[Raion]

So, whether you use .profile or your shell rc depends on your shell that you're using.

I use tcsh, and the same rules apply to csh. Generally .profile is pretty redundant to .cshrc for both. Just a line in your .cshrc near the bottom:

setenv LIGHTWAVE /usr/lightwave/Bin

would do it, but be warned. UNIX is CASE SENSITIVE unlike say, macOS or Windows. So Bin does not equal bin does not equal BIN does not equal bIN.

For KSH, you need to use .shrc IIRC or .profile. You'd use the export command for that, and the bash export command is moreorless ganked wholesale from the original bourne shell.