Light LPE labels cannot start with "m"

[Nevoreko]

Hey,

While deep diving in the LPEs in vray, I found this odd behavior, when I try to create a light select from a lpe label starting with "m" (ex. C.*<L.'mtest'>)I get this error:

[warning] V-Ray: Invalid light LPE label "mtest". Light LPE labels cannot start with "m"

As there is a proper error message, I take it that it's an expected behavior, but is there any reason to it? I'm joining a example scene where I compare it with Karma, that seems to have no problem handling it.

https://we.tl/t-6DGQXsMn2H

This is V-Ray 6.1.09 build 22528 in Houdini 19.5.605

Thanks,
Marvin

[viktor_angelov]

Hello Nevoreko

Could you share with us the whole Light Path Expression that you are using ?

[Nevoreko]

Hey viktor_angelov,
I did give the whole expression in my original message, it is also available in the hip file I provided

C.*<L.'mtest'>

[dian.nikolov]

Hey Nevoreko,

Labels starting with "m" are used to designate material labels. Since a light is not a material, the label is invalid.

Best regards,
Dian

[Nevoreko]

Alright thanks, no "myLight" labels for me then!

[Nevoreko]

I just found the part about this in the maya documentation, it's a bit confusing as the example used is literally "myLabel"... is there a way to go around it to have it work like in the example, or is it just hard-coded so that it can't start with a "m" and the example is misleading?
Or maybe it's something specific to maya and it has not the expected behavior in Solaris?

To use object labels, add V-Ray User Attributes to you object, where the attribute name is lpe_label and equals your custom label. For example, lpe_label=myLabel.

To use material labels, add Extra V-Ray Attributes > Light Path Expression Label to your material. When used in expressions, material labels require the m prefix.

See the examples below on how to set up object and material labels.

[dian.nikolov]

The documentation was misleading - object and light labels shouldn't start with "m". Should be fixed now, sorry for the confusion!

[Nevoreko]

Thank you!