Try something like this in your ~/.bash_profile:

export PATH=$PATH:.:/usr/local/radiance/bin
export RAYPATH=.:/usr/local/radiance/lib

That export is needed to actually register the env var with the shell. Also make sure you have enabled these changes to your environment, by either trying the commands in a new shell window, or from the old one by typing source ~/.bash_profile, which will reload the thing in your current shell.