I posted this some time ago:
The LS460 seats are actually cooled by more than just recirculated air. They use thermoelectric-based cooling and heating similar to a solid-state cooler.
The following site used to list Lexus but the company has since been bought and no longer provides this detail. It used to have a diagram of the Lexus seat showing the thermoelectric plate.
Some posts claim that the AC needs to be on for the seats to cool to the max. It is also important to not have anything blocking the back of the seat at the bottom as that is where the heat is exhausted (and not a good place to put the ice cream on a grocery shopping trip).