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To better understand how an LPE is constructed, the below tokens are used to define interactions. For most users, the pre-built LPE are easily selected and explained below.

LPE EventsDescriptionExample
<type event 'group'>
Scattering event specified by scattering type, scattering event, or lpe groupC<.[DS]'floor'>[LO] matches all light paths from the floor lpe group
Light, i.e. analytic and geometric lightsC[DS]*<L'key'> matches all light paths from the key light group
Emissive object, i.e. camera visible lights and material glowC[DS]*O matches all emissive object light paths
Match any relevant LPE event<.D> where the period represents R or T
Scattering Types  
ReflectionC<R[DS]>[DS]*[LO] matches all reflected light paths
Transmission or refractionC<T[DS]>[DS]*[LO] matches all transmitted light paths
Scattering Events  
Diffuse lobes (D1 to D4)CD[DS]*[LO] matches all diffuse light paths
Specular/Glossy lobes (S1 to S8)CS[DS]*[LO] matches all specular light paths
User lobes used to output material properties (U1 to U12)CU2L matches the camera visible user2 lobe, typically albedo
( )Parentheses allow grouping of a sequence of LPE eventsCDSL, C(DS)L, and CD(SL) are all functionally the same
|A vertical bar separates alternativesCD|(SD)L matches direct diffuse or specular-diffuse light paths
[ ]Square brackets will match any one of the enclosed LPE eventsC[D2D3]L matches direct diffuse2 or diffuse3 light paths
[^ ]
Match any one LPE event that is not contained within the bracketsC[^D2D3]L matches all light paths besides diffuse2 and diffuse3 (including specular and user)
Match preceding event zero or more timesC[DS]*[LO] includes all light paths (including emissive)
Match one or more timesC[DS]+[LO] includes all direct and indirect light paths, but not emissive
Match exactly n timesC<T[DS]>{2}[LO] includes all double transmission light paths
Match min or more timesC[DS]{2,}[LO] includes all indirect light paths
Match at least min, but not more than max times.C[DS]{4,4}[LO] gives the fourth bounce of light from the camera