Relate in terms that people understand.  Context is important. 
As the quote obtained from a whatsapp group indicates, some words are useless or hard to conceive in different contexts. The idiom "light at the end of the tunnel" would not ring home or be fully understood by someone who has never been inside a tunnel.

While the comment about "we don't have light" is an exaggeration / made in jest, the humor is great emphasis.