Hi guys.

Trying to understand how LEDs project/form their beams. I took a macro photo of
a 10mm led and together with the datasheet, I deduced that the front of the LED
is a perfect sphere, and the LED emitting junction is just at the opposite end
of that sphere ('imaginary', as the body of the led is cylindrical there).
(eg. http://spie.org/x34513.xml)

First weirdness: with some math I seem to have deduced that, if the focal point
is indeed that spot, the IOR of the material should be 2.0 which is a very
exotic value for LED epoxies (from the docs I could find on the internet).

So I entered the above as a scene in povray, and have been suffering since :(

Questions: 

Can I put a light source inside the epoxy? Or do I have to make a small
bubble? 

I tried to enable photon mapping, but couldn't seem to get it working. Is
there some simple example - say a sphere + light + plane? Does this
work with the light inside an object?

The light seems to pass through the epoxy without refraction...

Enabling caustics, does give some lensing, but not realistically.

John

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> Hi guys.
>
> Trying to understand how LEDs project/form their beams. I took a macro photo of
> a 10mm led and together with the datasheet, I deduced that the front of the LED
> is a perfect sphere, and the LED emitting junction is just at the opposite end
> of that sphere ('imaginary', as the body of the led is cylindrical there).
> (eg. http://spie.org/x34513.xml)
>
> First weirdness: with some math I seem to have deduced that, if the focal point
> is indeed that spot, the IOR of the material should be 2.0 which is a very
> exotic value for LED epoxies (from the docs I could find on the internet).
>
> So I entered the above as a scene in povray, and have been suffering since :(
>
> Questions:
>
> Can I put a light source inside the epoxy? Or do I have to make a small
> bubble?
>
> I tried to enable photon mapping, but couldn't seem to get it working. Is
> there some simple example - say a sphere + light + plane? Does this
> work with the light inside an object?
>
> The light seems to pass through the epoxy without refraction...
>
> Enabling caustics, does give some lensing, but not realistically.
>
> John
>

There is nothing that prevent you from placing a light inside any 
object. If that object have any transparency, it will shine through.

It should be noted that the actual LED in the package shed light toward 
the BACK on a reflector. That reflector is not flat but dish shaped.
I've carefull examined some low power LEDs from the 70's. In those, the 
LED itself is maybe a little bit under 0.1 mm across.

If the light is inside the object, the object itself must have a photons 
block. That blok can be one of the followings:
photons{pass_through}
The photons just ignore the object on teir way to the intended target 
object.

OR
photons{target refraction on reflection on}
Makes the object interact with the photons. The photons shooting phase 
is MUCH longer (you shoot photons in every directions...) and you can 
have to deal with LOTS of photons.
If you have other lights and target objects in your scene, you may need 
to use target Spacing_Multiplier to get enough photons shoot at the LED 
case.



Alain

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