An air and light unit, also known as a breathing support unit, or mobile air unit is a specialized piece of firefighting apparatus used by first responders to provide supplemental lighting and self-contained breathing apparatus cylinders and cylinder filling services at the scene of an emergency.^[1] During prolonged incidents surrounding an immediately dangerous to life or health environment, first responders working in unsafe environments wear a self-contained breathing apparatus. The depleted air cylinders within the breathing apparatus will need to be replaced and refilled throughout the incident.^[2] The air and light unit has the ability to refill the cylinders while in the field using an onboard air compressor and cascade system.^[1] It also carries a supply of spare air cylinders. Air and light units are highly customizable and can vary greatly between departments.^[3] Units are also equipped with diesel generators which supply electricity to power portable lights and overall scene illumination equipment.^[4] This is usually done via a roof-mounted telescoping light bank. Units typically have the ability to supply electrical power in an emergency to a shelter, base camp, or medical facility.^{[citation needed]}

In the United States, Chapter 24 of National Fire Protection Association regulation 1901 outlines specifications for any air system mounted on firefighting apparatus.^[5]