Light-year Light-year The light-year is a unit of length used to express astronomical distances and measures about 9.46 trillion kilometres or 5.88 trillion miles. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word "year", the term light-year is sometimes misinterpreted as a unit of time. The light-year is most often used when expressing distances to stars and other distances on a galactic scale, especially in nonspecialist and popular science publications. The unit most commonly used in professional astrometry is the parsec
Light and air unit Light and air unit A light and air unit, also known as a breathing support unit, is a specialized piece of firefighting apparatus used by firefighters to provide supplemental lighting and SCBA air bottles at the scene of an emergency. During prolonged emergencies, particularly structure fires, where firefighters must remain on air (wearing their SCBAs), these air bottles will need to be replaced and refilled. The light and air unit has the ability to refill the SCBA bottles while in the field using onboard air compressors. It also carries a supply of spare air cylinders. These units are highly customizable