Page "learned" Paragraph 1355

A sufficiently good approximation for determining the end reflection losses R can be obtained from the angle independent Fresnel formula: Af.

For phosphor to fiber and fiber to air surfaces, and assuming Af, we obtain Af percent.

This value may be reduced to 4.6 percent by means of a ( very thin ) glass layer of index 1.5.

Hence, the Af factor for the output fiber coupler is Af.