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Photonics Dictionary: L

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LTS
laser thermal simulation; laser-triggered switch
luma
The luminance portion of a composite video signal, i.e., the portion of the signal that corresponds to the brightness of the image apart from any color value, giving a monochrome, or gray scale,...
lumen
A lumen is a unit of measurement used to quantify the amount of luminous flux, which is the perceived power of light. In other words, the lumen measures the total amount of visible light emitted by a...
lumen-second
SI unit of quantity of light.
lumia
A laser effect used especially for laser light shows. Lumia are created by placing a distorting medium such as rippled glass in the path of the laser beam.
luminaire
A complete unit containing a light source, globe, reflector, housing, socket and other necessary components for lighting.
luminance
Luminous flux emitted from a surface per unit solid angle per unit of area, projected onto a plane normal to the direction of propagation. Also known as brightness and luminous sterance.
luminance factor
Ratio of the luminance of a specimen to that of a perfect reflecting or transmitting diffuser identically illuminated.
luminance meter
A type of photometer calibrated in luminance units (candles per square unit, or lamberts). In photography an exposure meter contains a luminance meter to record the average luminance of a scene.
luminance range
An objective measure of an object's brightness that is derived from the ratio of the luminance of its lightest section to that of its darkest section.
luminescence
Luminescence is the emission of light that occurs without the involved substance undergoing a significant increase in temperature. In other words, it is the production and emission of light by a...
luminescent fiber
Fiber that emits luminescent radiation excited by ultraviolet, x-ray or high-energy particles.
luminescent greenhouse collector
A collector for photovoltaic power generation that consists of a thin plate that strongly absorbs sunlight striking its faces and luminesces efficiently. A large fraction of the luminescence is...
luminosity
Luminosity refers to the total amount of energy emitted by an astronomical object, typically measured per unit time. It quantifies the intrinsic brightness of the object and is often expressed in...
luminosity curve
Plot of spectral luminous efficiency vs. wavelength.
luminous
Pertaining to electromagnetic radiation as perceived by the eye; that is, with the contributions as wavelengths in the visible region weighted according to V(λ), which symbolizes the spectral...
luminous efficacy
Quotient of total luminous flux divided by total radiant flux; lumens per watt. (For a source, quotient of total luminous flux divided by lamp power input.)
luminous efficiency
Ratio of radiant flux weighted according to V(l), the spectral luminous efficiency, to the corresponding radiant flux.
luminous emittance
Luminous flux emitted per unit area of a source, expressed as lumens per area.
luminous energy
A measure of the time-integrated amount of flux. It has units of lumen-seconds and might be used to describe such things as the radiant energy that the eye would receive from a photographic flash.
luminous exitance
The total luminous flux given out per unit area; i.e., the sum of the luminous emittance and any radiation that is reflected from and/or transmitted through the surface: expressed as lumens per area.
luminous flux
Descriptive of the radiant power of visible light modified by the eye response. It is the measure of the flow of visible light energy past any given point in space in a given time period, and is...
luminous intensity
Luminous flux emitted by a source in a given range of directions; the unit of measure is the lumen/steradian, now known as the candela.
luminous paint
A mixture of phosphor with a trace of a radioactive element that emits faint light continually. It is used on watch dials and as a marker inside dark rooms to show the location of switches.
Lummer-Brodhun cube
A photometric instrument having two prisms clamped in optical contact to produce a photometric field with an acute dividing line.
Lummer-Gehrcke plate
A high-resolution spectroscopic device commonly used in the early 20th century as a component of double-beam interferometers. Light introduced at one end of the plane-parallel glass plate will be...
Luneburg lens
A dielectric sphere with an index of refraction that varies with distance from the sphere center. A parallel beam of rays is focused on the lens surface at a point diametrically opposite the...
LUPI
laser unequal path interferometer
LUT
look-up table
lux
SI unit of luminous incidence or illuminance, equal to 1 lumen per square meter.
lux-second
SI unit of light exposure.
luxmeter
An illuminometer designed to measure illumination in terms of luxes.
LV-ROM
laser vision read-only memory
LVDS
low-voltage differential signaling
LVDT
linear variable differential transformer
LVND
laser variable neutral density
LWIR
long-wavelength infrared
LWP
long-wave pass
lx
lux
Lyman continuum
A spectrum that is continuous in the UV region with borders ranging from the visible to 300 A and lower.
Lyman ghosts -> GHOST
global horizontal and sounding technique
Lyman-alpha radiation
The hydrogen-derived, ultraviolet radiation running from 1216 to 512 A, discovered by Theodore Lyman in 1914.
Lyot filter
A type of filter consisting of a series of birefringent crystals and polarizers invented by French astronomer Bernard Lyot for isolating and observing significant wavelengths of solar light.
Lyot stop
A physical stop that is conjugate to the entrance pupil and is used primarily to reduce diffraction effects at longer wavelengths.

Photonics DictionaryL

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