Add a note about the thin film redistributing energy between reflection and transmission and not violating energy conservation

Author: peterkutz

index.html

@@ -912,6 +912,8 @@
 
    - In the case of the metallic base the physics is somewhat ambiguous since, as described in the Metal section, the Fresnel factor for metal is defined according to the Schlick-based "F82-tint" parametrization, which does not specify the underlying physical complex IOR. We suggest here that some reasonable approximation is employed to map the Fresnel factor to the best matching effective complex IOR, for example that described by [#Gulbrandsen2014].
 
+   - Because the thin film is non-absorbing and interference-based, it only redistributes the probabilities of reflection and transmission; therefore, it should not violate energy conservation.
+
 ![Figure [ior_configs]: Schematic of all 8 possible IOR configurations, including those involving the thin-film.](images/IOR_configs.svg width="95%" align="center")
 
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