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  > TOM'S LIGHTTRAP (TLT). By Tom
  > INTRODUCTION
 

A light trap is an invisible geometry in the space absorbing and terminating all the emission on its surface.
In behaviour, it can also be identified as an optical blackhole and it also has no indirect properties.

At first sight, the results seem similar to the ones could also be created by a hidden object.
However, in opposite to an ordinary hidden object, they don't reflect some amount of light back.

* An example showing a TLT dividing the lighting on the air:

 
  > WHAT MAKES A LIGHT TRAP
 
Basically any property giving an object zero reflectance is enough to make a light trap.

So there are 2 ways of making a LightTrap MXM:
1) A material having Nd=1 and Reflectance 0 = 0 (optionally blended with a ghost BSDF)
2) An emitter only material having zero emission (optionally blended with a ghost BSDF)
...and of course making the applied object "Hidden to Camera".

* An example showing a TLT object occupying space without generating indirect illumination.
 
  > BENEFITS OF TLT BODIES
 
TLT bodies gives you the chance to:

  • Make invisible geometries which holds and terminates the light.
    eg.You can put an invisible seperator in the middle of two lights and prevent their emission interact with each other.
  • Make invisible geometries which can weight the pass-through of light
    eg. You can place a mapped invisible light mask in front of an emitter without affecting the look of emitter shape itself.
  • Prevent illumination from emitters while keeping their visibility
    eg. You can enclose an emitter geometry inside a TLT body and prevent it emitting light while keeping the emitter visible in the scene.

    • * A TLT body covered spherical emitter is demonstrating the above example with glare applied on the right.

  • Casting shadows with invisible objects without having indirect illumination off from them.

    • * An example showing a weightmapped TLT plane casting shadows and meanwhile covering the light sphere shaping the illumination.

  • Making special effects...

    • * An example showing a TLT blocking the natural bounces of sky light in the room.

     
      > TLT IN ACTION
     
    Here are some animations showing TLT in action.

    		 
    		 
    First animation demonstrates a semi transparent TLT (weighted with a ghost BSDF) plane rippling in the space.
    Second animation demonstrates the same with texture mapped weights casting a fuzzy circular shadow.
    Third animation demonstrates a textured TLT body covering a spherical emitter causing uneven shadows around.
     
     
      > LIMITATION
     

    Currently, it's not possible to hide them from reflection and refraction.
    They will be reflected and refracted as black spaces.

    I hope you like TLT bodies and I'm sure it will end up better in your hands.

    Happy rendering,
    tom
     
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