Difference between Frensel reflection and Total Internal Reflection

[hairbair]

What exactly is the difference between Frensel reflection and total internal reflection with regards to the efficiency of an LED? Do they both occur at the semiconductor/ air interface? I am a bit confused, thanks for the help.

 

[jsgruszynski]

Not difference - they are related.

* Fresnel reflection: one interface reflected like a transmission line due to impedance/refractive index discontinuity

* Total internal reflection: two interfaces spaced just at the right distance to constructively reflect or cancel, where each interface has Fresnel reflection

 

[dlgoff]

Do they both occur at the semiconductor/ air interface?

There's a interface between epoxy/plastic and air.

These lenses are designed to get the light out.

But they can't get it all out.

Thanks to http://zeiss-campus.magnet.fsu.edu/articles/lightsources/leds.html for the images.