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Diffuse Reflection: lpe:C<RD>*[<L.>O]
Specular Reflection: lpe:C<RS>*[<L.>O]

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Diffuse Transmission: lpe:C<TD>*[<L.>O]
Specular Transmission: lpe:C<TS>*[<L.>O]

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A specular scene using iridescence and transmission (glass).

Now that we have some understanding of the main components, let's begin by looking at the parts used to organize an LPE

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+ means one or more events. This means after the initial event, begin collecting others. This means it will collect indirect lighting only as the first (direct) event is skipped. Below is only indirect diffuse reflection (the typical indirect light AOV)

lpe:C<RD>.+[<L.>O]

None

If none of the notations are used, it collects an event and then goes to the light, collecting only direct lighting. Below we omit the * and the +, only direct diffuse reflection is collected.

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The curly brackets can also take a range of values to render a set of bounces. Maybe you're only interested in collecting the effects of the 4th through 8th bounce? Or maybe you know where to begin or end but want the renderer to decide where that is.

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The Beauty Render

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Of course you can also ask for other data from a path to a light group like indirect diffuse reflection (usually known as indirect lighting) for later scaling in compositing.

lpe:C<RD>.+[<L.('key'|'fill')>O]

Now you can output whatever you need based on light groups!

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