The ratio of the speed of light in vacuum to the phase speed of light in a given medium. Absolute index of light refraction indicates the change in the speed of light while entering vacuum.
White, gray and black colors lacking color tones. Achromatic colors differ only by luminosity.
The color model wherein color reproduction is obtained by adding primary colors.
A method of color production using three primary colors.
Adjustment in optics – the process of identifying and removing errors of measuring instruments and adjusting the values to relevant technical requirements.
Adjustment is achieved by setting the correct interaction, mutual arrangement and relative movement of parts, components and systems of adjustable devices.
Lighting outside working hours.
The type of lighting generated by directional or diffused sunlight.
Lat.Amplitudo – magnitude
Amplitude – the maximum value of a periodically varying magnitude.
Angle of incidence in optics – the angle between the normal to the surface and the incident light beam.
The angle between the normal to the surface and the reflected light beam.
The angle between the normal to the surface and the refracted light beam.
A pair of mirrors positioned at a slight angle to one another.
Bimirrors allow shaping two coherent waves out of a single light source. The superposition of these waves produces an interference pattern that can be observed on the screen.
Bimirrors are an instrument used to empirically prove the wave nature of light.
A beam splitting occurring when passing through an optically anisotropic medium due to the dependence of the refractive index of light on its polarization.
The law that sets the dependence of Brewster’s angle on the refractive index of media:
If the tangent of the incidence angle at the interface between two dielectrics is equal to the relative refractive index, the reflected beam is completely polarized in the plane perpendicular to the plane of incidence.
Candela is a measuring unit for luminous intensity; the basic unit of the SI system.
CMYK color model – is a color model that describes the reproduction of any color by subtracting the four primary colors: cyan, magenta, yellow, and black.
A systematic set of color samples, which are used to determine the color by way of visual comparison with the color of the object measured.
The science of color measurement methods and quantification.
The influence of the light source spectral composition on the visual perception of colored objects, consciously or unconsciously compared with the perception of the same objects illuminated by a standard light source.
A measure of visual perception of colored items illuminated from experimental and standard light sources under certain conditions of observation.
The color parameter characterizing the purity of hues. The closer to the monochromatic color, the more saturated the color is.
There are several qualitative characteristics of color saturation:
- vivid saturation;
- strong saturation;
- deep saturation;
Unsaturated colors are characterized as dull, weak or washed.
Color model – a method of exact description of the process of producing colors by mixing several prime colors. The primary color models are as follows: RGB, CMYK, HSB and HLS.
The temperature of an absolutely black body, whereat it emits radiation with the same hue as the radiation under consideration.
Color temperature characterizes the spectral composition of light source radiation, as well as an intrinsic impression about the color of the light source.
The type of lighting that adds local lighting to general one.
A lens with the central part thinner than the edges, which allow the parallel beams striking the lens to radiate at the exit.
A device operating in an electrical circuit with various light sources and serving to stabilize the current at discharge.
An organized movement of a microscopic electrically charged body as a whole.
Convex lens – a lens with the central part thicker than the edges, which allow the parallel beams striking the lens to converge at the exit.
A lens with the central part thicker than the edges, which allow the parallel beams striking the lens to converge at the exit.
An optical device having a large number of openings separated by opaque intervals, whereat diffraction of light occurs.
Usually, diffraction grating looks like a set of multiple parallel strokes of equal width printed on a transparent or reflective surface at the same distance from each other. Diffraction grating is a key element of spectroscopic instruments.
An optical filter designed for the general or partial reduction of image sharpness and the muting of minor details.
Concave lens – a lens with the central part thinner than the edges, which allow the parallel beams striking the lens to radiate at the exit.
An organized movement of charged particles. The direction of the organized movement of charged particles is considered the direction of electrical current.
We differentiate between conduction and convection current.
A physical value equal to the ratio of the charge that has been transferred through the conductor’s cross-section over a given period of time to this time. Electric current intensity is measured in amperes.
A periodic or nearly periodic alternation of charge, current intensity, magnetic induction, voltage and other electrical and magnetic values.
Electromagnetic oscillations in ether, which are excited by charged particles, atoms, molecules, antennas and other radiating systems.
Electromagnetic radiation consists of elementary particles (photons) and extends in vacuum at the speed of light.
The lighting designed to evacuate people from premises when the regular lighting is off due to an emergency.
A section of optics, studying light propagation in optical fibers.
A gas discharge lamp wherein glow is reached by exciting the luminophor layer with ultraviolet radiation produced during discharge.
A lamp wherein luminescence is generated directly or indirectly from electrical discharge in a gaseous medium, metal vapor, or a gas-vapor mixture.
A section of optics that studies the laws of light propagation in transparent media, based on the concept of light rays.
The basic laws of geometrical optics are as follows:
- law of rectilinear propagation of light;
- law of independent light beams;
- law of light reflection;
- laws of light refraction.
Electric currents flowing in the ground used as conductive medium. Ground currents cause corrosion of earthed metal items, thus leading to their destruction.
An incandescent lamp made in the form of a quartz bulb filled with an inert gas with the addition of halogens or halogen compounds that provide the slow evaporation of the incandescent element. Halogen lamps are utilized in public spaces, motion-picture and TV producing studios, copiers and projection equipment.
The oscillations occurred where the value that causes deviations of any system from its steady state varies in sine or cosine fashion.
Harmonic oscillations are a special case of periodic oscillations.
Harmonic oscillations are a convenient abstraction that facilitates the study of oscillatory processes.
A lamp with sodium vapor whose partial pressure during operation totals some 105 Pa.
A method of determining wave amplitude and phase at a given point in space with an established amplitude and phase of a spontaneous wave front. According to Huygens-Freshel principle, each wavefront point is a source of secondary spherical waves that are coherent. The amplitude and phase of waves at each point in space is the result of the interference of secondary waves. Huygens-Freshel principle allows solving the simplest problems of light diffraction.
A method of determining the position of the wave front at the next sampling time based on its known current position. According to Huygens' principle, all the points passed through by the wave front at the current time, are sources of secondary spherical waves and
the position of the wave front at the next sampling time coincides with the surface bending around all the secondary waves. Huygens' principle allow explaining the laws of reflection and refraction of light.
The luminous flux incident on a surface unit. Illumination is measured in lux.
Surface illumination produced by a point source is directly proportional to the light intensity of the source and the cosine of the angle of incidence and inversely proportional to the squared distance from the source to the surface.
A lamp wherein light emission is reached by heating the filament (tungsten coil). Heating is carried out by passing an electric current through the coil.
A lamp which operates on the principle of high pressure mercury lamp, but lacking an electrode. The ionization of gas in the discharge tube is reached in the process of induction of a high-frequency electromagnetic field.
The optical radiation having a wavelength greater than visible light. Infrared radiation is subdivided into:
- short waves with the length of 800 to 1,400 nm;
- medium waves with the length of 1,400 to 3,000 nm;
- long waves with the length of 3,000 to 10,000 nm.
Generally, infrared radiation is measured in micrometers. Infrared radiation is emitted by all bodies having temperatures above absolute zero.
An electrical device that generates conditions necessary for discharge initiation.
The degree of luminance of the exteriors and interiors of buildings and constructions.
A gas discharge lamp wherein incandescence requires no electrode heating.
An electrical device for converting electrical energy into light.
An arc, mercury or fluorescent high pressure lamp used as an additional light source when forcing flowers in winter in the protected ground.
A lamp with a hot cathode, wherein incandescence is possible only with its electrode preheated.
The law of independent light beams – a postulate of geometric optics, stating that any propagation of light beams in a medium does not depend on whether there are other beams in the medium.
The law of light reflection – the law that sets the mutual arrangement of incident and reflected beams in case of specular reflection, as well as the position of the perpendicular erected to the interface between two media at the point of incidence:
1 – both beams are in the same plane;
2 – the incidence angle equals the reflection angle.
The law of rectilinear propagation of light – a postulate of geometric optics, stating that light travels rectilinearly in any homogeneous medium. The law of rectilinear propagation of light is a consequence of Fermat's principle.
The laws of geometrical optics, stating that:
1 – the incident ray, the refracted ray and the perpendicular erected at the point of incidence to the interface between two media, lie in the same plane;
2 – the ratio of the sine of the incidence angle to the sine of the refraction angle is a constant value for a given pair of media.
A phenomenon of dimming luminous intensity as light passes through a substance or as it is reflected from the surface.
Light absorption occurs due to the conversion of light wave energy into the internal energy of a substance or into the energy of secondary radiation having a different spectral composition and a different direction of propagation.
The alternation of photoreceptors’ threshold sensitivity to the existing light stimulus of constant intensity. In the course of light adaptation, absolute and differential thresholds are raised. Light adaptation is fully completed in 5 to 7 minutes.
A deviation of an optical beam propagating in a medium in all directions possible.
Light diffusion takes place due to the inhomogeneity of media and the interaction of light with particles of substances, whereat the direction of propagation and the frequency and plane of light wave oscillations are altered.
An integrated circuit that converts electrical current into light. Light-emitting diode is based on a semiconductor with a p-n junction wherein electromagnetic radiation with a narrow bandwidth occurs when electrical current passes through.
A device comprising elements necessary for fastening, connection and protection of lamps.
A device for measuring illumination.
The bending of light rays in a medium with a continuously varying refractive index.
An emitter of electromagnetic energy in the visible spectrum.
Light sources are divided into natural (sun, moon, etc.) and artificial (incandescent lamps, gas discharge lamps, etc.).
Light wave an electromagnetic wave in the visible spectrum of wavelengths.
An element of a luminaire made of transparent or opaque parts disposable so that the lamp be hidden from direct observation.
A lamp with sodium vapor whose pressure during operation does not exceed 104 Pa. This lamp produces pure yellow color; it is used for street lighting.
Lumen – in the SI system – the measuring unit of luminous flux. Lumen is the luminous flux emitted by a 1 cd point source of light in a solid angle of 1 cr.
Synonym: lighting fixture.
Lighting fixture – a device comprising a light source and fittings redistributing the luminous flux of the source in space.
A device designed to measure luminance
The radiation in the visible spectrum, as well as in ultraviolet and infrared bands, which:
- occurs due to the excess energy in the transition of a substance to its regular state after absorbing certain amount of energy;
- is supported by a set of atoms or molecules in a state close to equilibrium;
- differs from thermal equilibrium radiation;
- differs from diffusion in that some intermediate processes occur between absorption and emission, whose duration exceeds the period of a light wave.
Depending on the mode of excitation of substance, we distinguish radioluminescence, chemiluminescence, triboluminescence, photoluminescence and electroluminesce.
Duration of luminescence is divided into fluorescence and phosphorescence.
Lat.Lumen – light + Greek.Photos – carrying
Luminophor – a substance that emits light when exposed to electromagnetic radiation. Luminophors are used in fluorescent lamps, cathode-ray tubes and other devices.
Luminophor – a substance capable of luminescence.
Luminous efficiency is the ratio of the emitted luminous flux to the power consumed. The measuring unit of luminous efficiency is lumen per watt (lm/w).
The total amount of light passing through a surface per given time unit. The measuring unit of light flux is lumen.
The intensity of luminous flux per solid angle unit (steradian).
The curve showing the dependence of luminous intensity of a light fixture on the meridional and equatorial angles, obtained by the plane sectioning of the fixture’s photometric element. Indicates luminous flux distribution in space.
Lux – in the SI system – the measuring unit of illumination; the luminous intensity produced by a luminous flux of 1 lumen, uniformly and proportionally distributed over the surface area of 1 square meter
A gas discharge lamp that uses radiation of electric discharge in mercury vapor.
A gas discharge lamp wherein glow is produced by the radiation of a mixture of metal vapor and the decay products of thallium halides, indium or sodium.
A lamp comprising a bulb with both a discharge tube of a high-pressure mercury lamp and an incandescent coil, connected as a chain. The bulb may be covered with phosphor.
Sun- or moonlight emitted by or reflected from any source.
Natural light – in optics – a set of incoherent light waves with all possible directions of oscillations replacing each other quickly and randomly. The amplitude of natural light oscillations is (on average) the same along the entire range of directions.
A gas discharge light source with optical radiation occurring at arc discharge at low pressure in neon vapor. Neon lamp produces orange-red radiation and is used in signal, decorative and advertising lighting.
The ability of the eye to adjust itself to varying illumination.
The type of lighting supporting standardized lighting conditions (illumination and light quality) indoors and in places of production work outside of buildings.
Lat.Diffractus – broken
Optical diffraction – a deviation from the laws of geometrical optics, when light bends around small obstacles. Diffraction occurs when light propagates in a medium with pronounced irregularities.
A device that alternate the spectral composition and energy of incident light. Optical filter usually looks like glass admixed with certain salts and plastic films containing organic dyes. Subject to its chemical composition, optical filters permit light passage only through a certain band of frequencies of the incident radiation, absorbing the rest of frequencies.
An optical phenomenon that:
- occurs when combining two or more coherent light waves linearly polarized in the same plane;
- is a stable pattern of the resulting gain or attenuation of light oscillations at different points in space.
The orientation of the electric-field vectors and those of magnetic induction of light waves in a plane perpendicular to the light beam. Polarization usually occurs when light is being reflected and refracted, as well as at light propagation in an anisotropic medium. Optical polarization can be linear, circular and elliptical.
Electromagnetic radiation with a wavelength of 100 to 10,000 nm. Depending on wavelengths, optical radiation is divided into ultraviolet, visible and infrared.
A device that reflects luminous flux emitted from a light source to rearrange its spatial distribution.
The seven colors of the solar spectrum, which, while optically mixed, make up visible eye natural daylight: red, orange, yellow, green, blue, indigo, violet. Through multiple shades each primary color transits into the neighboring one.
A characteristic of luminous elements. Radiance is equal to the ratio of the light intensity emitted in the intended direction to the projected area of the luminous surface onto the surface perpendicular to the intended direction. Radiance is measured in cd/m2
Device that changes the direction and intensity of the flow of energy. Reflectors are made in the form of shield surfaces, enclosures, etc. Distinguished by the type of energy reflected are: optical, acoustic, thermal, electromagnetic reflectors and those used in nuclear technology.
A measure of the optical density of a medium equal to the ratio of light velocity in vacuum to light velocity in the medium.
Refractive index depends on light frequency and the parameters characterizing the state of the medium. We distinguish between absolute and relative refractive indices.
An automation element which, affected by mechanical, thermal, optical, and other physical inputs, abruptly changes physical quantities in a controlled circuit.
An additive color model that describes the reproduction of any color by combining the three primary colors: red, green and blue.
The evaluation criterion of the relative depth of illumination oscillations, calculated by the established formula
The reflection process that occurs as follows: the monochromatic radiation absorbed by the coloring agent of a coated surface is reflected from the surface to a lesser extent as compared to a white surface fully reflecting the entire incident light.
The sustained oscillations that exist in a physical system in the absence of external inputs. The amplitude and period of self-induced oscillations shall be determined by system properties. To maintain self-oscillation the system shall have an energy substrate.
A gas discharge light source wherein optical radiation occurs during arc discharge in sodium vapor.
A device wherein measurement and registration are carried out by way of spectral scanning and converting optical radiation into electrical signals by radiation detectors.
A physical method of quantitative and qualitative analysis of the composition and structure of substances, conducted by emission, absorption or reflection spectra.
Spectrum analysis is highly sensitive and is used in chemistry, astrophysics, metallurgy, geological prospecting, etc.
Lat.Projectus – thrown forward
Spotlight – a lighting fixture that focuses light in a limited spatial angle using an optical system of mirrors and/or lenses.
The ratio of the radiation emerging from the layer of material to the flow of incident radiation.
Tube diode an electrical vacuum device comprising a glass bulb hosting two electrodes, a heated cathode and an anode, and having unipolar conductivity.
If the anode is connected to the positive pole of the current source and the cathode – to the negative one, the thermions emitted from the cathode set their course for the anode, and current flows through the diode.
If the anode is connected to the negative pole of the current source and the cathode – to the positive one, the thermions emitted from the cathode return, and no current flows through the diode.
The speed of distributing an electric current impact on charges in a conductor. Fields with a velocity close to the speed of light carry arrange charged particles in an organized and relatively slow movement.
Electromagnetic radiation causing a visual sensation and occupying a spectral region from 380 to 780 nm. Visible radiation of different frequencies is perceived by human beings as different colors.
The process of adjusting visual perception, that consists in alternating absolute and selective sensitivity depending on luminous intensity.
Wave diffraction is a non-rectilinear propagation of light with accompanying interference phenomena.
A channel in a heterogeneous environment, along which directed electromagnetic radiation propagates. Shielded waveguides formed by specularly reflecting walls are a distinguished type of waveguides.
A surface for performing work or measuring and standardizing illumination.