Lambertian Surface: A diffuse surface that reflects incoming light evenly in all directions, rather than ‘specularly’ (i.e.,in a single direction).
Laser: Acronym for Light Amplification by Stimulated Emission of Radiation, a laser is a device which produces a coherent (ie., all waves in phase), collimated (all waves moving in the same direction) stream of light.
Laser range finder: A device that uses a laser beam to determine the range to a target by bouncing a laser beam off the target, and measuring either the time of flight of the reflected beam, or the phase shift of the reflected beam (Doppler shift).
Level: Functionally similar to ‘brightness’ in a visual system, level sets the median thermal intensity in a given scene.
Level I, II, III Certification: Guidelines set by the American Society for Nondestructive Testing (ASNT) allow for professional certification of infrared thermographers. Level II certification is the highest technical rating, while Level III certification has to do with setting up preventative maintenance programs.
Liquid Nitrogen: Cryogenic (77 K) liquid used for cooling some detectors.
LOS: Acronym for ‘Line of Sight’, meaning that the observer (or imager) has a direct, unobstructed path to the target.
LWIR: Acronym for Long Wave Infrared, generally defined as the spectral range between about 7 to 14 microns. Most uncooled thermal imagers operate within this spectral range.
