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label-free: Describes microscopy techniques that do not require colorimetric or fluorescent labeling methods to visualize samples. For example, brightfield, phase contrast, and differential interference contrast (DIC) are all popular label-free techniques.; See also: brightfield, phase contrast, differential interference contrast, fluorescence
lamp: A light source that provides the illumination necessary to view specimens under a microscope, it usually refers to light sources utilizing bulbs, such as mercury arc lamps, halogen lamps, etc., and not lasers or light emitting diodes.; See also: light source, bulb, filament lamp, halogen lamp, mercury arc lamp, metal-halide arc lamp, xenon arc lamp, microscope lamp
large field-of-view (L-FOV): Many research microscope systems provide an 18 millimeter field of view, limited by internal lens diameters. Nikon offers a 25 millimeter field of view, and components or modules such as spinning disk units compatible with that size are specified as large field of view (L-FOV).; See also: field of view
laser: Light amplification by stimulated emission of radiation (LASER). Laser light is highly monochromatic, coherent, and intense. It has high directionality and can travel as a narrow beam. It is useful for applications such as confocal microscopy and targeted photostimulation.; See also: confocal microscopy, photostimulation, fluorescence lifetime imaging microscopy, light source
laser scanning microscope (LSM): A laser scanning microscope refers to a system where an image is built by scanning a laser illumination pattern across the sample (e.g., point-scanning, line-scanning) or the sample relative to a stationary laser illumination pattern.; See also: confocal microscopy, scanning microscope, confocal laser scanning microscopy, line-scanning confocal microscopy, point-scanning confocal microscopy, raster scanning
laser tweezers: see optical tweezers
lateral chromatic aberration: Aberration resulting from dispersion of different wavelengths by a lens. Different colors of light originating from a common point in the sample and removed from the optic axis will be focused at different points in the lateral (XY) directions in the image.; See also: aberration, axial chromatic aberration, chromatic aberration, dispersion, refractive index
lateral magnification: The ratio of image to object size in the directions orthogonal to the optical axis.; Synonyms: transverse magnification, areal magnification, XY magnification; See also: axial magnification, magnification
lateral resolution: The minimum distinguishable distance between features in an image. There are multiple criteria to define resolution such as Rayleigh, Abbe, and Sparrow. The Rayleigh criterion (.61*wavelength/numerical aperture) is most conservative, and describes the distance from the peak of a point spread function to its first minima.; Synonyms: XY resolution; See also: axial resolution, numerical aperture
law of refraction: see Snell's law
lens: An optical component made of glass designed to collect and project light to form magnified or reduced images of objects.; See also: perfect lens, ray optics, optical train, objective lens
levelling stage: A sample stage that can be adjusted via levelling screws such that the image of the sample appears flat and level.; See also: stage
light: Electromagnetic radiation with wavelengths in the visible range (~400-700 nm).; Synonyms: visible light; See also: electromagnetic spectrum
light diffuser: see diffuser
light emitting diode (LED): An electrical component that emits photons in response to current. Commonly used as a light source for microscopy due to being efficient, bright, and long-lived.; See also: light source, illuminator
light field microscopy (LFM): A single-snapshot volumetric imaging technique that uses a microlens array (MLA) to capture a set of 2D images of the object viewed from different angles. This angular information is used to reconstruct a 3D volume, at the cost of lower resolution compared to a conventional widefield microscope.
light meter: A tool used to measure the amount of light in a given location, commonly used in photography to determine optimal f-number and shutter speed.
light microscope: A microscope, usually with a catadioptric-based optical system primarily intended for observation of visible wavelengths of electromagnetic radiation. It is also common to utilize near-ultraviolet and near-infrared wavelengths in combination with a detector sensitive to those wavelengths.; Synonyms: optical microscope; See also: catadioptric, optical train, electromagnetic spectrum
light path: The path that light travels along through the microscope from the illuminator, to the object, and finally the observer or detector.; See also: optical train
light sheet fluorescence microscopy (LSFM): A technique in which a thin sheet of light is generated perpendicular to the optical path of the microscope to illuminate the sample, minimizing exposure outside of the focal plane and thus reducing photobleaching and phototoxicity. Can be scanned to observe large sample volumes quickly.; Synonyms: selective plane illumination microscopy, ultramicroscopy; See also: confocal theta microscopy, optical sectioning, multi-view fusion, water dipping objective, Bessel beam, Airy beam
light source: A source of light for use in an optical system such as a microscope. Common light sources include light emitting diodes, halogen lamps, lasers, and even the sun. It is the core component of an illuminator. It may also refer to the source in a ray tracing diagram.; Synonyms: source; See also: illuminator, light emitting diode, halogen lamp, laser, mercury arc lamp, metal-halide arc lamp, xenon arc lamp
line averaging: Similar to frame averaging, a line of pixels is scanned multiple times and the average intensity value at each pixel is kept, reducing Poisson noise.; See also: frame averaging, averaging, noise
line-scanning: see line-scanning confocal microscopy
line-scanning confocal microscopy: A technique in which laser light is manipulated to form a focused line across the sample in XY, which is then scanned unidirectionally to cover the field of view. Emitted light is projected to a camera, which integrates the signal to form an image of the full field of view.; Synonyms: line-scanning, slit-scanning; See also: point scanning confocal microscopy, laser scanning microscope, confocal microscopy
linear array sensor: A component in which multiple point-like detectors (pixels) are organized in a one-dimensional row.; See also: area detector
linear measurements: see micrometry
linear polarizer: see polarizer
linearly-polarized light: Light with an electric field amplitude that oscillates along one specific transverse angle.; Synonyms: plane-polarized light; See also: polarized light, polarized light microscopy, circularly polarized light, elliptically-polarized light
live cell imaging: A technique in which living cells are imaged to gain biological insight. There are a wide variety of strategies for maintaining cell health via stage-top or enclosure-type incubation. Live cell imaging is challenging because cells are often photosensitive and require reduced illumination intensities.; See also: heated stage
localization microscopy: see single molecule localization microscopy
locating flange: Surface along which two different microscope components fit together.; Synonyms: locating surface; See also: eyepiece flange, eyepiece-locating observation tube flange, objective-locating nosepiece flange, objective flange
locating flange of eyepiece: see eyepiece flange
locating flange of the objective: see objective flange
locating surface: see locating flange
long working distance objective (LWD): An objective designed with a long focal distance to enable deep imaging or to allow for more space around the sample.; See also: extra-long working distance objective, super-long working distance objective, working distance
longitudinal magnification: see axial magnification
longitudinal resolution: see axial resolution
longpass filter: An optical filter that blocks light with wavelengths shorter than some value and transmits light with wavelengths longer than that value.; See also: filter, shortpass filter, bandpass filter