Then wofully sich wightys
Shall gnawe thise gay knyghtys,
Thare lunges and thare lightys,
- Townley Plays, 1460
The word appears to be still around in knock your lights out.
Lungs were called lights because they were light. Both the words lung and light come from the Proto-Indo-European *legʷh- "having little weight". light is from a form with a *-t suffix, and lung from the nasalized form.
In Latin it became levāre "to lighten, raise", which combined with carne "meat" to form carnelevāmen, metathesized to Italian carnevale, literally "cessation of flesh-eating" (ODEE) - carnevale is the festival immediately preceding Lent.
light "brightness" is from PIE *leuk- and is cognate with lunar.