LED butt coupling into lightguide

  • 30 December 2022
  • 1 reply

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Many LEDs are encapsulated in silicone. In regard to butt coupling light into a plastic light guide with similar index, my question: is it better to have a small air gap or not?

My most immediate issue with simulating this is that if I put the source (ideal Lambertian emitter) ‘Inside Of’ a silicone object, a larger fraction of the rays TIR inside… I’m guessing this needs a more sophisticated model, but I’m mostly looking for general advice. Any thoughts or guidance will be appreciated.


Best answer by Ethan 20 January 2023, 23:49

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Hi @John.Hygelund,

My first impression without further details is that you’d not want an air gap. TIR would be reduced if the index of the silicone object is in direct contact with the similar index plastic waveguide. You will get the most significant TIR with a silicone/air boundary. You’d also have two distinct boundaries for the rays to traverse before entering the waveguide.

Let me know if this suggestion helps.