the 2-inch port plate installed and the matching 1.75-inch area view indicated to the software. Then, the LabScan XE was standardized with the 2-inch port plate installed and the smaller 1.00-inch area view indicated to the software. The sample was measured in each configuration, backed at the sample port with a white tile. Results are shown below.

(data table)

(See attached PDF file for the complete article with illustrations)

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