Difference between Frensel reflection and Total Internal Reflection

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SUMMARY

The discussion clarifies the differences between Fresnel reflection and total internal reflection in the context of LED efficiency. Fresnel reflection occurs at a single interface due to impedance and refractive index discontinuities, while total internal reflection involves two interfaces that are optimally spaced to enhance light reflection. Both phenomena can occur at the semiconductor/air interface, as well as at the epoxy/plastic and air interface. Understanding these concepts is crucial for optimizing light extraction in LED designs.

PREREQUISITES
  • Understanding of optical physics, specifically light behavior at interfaces.
  • Familiarity with refractive index and impedance concepts.
  • Knowledge of LED technology and light extraction methods.
  • Basic principles of lens design and light propagation.
NEXT STEPS
  • Research "Fresnel equations" to understand the mathematical basis of Fresnel reflection.
  • Explore "total internal reflection" and its applications in optical fibers.
  • Investigate "LED light extraction techniques" to improve efficiency.
  • Learn about "lens design for LEDs" to optimize light output.
USEFUL FOR

Optical engineers, LED designers, and anyone involved in improving the efficiency of light sources will benefit from this discussion.

hairbair
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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.
 
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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
 


hairbair said:
Do they both occur at the semiconductor/ air interface?
There's a interface between epoxy/plastic and air.

ledsfigure4.jpg


These lenses are designed to get the light out. :biggrin:

ledsfigure5.jpg


But they can't get it all out.

ledsfigure6.jpg



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

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