LAMINAR AIR FLOW: Streamlined airflow in which the entire body of air within a designated space moves with uniform velocity in one direction along parallel flow lines.

LATENT HEAT: The heat required to change the state of a substance as in changing water to steam.

LEGIONNAIRES' DISEASE: An acute bacterial pneumonia caused by infection with Legionella pneumophila and characterized by an influenza-like illness followed within 1 week by high fever, chills, muscle aches, and headache. Symptoms may include dry cough, inflammation of the membrane covering the lungs (pleurisy), and sometimes diarrhea.

LOAD: The amount of heat per unit time imposed on a refrigerant system, or the required rate of heat removal.

LOUVER: An assembly of sloping vanes intended to permit air to pass through and to inhibit transfer of water droplets.

LOW LIMIT: The minimum desirable, or safe, temperature; the alarm given when the measured temperature drops below this selected temperature.

LUMEN: The flux on one square foot of a sphere, one foot in radius, with a light source of one candle at the center that radiates uniformly in all directions.