Why can't I find vex_distant light shader in the shop network? By pressing the TAB button, I can't find it. Here is the screen shot from a tutorial, what listed in the TAB menu are different from mine, why? Has it disappeared in houdini 12.5 apprentice. Thank you in advance!

It's still there but it is hidden.

In the Houdini textport you can use the “ophide” command to list all the hidden operators. v_distant is hidden as it is in the list.

You can do two things to add the operator to the scene.

1. You can unhide it then it will be available in the tab menu:

opunhide Shop v_distant

2. Using the textport, you can navigate to any shop network type and use the opadd command:

opcf /shop
opadd -n v_distant

This will add a distant light shop to your network.

Thanks for the help here, i wonder why some nodes are hidden? Are these nodes no longer used often in Houdini 12? is it because there are new nodes that introduced in the new version of Houdini that better replaced the old ones?

Yep.

They are kept around for backward compatibility for old scene files and I mean old, like 1998 hip files old for some of them.

understood, the follow up question is: the v-constant light shader is replaced by which node? thank you so much!

The reason is most likely tied to PBR as this light shader along with the other light shaders are most likely not supported by it.

The vex light shaders are still available as you now know by simply unhiding them as an option to use with Raytracing and Micropolygon rendering.

If you want these vex light shaders always available in Houdini, you can put these opunhide hscript commands in to a 456.cmd file that is always run when Houdini launches. It is best practice to create a net new text file called 456.cmd (make sure that windows doesn't put an invisible .txt extension there…) in to your $HOME/houdini/scripts directory then edit away. Houdini will look in to this directory (with Houdini at it's defaults) and load this file every time it opens or loads a new file.

You can use the $HFS/houdini/scripts/123.cmd file as a guide as to how to write the hscript lines in to the 456.cmd file in your home houdini scripts directory.