Wiktionary
light air
n. (context meteorology nautical English) A light wind with wind speed between 0,3 and 1,5 m/s; a Force 1 wind strength on the Beaufort scale.
WordNet
light air
n. wind moving 1-3 knots; 1 on the Beaufort scale
Usage examples of "light air".
Within a hundred yards of the ground it came to rest, floating gently in the light air, and at the same instant an alarm sounded at the sleeper's ear.
A two-master of a certainty, understandably if a bit aggressively flying a full complement of sails in the light air, but he couldn't tell anything more than that, not without his glass.