In the third seat, it can be good tactics to open on a hand slightly below the usual strength for an opening bid. Such an opening is a ‘third-in-hand’ opener, and you may term it as semi- psychic.
One reason why it can be a good idea to open light is that if none of the first three players has a genuine opening then the fourth player probably has the best hand at the table and so is the favourite to become declarer.
By showing your suit, so long as it is a good suit, you should be helping partner with the opening lead.