Glossary of terms

Technical terms simply explained

laser, light amplification by stimulated emission of radiation laser technical light source with special properties of the emitted rays: 1. monochromatic (extremely narrow-band wavelength range, to be limited exactly to 0.1 nanometers), 2. coherent (predictable route and interference properties through high constancy of the wavelength, important for example in distance measuring, holography); 3. parallel (ideal bundling capacity for high energy densities); thus numerous possible applications, including printing forme illustration, laser printing (photoconductive drum), marking plastic packages.

laser diodeLD diode laser semiconductor radiation source related to the LED, with emission ranges in the infrared, red, and violet ranges; applications include the illustration of printing plates.

LCD, liquid-crystal display écran à cristaux liquides see active matrix display

LCH, lightness–chroma–hue clarté – chroma – teinte see CIELAB

LED, light-emitting diode DEL, diode électroluminescente semiconductor light source which, depending on its design, can emit narrow to broadband wavelength ranges. Examples of applications: Imaging of photoconductive drums in digital printing systems, light source in spectral measuring devices as an alternative to the gas-filled light bulb, simulation of random illuminants in color-matching booths (patent: Just Normlicht), backlighting of LCD monitors and television sets.

light lumière wavelength range of the visible radiation of the electromagnetic spectrum, approx. 380 to 780 nanometers.

light fastness solidité à la lumière ageing stability of pigments and dyes vis-à-vis UV rays in natural daylight (simulated with xenon high-pressure lamps in accordance with ISO 12040, determined as fade resistance (résistance à la décoloration) of the Blue Wool Scale in accordance with DIN EN ISO 105-B01).

light gathering/trap captage de la lumière phenomenon in halftone printing in which incident light, in its reflection in the upper layers of the substrate, is prevented from leaving the substrate, because the printing ink layer of the halftone dot blocks the way; this occurs mainly in substrates with low opacity and increases the tonal value increase of the halftone print. The strength of the effect is also dependent on the screen ruling (screen resolution, l/cm or lpi) and the presence of a lacquer coating. For this reason, the light trap correction exponent (Yule/Nielsen) is handled empirically for the screenvalue formula of Murray-Davies; a light trap occurs in the formula as a divisor of the screen density and of the solid density in values between 1 (no light trap detectable) and 1.9.

light scattering dispersion de la lumière on rough/matt surfaces the effect of diffuse reflection, which causes a chaotic distribution of the radiated light. In the measurement of color and color density, only the share of scattered light is registered.

light source source lumineuse any self-luminant body

lighting conditions conditions d’éclairage technical conditions prevailing during a color stimulus; these include the illuminant of the source, the influence of the surroundings (neutral or colored, stray light) and the angle of observation (glare and reflection-free).

lightness, luminance clarté, luminance luminance L in candela per square meter [cd/m²], strength of a light perception. Each color sensation is also associated with a lightness sensation, i.e. the luminance channel light–dark supplements the two chrominance channels red–green and blue–yellow, e.g. L* in the CIELAB/CIELCH color space model.

line work , LW dessin au trait monochrome pixel graphics file with 1 bit color depth, i.e. binary status “hue” and “no hue”.

linearization linéarisation procedure in the calibration of digital printing systems and inkjet digital proof printers. Here, with the help of a spectrodensitometer, e.g. Techkon Spectro- Dens/SpectroJet, a control strip provided for the linearization, e.g. ECI Gray Control Strip, is recorded on a printed sheet in  order to be able to adapt the actual values to the target values. This option is also available on offset-print copies printedunder PSO/ISO-standardized conditions; there, the “GrayCon strips” are recorded for two purposes: 1. Quality monitoring of the printing press (with impakt medien iQIP and Techkon SpectroJet), 2. indirect RIP linearization through retroactive calculation of the print sheet measured values with respect to the imaging curve, which can then be corrected in the imagesetter RIP with a validation program, e.g. MMS/basICColor Calibri print control. So far it has been common practice to linearize the imagesetter RIP to a stepped wedge on the basis of a printing plate measurement, e.g. with the Techkon SpectroPlate image analyzer.

liquid-crystal color display écran à cristaux liquides see active matrix display

LMS color space espace LMC see fundamental stimulus

long color encre longue see ink stringing

long key/black noir long in the UCR-modified chromatic composition with gray component replacement GCR, the use of the achromatic process color black instead of the three chromatic colors CMY, in a wide section of the tone value range, that is, with a low starting point.

look-up table table de correspondance see CLUT

low-migration ink encre à faible migration classification of a printing ink when the permissible SML values (“specific migration limit”, in mg material per kg food) of all substances that have an adverse effect on the smell/taste/appearance of the packed substance (test substance: modified polyphenylene oxide, Tenax) fall below permissible limits (DIN EN 14338/1186-13).

lpi, lines per inch lignes par pouce see definition

lumen lumen see luminous flux

luminance luminance SI unit: candela per square meter [cd/m²]; non-SI units: Apostilb (asb), Blondel, Bril, Lambert (la), International Stilb (isb), Skot (sk), Stilb (sb); see also brightness

luminance factor facteur de luminance value A for marking the brightness of a surface color, independent of the color ordering system and thus comparable between systems; in CIEXYZ A is equated with the Y stimulus (green).

luminance factors facteurs de luminance standardized values for brightness signal formation in color television; the following applies for the 3 color channels RGB: “luma -red” = 0.299, “lumagreen” = 0.587 and “lumablue” = 0.114.

luminescence luminescence the ability of solids, liquids or gases to emit light of a certain wavelength spectrum during the transition from a stimulated state to a basic state. The emission of light always requires an internal or external stimulation: through electric current (LEDs, OLEDs), light particles (phosphorescence: afterglow; fluorescence: real-time luminescence), chemical reactions (luminol in forensic medicine, luciferin in glowworms), heat input (embers), X-rays (projection screen), amplification through stimulated emission (laser) etc.

luminescence scanner détecteur de luminescence detector for the presence of fluorescent pigments in printing inks and optical brighteners in paper, e.g. from Leuze, Sick.

luminescent colors couleurs luminescentes color stimuli of self-luminant bodies (lamps, monitors, data projectors); see also additive color blending; opposite: surface colors.

luminescent diode diode électroluminescente see LED

luminous efficiency function courbe d’efficacité lumineuse V(λ) describes the spectral luminous efficiency of the human eye in daylight for the 2° standard observer. The maximum in green is 555 nanometers. The luminous efficiency function also explains why human beings can distinguish more green color shades than red or blue, why “green” is good for the eyes and why green coats are usually worn in the operating theater.

luminous efficiency/yield efficacité lumineuse the minimum relationship between radiated and received luminous flux required for successful color measurement.

luminous energy quantité de lumière light energy times time in lumen seconds [lm·s]

luminous flux/power flux lumineux product of luminous intensity and radiated solid angle [candela times steradian, cd·sr]; the SI unit is lumen [lm]; the weakening of the luminous flux through absorption is measured as degree of remission and, as a spectral degree of remission, forms the basis for all colorimetric parameters over the entire visible wavelength range. With video projectors, the illuminance reaching a surface [lux times square meter, lx·m²] at a defined distance is designated “ANSI lumen” (IEC DIN EN 61947-1).

luminous intensity intensité lumineuse radiant power per solid angle [watt per steradian, W/sr] or luminous flux per solid angle [lumen per steradian, lm/sr], weighted with the luminous efficiency function V(λ); SI unit candela [cd]

LUT table de correspondance see CLUT

Luther’s demand condition de Luther demand to be met by the spectral characteristics of the overall system, formulated in 1927 by the color film pioneer Robert Luther, applied today to colorimetric measuring instruments/color densitometer. The components measured light source (spectral radiation characteristics), measuring filter (spectral transmission characteristics) and photorecipient (relative spectral sensitivity distribution) must match each other in such a way that when they interact, they allow the desired spectral evaluation, without the individual components having to meet certain requirements.