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Larger context for LACK in Corpus USbrown_UKbncw/US_brown.txt

These losses depend on fiber diameter and length, absorption coefficient, the mean value of the loss per internal reflection and last but not least, on the angular distribution of the incident light.
Explicit expressions (integral averages) are given in the literature.
Lacking reliable data for some of the variables, we are relying on experimental data of about 20 percent internal losses for 1 4-inch long, small (5-10 |m) diameter fibers.
This relatively high value is probably due to the small fiber diameters increasing the number of internal reflections.
Since we are considering here relatively small diameter (1-1.5 inches) fiber plates, their average thickness can be kept below 1 4 inch and their internal losses may be assumed as 15 percent (per plate).
The packing efficiency, F.R., of fiber plates did not receive much attention in the literature, probably as it is high for the larger fibers generally used, until rather recently.
For circular fibers in a closely packed hexagonal array, the packing efficiency is given by: **f where **f, and 0.906 is the ratio of the area of a circle to that of the circumscribed hexagon.
For the small diameter fibers now technically feasible and required for about 100 **f resolution, **f.