A

Absorption: conversion of radiant energy into a different form of energy caused by the interaction of matter.

Absorption factor: ratio between the radiant or luminous flux and the cutting light flux in specific conditions.

Adjustment: the process by which the status of the visual system changes according to the luminances or the coloured stimuli it perceives.

Adjustment (eye): focal adjustment of the eye, generally spontaneous, aimed at obtaining the maximum visual acuity at varied distances.

Ambient light: lighting in which the light on the working plane or on an object does not originate from any particular direction.

Analogue(al): In electronics, the system of physical quantities that vary with continuity thanks to the action of an operator or of a control system.

Alternator – Machine that transforms mechanic energy in alternating current electricity.

Arc discharge (in a gas or vapour): electric discharge characterized by a cathode fall. Apparent colour: Common expression used to describe the impression of colour when we look at a light source.

Average illuminance (E?): in relation to a surface. Illuminance average value in relation to a specific surface.
Cylindrical, semicylindrical, semispherical, spherical average illuminance:(see chapter 1.1).

Axis of the beam: the direction passing through the middle of the solid angle delimited by directions that have a light intensity equal to 90% of the maximum intensity of a device.

B

Ballast – Units connected to discharge lamps (often kept separate from projectors), which contain inductors and other starting devices to obtain the necessary circuit conditions (voltage, current and sinusoid). The inductor serves initially to develop a high potential to effect the discharge and then to limit the flux of current when the lamp is switched on. Electronic ballasts eliminate the “flicker” effect of lamps.

Beam aperture: the angle (on the plane containing the axis of the beam) beyond which light intensity falls below a percentage predetermined against its maximum intensity.

Beam efficiency: ratio between the flux emitted inside the solid angle created by the beam aperture and the flux of the naked lamp.

Blackbody (Plancks radiator): thermal radiator that completely absorbs all the cutting radiation, of any wavelength, from any cutting or bias direction. This radiator presents, with any wavelength, the maximum spectrum density of emissivity at any given temperature. The spectrum density of blackbody emissivity depends only on its temperature and is described by Plancks Law.

Blackbody locus (Planckian locus): the line on a chromatic diagram representing a blackbody chromaticity at different temperatures.

Bladed screen: screen whose shielding elements are blades made of opaque or translucent material.

Brilliancy: attribute of a visual sensation according to which a surface seems to emit more or less light.

Built-in luminaire: luminaire istalled on the ceiling, on a wall or other surfaces, so that its visible part is limited to the emission surface and if necessary to the source and the optical system.

C

Catenary configuration: configuration of street lighting devices that are suspended so as to the axis of the projector forms a right angle with the street axis.

Chromaticity: attribute of the colour of a stimulus, it can be identified either through chromatic coordinates or through its main or complementary wavelength, and its purity.

Chromaticity diagram: bidimensional diagram that shows the result of color mixings whose chromaticity can be univocally represented by an individual point of the diagram.

CIE photometric reference observer: ideal observer whose spectrum sensitivity curve corresponds to the V(?) function for photopic vision or to the V(?) for scotopic vision, and that is consistent with the additive law implied in the definition of light flux.

Cold cathode lamp: discharge lamp designed to switch on without the pre-heating of the electrodes.

Colour – Visual sensation given by the stimuli that reflected light offers to the eye. The human eye perceives the colours comprised between red (low limit of the range) and violet (high limit): below the range we have infrared rays and above it ultraviolet rays. They are not visible but it is possible to perceive the energy that is transported by the light when it hits the epidermis. Light in physics is considered in its ondulatory component (as an electromagnetic wave). The two limits (red and violet) thus correspond to the wavelengths at the limit of the visible.

Color efficiency: effect of a lighting device on the chromatic aspect of illuminated objects, aspect which is consciously or unconsciously compared to that of the same objects illuminated by a reference lighting device.

Colour efficiency index (Rp): quantitative assessment of the degree of compatibility between the psycho-physical colour of an object illuminated by the test lighting fixture and that of the object itself illuminated by the lighting fixture of reference, having taken into consideration the status of chromatic adaptation.

Color scale: plane scale in which the points, defined by their respective three-color coordinates, represent the chromaticity of color stimuli.

Colour space: Geometrical representation of colours in space. It is generally tridimensional.

Colour temperature – Physical parameter that indicates the temperature of the light beam. In general it is considered in reference to white (in physics it represents the sum of all available frequencies), its value is indicated in K° (i.e. absolute temperature: 0°=-273,15°K). The colour temperature of the sun light is about 6,200°K and is continuous, that is the intensity at the source always remains the same.

Colour temperature blackbody (Plancks body): temperature that emits a radiation with the same chromaticity as the radiation taken into consideration.

Cones: photoreceptors of the retina containing light-sensitive pigments that are at the basis of the photopic vision process.

Contrast: subjective adjustment to the apparent difference between two parts of a field of vision (observed simultaneously or sequentially).

Correct specular factor (S1): factor representing the degree of speculra reflection of a wet road surface.

CRI: The color rendering index (IRC o), or in English Color Rendering Index (CRI), ranges from 0 to 100 and is an index that defines the ability of a light source to faithfully reproduce the colors of an illuminated object. The CRI of a led lamp or a led spotlight, to be clear, is a measure of how natural the colors of the objects it illuminates appear. Consequently, the higher the CRI of a luminaire, the more natural the colors of things and objects illuminated by it will appear.

D

Dichroic – An optical phenomenon by which specific transparent minerals present two different colours whether they are looked at by reflection or transparency. In lighting engineering the term indicates special glasses, treated in vacuum chambers with “drugging” gases excited by laser light to obtain the deposit, on the surface, of the layer of the desired colouring. These glasses can resist to high temperatures and last for a very long time: this is the reason why they are used in professional projectors to colour the light beam.

Diffused reflection: diffusion by reflection depending on Lambert Law and in which, on a macroscopic scale, any kind of regular reflection is absent.

Diffuser: device used to vary and control the spatial distribution of radiations by employing exclusively the diffusion phenomenum.

Diffusion: phenomenum by which the spatial distribution of a ray beam changes when the beam is deflected towards multiple directions, from a surface or from a medium, without changing the monochrome components of the frequency.

Digital/Digital Signal – Literally, the action of fingering. In electronics it indicates the building of a signal made of basic elements of Boolean algebra, the bits, information units that can only assume a value comprised between 1 and 0 (on/off). A signal that is built in this way is characterized by a “steps” form, where the number of steps is the number of bits used for the building itself.

Dimmable: A dimmable lamp offers the possibility of increasing and decreasing the intensity of the light, and therefore the brightness, at will and at any time. To do this, it must be equipped with a dimmer, i.e. an electronic regulator (varialuce in Italian) which can be integrated into the lamp itself, or can be managed via:

touch sensor: in this case, to change the intensity of the light, just touch the lamp at a certain point

button: The brightness is changed by pressing and holding or repeatedly pressing a switch

knob: by turning it you can increase or decrease the brightness of a lamp!

Dimmable lamps are certainly much more performing than normal lamps, because they allow you to create different atmospheres in the same environment and because they allow significant energy savings without waste!

Thanks to new electronic technologies, lately it is also possible to manage the intensity of light also thanks to ad hoc applications that can be downloaded on mobile devices such as smartphones and tablets.

Dimmer – Device used to adjust the intensity of a light emitted by a light source. There are electromechanic, electronic or mechanic systems of adjustment, according to the kind of source to be regulated.

Direct flux: on a surface. The light flux received by a surface directly from the devices present in a lighting system.

Direct lighting: lighting with devices having such an intensity distribution that 90 ¸100% of the emitted light flux reaches the working plane directly; assuming that this plane in not infinite.

Direct ratio: of an inddor lighting system. The ratio between the direct flux on the working plane and the total flux directed downwards.

Directional lighting: lighting in which the light on the working plane or on an object mainly originates from a particular direction.

Discharge lamp: lamp in which light is produced, directly or indirectly, by an electric discharge passing through a gas, a metal vapour, or an amalgam of different gases or vapours.

Dissipation – The act and the effect of dissipating or being dissipated; dispersion, dissolution. Dissipation of electricity.

Dispersion:
1) speed variation of the propagation of monochrome radiations in a medium, according to the frequency of such radiations;
2) property of a medium that trigers this phenomenum.

E

Electric discharge: in a gas. The passage of an electric current through gas vapours with the production and movement of charges under the influence of an electric field.

Electricity – A term that indicates the physical phenomenon determined by charges with differing signs, both static (static electricity) and in motion (dynamic electricity) through conducting bodies, capable of producing an energy which man largely exploits to obtain power, light and heat.

Electronics – The science and technique that regards electrons in all their manifestations and applications.

Electrons – Each elementary particle with a negative charge that rotates around the nucleus of the atom, which is charged with positive electricity.

Emergency lighting: lighting envisaged to be used when there is a power failure in the main system.

Energy Class defines the electricity consumption of lamps, spotlights and lighting fixtures.

To differentiate the energy classes, indicators are used, which are present inside the product packaging together with the assembly instructions and any additional technical specifications.

These indicators are: A +++, A ++, A + A ,, B, C, D, E, F, G and range from A +++, which indicates the most performing energy class to G, the least performing, in ascending order.

For all the products in the Store there is the energy class (indicated in the description next to the characteristics themselves).

We are also working on inserting the images of the Energy Class labels for each product!

However, if the image of the energy class is not available in the product gallery, just request it

For lamps with “Bulb excluded”, which can therefore have an Energy Class ranging from A +++ to G according to the choice of the buyer (who inserts the bulb he prefers), we have entered the Energy Class A +, because it is the one that the lamp guarantees (on average) if used with the best bulbs.

In fact, to ensure maximum light output and the best lighting effect of each lamp, our advice is to insert a good quality LED bulb

Energy flux (power) (Fe, F): power emitted, transferred or received as radiation.

Energy spectrum distribution: of a radiation. It represents the spectrum characteristics of a radiation through the relative spectrum distribution of an energy quantity (energy flux …).

Equivalent veil luminance: luminance that must be added, with a superimposition, to the luminance of the background adaptation and of the object in order to create the same threshold of luminance difference that would exist without physiological glare.

F

Field of vision: of the eye(s). Angle amplitude of space in which an object can be perceived when the observer looks at an object placed directly in front of him/her. The field can be either monocular or binocular.

Fluorescence: photoluminescence that persists for a very short time after excitation.

Fluorescent lamp: low pressure mercury-type discharge lamp in which most of the light is emitted by a layer of fluorescent material excited by the ultraviolet radiation created by the discharge.

G

General lighting: substantially uniform lighting of an area or a volume that does not take into consideration particular local needs.

Glare: condition of vision which causes discomfort or the reduction of the visual capability, it is caused by an inadequate distribution or gradient of luminance or by an excessive contrast in space or time.

Glare control index: pure number that denotes the degree with which the discomfort caused by glare is controlled.

Glimmer: attribute of a visual sensation by which a body seems to transmit or reflect in a diffused way a fraction of the cutting light radiation.

Glow discharge: electric discharge in which the secondary emission from the cathode is much bigger than the thermoelectronic emission.

Gobo – A lens-screen device used to screen the exceeding light, which can thus be used to project images with projectors. There are gobos made of thin plates that transmit only full light or shadow; dichroic gobos, which transmit colours too; photographic dichroic gobos, which can reproduce also values of grey. They are made with very complex technologies which range from double-sided etching to laser technologies.

Goniophotometer: photometer used to measure the angle distribution of a light size emitted by a light source, by a luminaire, by a medium or a surface.

KELVIN GRADES: It is the unit of measurement that determines the temperature, or more simply the more or less warm color of the light. The lower the number of degrees in Kelvin the warmer the color of the light. The most common color temperatures (Kelvin) are:

2700K = very warm white light. Provides a relaxed and intimate atmosphere

3000K = warm white light. Not too hot and intense. Pleasant to the eye

4000K = cold white light. Sharp white light.

6500K = daylight. Similar to daylight. Applicable in areas where everything must be clearly visible.

H

Halides – Salt of an halide acid. Bromide, chloride, fluoride and iodide are halides.

Halogen lamp – Lamp that uses an incandescent filament in a saturated environment of gases of chemical elements called “rare earths” to generate light. The quality of the emitted light depends on the frequency with which the discharges take place. The quality of the light projection greatly depends on the optical group that concentrates the emitted rays. Discharge lamps have a colour temperature that ranges from 2,000 to more than 6,500°K according to the type of lamp. Since the light is produced by discharges, the so called “flicker effect”, i.e. an oscillation in the intensity of the emission, can be more or less evident. Discharge lamps generally have a strong emission of ultraviolet rays, which increases as the colour temperature increases.

Height of installation: distance between the reference (or working) plane and the plane where the devices are lying (which is generally coincident with the plane that is tangent with the emission plane).

High bay luminaire: luminaire equipped with a string, chain, tube, by which it can be suspended from the ceiling or another support bearing.

High pressure mercury vapour lamp: mercury vapour lamp, with or without phosphor covering, in which the partial pressure of the vapour during operation equals 105 Pa.

High pressure sodium vapour lamp: sodium vapour lamp in which the partial pressure of vapour during operation equals 104 Pa (e.g. a SOX lamp).

I

Igniter: device employed for the ignition of a discharge lamp (in particular of a fluorescent lamp) which ensures the necessary pre-heating of the electrodes and/or which, combined with the serial feeder, causes an overvoltage.

Illuminance uniformity factor: on a specific plane. Measurement of the illuminance variation on the considered plane, expressed as:
1) ratio between minimum and maximum illuminance;
2) ratio between minimum and average illuminance.

Illuminance (E): on a point of a surface. Ratio between a dF light flux cutting the surface element containing the point and the dA area of the element itself.

Immersiontight luminaire: luminaire presenting an adequate level of sealing against the penetration of liquids in the conditions specified by the relevant regulation (the standard protection degree is IPX7).

Incandescence: emission of light radiation depending on the process of thermal emission.

Incandescent lamp: lamp which produces light by using an element, which is made incandescent by the passage of electricity, that emits visible radiations.

Intensity peak: light intensity of a luminaire on the direction of the beam axes.

Infrared radiation: optical radiation with wavelengths exceeding those of visible radiations.

Interdistance: distance between two successive light centres in a system.

Inverse-square of the distance law: law according to which the illuminance in a point situated on a plane is proportional to the cosine of the angle of incidence (angle between the direction of the incident light and the one perpendicular to the plane), and inversely proportional to the square of the distance between the source and the point.
Isoilluminance curve, isolux curve: locus of the points belonging to a surface on which illuminance acquires the same value.

Isointensity curve: curve graphed on an imaginary sphere with a centre that is coincident with the source, and which links all the representative points of the directions in which light intensity acquires the same values. This curve is represented on a plane projection of the spherical surface.

Isointensity diagram: configuration of isointensity curves.

Isoluminance curve (diagram): locus of the points belonging to a surface on which luminance acquires the same value according to specific positions of the observer and of the source with respect to the surface.

Irradiation or irradiance: in a point comprised on a surface. Ratio between the cutting radiating flux on an element of a surface comprising the point, and the area of the element itself.

J

Joule Effect – Phenomenon by which electricity is transformed in thermal energy.

K

Kinetic – The study of velocity, referred to gases and chemical reactions. It derives from KINETIC which describes movement. Kinetic energy, the energy derived from the velocity of a body such as falling water.

L

Lamp – Device that generates artificial light for lighting purposes.

Lamp utilization factor: ratio between the usable light flux and the light flux emitted by lamps.

Lamp with built-in reflector: lamp in which part of the bulb is covered with reflecting, diffusing or specular material.

Lamp with hot start: lamp with hot cathode that requires the pre-heating of the electrodes that start the unit.

LED: The LED (Light emitting diode in English) is a type of lighting that is now replacing the traditional incandescent and fluorescent lamps, both from the point of view of the quantity of light produced, and above all from the point of view of the energy saving that is obtained. opting for this lighting system.

The LED is a small diode installed on a reflective material, inside which the movements of electron beams inside a material with semiconductor properties produce the ray of light, which is suitably directed outside by a lens. These LEDs are inserted into lighting systems or bulbs, usually small in size and with an attractive design.

However, the LEDs are robust and durable. In fact, these are very compact elements, not made up of glass and thin filaments like traditional light bulbs, and thanks to this, they manage to have a very long life cycle (up to 100,000 hours).

Another aspect that matters is that concerning the energy saving obtained in a LED lighting system: this system in fact requires a very low amount of energy to work, but returns an intense and bright light.

Furthermore, LED lamps work at low voltages, which are safer, and do not heat the bulbs that contain them: this means that LED lamps and bulbs can be handled safely without fear of getting burned!

LED light has now become the advantageous lighting technology, in the long term, also from an economic point of view.

LED lasts 10 times longer than compact fluorescent lights. The light obtained can vary a lot in the shades of colors. Precisely for this reason, the LED has become indispensable and widespread not only in the lighting of homes, but also in cars, motorcycles, in the displays of many electronic accessories and many other fields.

Soon, even the “traditional” LED will be replaced by an even more performing LED technology, the OLED (an organic diode currently used almost exclusively for TV screens and other similar devices).

LED COB and SMD: In the chip-on-board (COB) LED, the individual LEDs are assembled on a single aluminum or ceramic support. This support has a surface of a few square centimeters and can contain hundreds of LED diodes, which once mounted on the support are incorporated with a casting of epoxy resin or silica gel.

When the COB LED is on, the effect is very similar to that of a single light source, thanks to the close fitting of the LEDs. Furthermore, thanks to the positioning of the LED chips, the lumen / space occupied ratio is very favorable. This means that in a very small space it is possible to have very bright LEDs.

To make COB LEDs work, only two contacts and a minimum of components are required: this, together with the lack of an external container present in traditional LED lamps, allows a great reduction in the heat generated. The temperature is attenuated thanks to the ceramic / aluminum base and a heat sink, which is essential that it is proportionate to the LEDs and of good quality, because it is the element that, most of all, guarantees good performance and excellent durability in the led time.

The SMD LED looks like a small plastic shell, inside which the LED chip incorporated with a resin casting is placed. The denomination of the various types of SMD LEDs is given by the dimensions of the casing measured in tenths of a mm (35 × 28, 50 × 50, 57 × 30, etc.). The SMD LED is soldered directly on the electronic board, while the electrical connections are on the side. The light is then emitted from the top.

SMD LEDs ensure better stability over time of the diodes and luminaire luminous performance.

Light intensity diagram: light intensities represented in the form of a diagram or table, in terms of candles per 1000 lumen of lamp flux. The diagram based on the distribution of non-symmetrical light provides the distribution of light of a luminaire on two different planes:
1) a vertical plane passing through the longitudinal axis of the device;
2) a perpendicular plane to the above-mentioned axis.

Note: the light intensity diagram can be used:
a) to provide an approximate idea of the light distribution of the device;
b) to calculate the illuminance values of a point;
c) to calculate the luminance distribution of a device.

Light efficiency (?): of a source. Ratio between emitted light flux and absorbed electrical power.

Light flux (Fv, F): size derived from the radiant energy flux by assessing the radiation on the basis of a selective detector, whose spectrum sensitivi is defined by the normalized visibility spectrum factors (CIE photometric observer of reference).

Light intensity (l): of a source in a given direction. Ratio between the light flux emitted at the source in an element belonging to a solid angle containing the given direction and the element of the solid angle.

Lighting engineering – Lighting technique developed thanks to the increasingly advanced and rational use of new light sources.

Localized lighting: lighting designed to illuminate an area with a higher illuminance in specific positions, for instance the one used as a working plane.

Longitudinal uniformity (Ui): ratio between minimum and maximum luminance as measured along a line that is parallel to the main axis with respect to the observers position.

Low pressure mercury vapour lamp: mercury vapour lamp, with or without phosphor covering, in which the partial pressure of the vapour during operation equals 100 Pa.

Low pressure sodium vapour lamp: sodium vapour lamp in which the partial pressure of vapour during operation equals 5 Pa (e.g. a SOX lamp).

Luminous environment: lighting taken into consideration in relation to its physiological and psychological effect.

Luminaire: object/device that distributes, filters or transforms the light provided by one or more lamps, comprising all the components necessary to fix and protect the lamps and to connect them to the supply circuit.

Luminance (L): (towards the given direction of a real or fictitious surface). Luminance is given by the ratio between the the l emitted light intensity, either reflected or transmitted by the S surface towards the given direction, and the apparent area of the surface itself (the apparent area is the projection of the S surface on the normal plane towards the direction of l intensity):

L = l / S cos a

Luminance contrast (C): between two parts of a field of vision. Relative difference between the luminances of these parts, according to the ratio:

L1 – L2
——— = C
L2
with

C = luminance contrast;
L1 = luminance of the smaller part (object);
L2 = luminance of the bigger part (background).

Luminance distribution curve: curve representing the luminance of a luminaire on a vertical plane depending on the zenith angle.

Luminance factor (b): on the surface element of a body (which is not a source of radiations), towards a given direction, and in specific lighting conditions. Ratio between the luminance of the surface element and that of a perfectly reflecting or transmitting (Lambert) diffuser in the same lighting conditions.

Luminance threshold: the lowest luminance able to induce a perceptible stimulus.

Luminescence: phenomenum of light radiation emission (from atoms, molecules or ions) whose intensity with specific wavelengths or spectrum bands is higher than the thermal radiation that characterises the same material at the same temperature.

Lumen: (indicated by the acronym lm), is a unit of measurement that indicates the total amount of light visible to the human eye, coming from a light source. It is expressed in a number which, usually placed side by side with the wattage of a light bulb, indicates the luminous efficiency of all light bulbs. Clearly, the higher the Lumen in a lamp, the greater the light emitted by the lamp itself. There is no precise rule but to orient yourself just take into account the following principle: For a perfect light output and obtain the maximum possible energy saving, the optimal combination is to have fewer watts absorbed and more lumens emitted. An example? A 10W and 1200 lumen bulb will certainly be more convenient and performing than a 10W but 600 lumen one.

M

MacAdam Ellipses: MacAdam ellipses refer to the area on a chromaticity diagram that contains all the colours which are indistinguishable, to the average human eye, from the colour at the centre of an ellipse. The contour of the ellipse represents the just-noticeable difference of chromaticity.
MacAdam shows the difference between two light sources through ellipses, which are described as having steps’ that indicate the standard deviation of colour. In applications where light sources are visible, this phenomenon should be taken into account because a 3-step ellipse has a lower colour variation than a 5-step ellipse.

Maintenance factor: ratio between the average illuminance on the working plane after a specific duration of use of the installation and the average illuminance obtained in the same conditions with a new installation.

Maintained illuminance: average illuminance on a refence surface measured at the end of a maintenance cycle.

Mesopic vision: intermediate vision between photopic and scotopic vision.

Mercury fluorescent lamp: a high pressure mercury lamp in which the light is partly produced by mercury vapours and by a layer of fluorescent material covering the most internal surface of the external bulb, excited by the ultraviolet radiation created by the discharge.

Mixed light lamp: lamp containing, in the same bulb, a high pressure mercury vapour discharge tube and a filament of an incandescent lamp with series connection. It can either be a diffuser bulb or a bulb covered with a fluorescent material.

Mixer – Device used to summate a number of signals to obtain only one in exit. In lighting engineering the device that makes it possible to control a number of projector with only one signal.

Monochromatic radiation: radiation characterized by only one wavelength. In other words, radiation characterized by a very limited band of wavelengths, so that it can be defined by the indication of only one wavelength.

Moving Head – Projector which is characterized by the fact that it does not have a mirror to shift the light beam (as in the scanner), but which to execute this action moves the whole group that generates the light beam.

Mutual reflection: result of multiple reflections of one radiation on between manifold reflecting surfaces.

N

Nominal mortality rate: number of hours run that pass before a certain percentage of lamps cease to function.

O

Optics – Field of physics that studies light and its correlated phenomena. The term is also used to indicate a set of elements (lens, mirrors, etc.) that comprise – for instance – the section that in a projector generates and concentrates the light.

Opaque medium: medium that does not transmit radiations in the spectrum field of interest.

Optical radiation: electromagnetic radiation having a wavelength comprised between the transition area of X-rays (? = 1 nm) and the transition area of radio waves (? = 1 mm).

Optical efficiency: of a luminaire. Ratio between the total flux emitted by the luminaire, as measured in specified conditions, and the light flux emitted by the lamp(s) that operate without the device in the same specified conditions.

Note: with luminaires employing only incendescent lamps optical efficiency and normal efficiency coincide.

P

Perceived colour: aspect of visual perception that enables an observer to distinguish the differences between two objects that have the same dimensions, form and structure, since these differences are of the same nature as thjose that can be provoked by a different spectrum composition of light (see also page 5).

Perceived colour of an object: perceived colour of an illuminating or luminous object.

Projector – An electric device that projects a very intense beam of light with the aim of illuminating objects that can also be placed at a great distance.

Phosphorescence: luminescence persisting for an appreciable time after excitation.

Photoluminescence: luminescence caused by an absorption of optic radiation.

Photoperiod: natural or artificial cycle of the alternation of light and darkness to which living beings may be exposed.

Photometrics – Branch of optics that studies optical quantities from the point of view of their definition and measurement.

Photometry: measure of the sizes that refer to the radiation assessed according to a given visibility spectrum factor, for instance V (l).

Photons – Elementary particles of radiating energy.

Photopic – In physiology it describes vision in conditions of good luminousness; daylight vision.

Photopic vision: vision experienced when the eye adapts to luminance levels that exceed 3-4 candles per square metre. The cones are considered the main active elements of vision in these conditions.

Phoveal – Small depression in the centre of the macula lutea of the eye where the maximum visual sensibility is recorded.

Physiological glare: type of glare that hinders the vision of objects without necessarily causing discomfort.

Planck radiator: thermal radiator that completely absorbs all incident radiations, regardless of their wavelength, direction of incidence or polarization Such radiator presents, on each wavelength and at a given temperature, the maximum density of spectrum power.

Power supplier: device used with discharge lamps to stabilize the current in the discharge tube, i.e. to adjust the power supply to very low voltage incandescent or discharge lamps to the characteristics of the mains supply.

Power factor: in an electrical circuit. Ratio between the power expressed in watts and the product of the efficient voltage values and current levels. In terms of sinusoidal waveforms, it coincides with the cosine of the angle that expresses the phase difference between voltage and current.

Projector: luminaire that employes the principles of reflection and/or refraction to increase light intensity on a limited solid angle.

Proximal colour temperature: temeprature of Plancks radiator whose perceived apparent colour is the most similar to that of a source referred to having the same luminance and under specific sight conditions.

Psychological glare: type of glare that causes discomfort without necessarily inhibiting the vision of the objects.

R

Radiant energy (Qe, Q): emitted energy, transferred or received as radiation.

Radiation: emission or energy conveyance in the form of electromagnetic waves or particles.

Reference surface: surface on which the illuminance is specified or measured.

Reflector: device used to cause the reflection phenomenum in order to alter the spatial distribution of the light flux coming from a source.

Reflection: transmission of a radiation from a surface, without any wavelength variation, of the monochromatic radiations comprising the radiation.

Reflection factor (r): (of an incident radiation with a spectrum composition, polarization and given geometric distribution). Ratio between the energy or light flux and the cutting flux in the given conditions.

Reflective screen: screen in which the shielding depends essentially on the refraction phenomenum.

Refraction: change of the direction of propagation of a radiation, determined by speed variations of propagation of an optically non-homogeneous medium, or in passing from one medium to another.

Refractor: device used to create the refraction phenomenum in order to alter the spatial distribution of the light flux coming from a source.

Replacement lighting: part of the emergency lighting system that allows to continue normal activity without relevant changes.

Retina: membrane located behind the eye, that is sensitive to light stimuli and which contains photoreceptors (cones and rods) and neuronal cells that transmit a stimulus to the optic nerve.

Rods: photoreceptors of the retina containing light-sensitive pigments capable of starting vision in the dark. Rods are not believed to have any role in the discrimination of colour stimuli.

Note: brilliancy, according to its definition, ia also an attribute of colour. In British recommendations the term brilliancy is used only to describe the brilliancy of colours.

Room index (K): index that is characteristic of the geometry of a room, used to calculate the lamp or luminaire utilization factor.

Note: unless differently indicated, the room index is given by the following formula:
A x b
———- = K
h × (a ÷ b)

with

a = length of the room
b = width
h = heigth of an installation in relation to the centre distance plane.

S

Safety lighting: part of the emergency lighting system designed to guarantee peoples safety.

Saturation: attribute of visual sensation that allows to assess the proportion of chromatically pure colour contained in the total sensation.

Scanner – Term used to indicate a light projector equipped with a mirror that by moving shifts the light beam. The terms comes from the verb to scan, which indicates the action of “searching” typical, for instance, of the sentinel who has a specific area to keep under control.

Scotopic vision: vision experienced when the eye adapts to luminance levels that are below, by a few hundredths, a candle: the rods are considered the main active elements of vision in these conditions. The spectrum appears non-coloured.

Screen: part of a luminaire made up of translucent or opaque elements, geometrically arranged in order to hide the lamps from the observer from specific angles.

Service lighting: that part of the emergency lighting system designed to ensure that it is possible to efficiently identify and use a way ouy in the case of non-functioning of the normal lighting system.

Solid angle (O): solid angle created in the centre of a sphere by drawing a line that goes from the dome of an area which is numerically equal to the square of the radius.

Specific luminaire index (SLI): size index of a luminaire glare control fitness.

Specular or regular reflection: reflection, without diffusion, depending on the laws of geometrical optics, usable for mirrors.

Specular reflector: part of a luminaire designed to reflect the light flux of lamps towards the required direction, through specular reflection.

Spectrum distribution:
a) of a photometric quantity:spectrum distribution of the photometric quantity according to the wavelength;
b) of a radiometric quantity (ray flux/radiant flux, ray intensity …):spectrum distribution of the radiometric quantity depending on the wavelength.

Spectrum locus: locus of the points, belonging to a chromaticity diagram or to a three-fold stimulus space, that represent the monochromatic stimuli.

Speed of perception: reciprocal of the minimum exposition time that an object requires to be perceived.

Spill light: flux that is dispersed because of the scattering phenomenum.

Splash-protected luminaire: luminaire built in order to prevent that it is damaged by direct splashes coming from any direction (the standard protection degree is IPX5).

Start device: electric device that creates the necessary conditions to start a discharge.

Steradian (sr): SI unit derivative of a solid angle:a solid angle that, by having its apex in the centre of a sphere, cuts an area of the spheric surface that equals the area of a square having the radium of the sphere as its side.

Symmetrical light intensity distribution: of a source. Light intensity distribution having at least one axis or plane of symmetry.

T

Thermal radiation: emission process in which the radiating energy is created by the thermal agitation in the particles comprising the matter (atoms, molecules, ions).

Threshold increment (TI): number indicating the degree of control of physiological glare.

Note: such value depends on the field of observation, the time of adaptation and the conditions of observation.

Tilt angle: tilt angle calculated upwards in relation to the horizontal of a luminaire.

Tint: attribute of a visual sensation according to which a surface appears to be similar to one of the perceived colours (red, yellow, green and blue, or a combination of two of them).

Total uniformity (Uø): ratio between the minimum and average luminance value of the area taken into consideration.

Transmission: passage of a radiation through a medium, without variations of frequency of the monochromatic radiations that comprise it.

Transmission factor: (of an incident radiation with a spectrum composition, polarization and given geometric distribution). Ratio between the transmitted energy or light flux and the cutting flux in the given conditions.

U

Ultraviolet radiation: optical radiation with wavelengths that are lower than those of the visible radiation. In the range between 100 and 400 nm the ultraviolet radiation is generally indicated using the symbols UVA between 315 and 400 nm, UVB between 280 and 315 nm and UVC between 100 and 280 nm.

UGR: The UGR (Unified Glare Rating) is a scale of values used to classify the glare produced by light sources, and is applied for the lighting design of interior environments. The UGR is therefore a unified index in the international field for the assessment of direct annoying glare, and is subject to European and national regulations that establish the limits allowed in the workplace. In Italy, for example, the UNI 11165: 2005 standard applies, which indicates the criteria for calculating the unified glare index deriving from artificial light sources.

The calculation of the UGR takes into consideration various factors, including the light output of the lamps, their arrangement in the environment, the distance between the light sources and the observer, and the characteristics of the environment itself (size and index of reflection).

However, for each application area, a UGR lower than a certain value is recommended, which varies in relation to the need for quality lighting and the time spent in an environment.

Consequently, for each place to be illuminated there must be different UGR levels. On average, the ranges not to be exceeded for each environment are as follows:

Up to 16 UGR for technical drawing laboratories and operating theaters.

Up to 19 UGR for offices, libraries and classrooms

Up to 22 UGR for precision work and factory or warehouse work

Up to 25 UGR for general lighting of factories or warehouses

Up to 28 UGR for more general lighting (warehouses, construction sites, tracks, etc.)

Following this general scheme therefore serves to avoid glare and useless eye strain with consequent fatigue.

Uniform color scale (UCS): color scale in which the coordinatesscales are chosen so that, in all the parts of the scale, equal intervals represent, as far as possible, equal variations in the discrimination of colors having the same luminance (see also page 6).

Unit of measurement: candle, cd.

Unit of measurement: cd ? m-2.

Unit of measurement: joule. J = W·s.

Unit of measurement: Kelvin, K.

Unit of measurement: lumen, lm.

Unit of measurement: lumen/watt, lm/W.

Unit of measurement: lux, lx.

Note: it is better to avoid using the expression depreciation factor as a synonym of maintenance factor.

Unit of measurement: metre, m.

Unit of measurement: steradian, sr.

Unit of measurement: watt, W.

Unit of measurement: W/m2

Note: the light intensity of luminaires is generally represented ina diagram of the light intensity or in a idocandle diagram.

Usable flux: light flux received by one side of the reference surface taken into consideration.

Utilization factor (U): ratio between usable light flux and the light flux coming out of the device.

Note: it is better to avoid the expression utilization coefficient.

V

Vcurve (?): curve of the visibility spectrum factor for scotopic vision.

Vapour halogen lamp: discharge lamp in which light is produced by the radiation of a metal mixed vapours (e.g. mercury) and the products of the dissociation of halogens (e.g. thallium, indium or sodium).

Vapourproof luminaire: luminaire built in order to resist the penetration of vapours or gases (the standard protection degree is IPX6).

Visibility spectrum factor curve: curve that provides the relative sensitivity (V) of the standard CIE photometric observer for monochromatic radiations depending of the wavelength:

a) for photopic vision, V curve (?);
b) for scotopic vision, Vcurve (?).

Visual acuity:
1) qualitatively:capability to perceive distinctly objects that are very close to each other;
2) quantitatively:reciprocal of the value (expressed in arc minutes) of the minimum angle at which the eye perceives that two objects (points or lines) placed close to each other, are distinct and separate.

Visual angle: angle created by an object against the observation point; it is generally measured in arc minutes.

Visual contrast threshold: minimum perceived value of the the contrast in a given condition of eye adaptation.

Visual performance: degree of efficacy of the visual system measured for instance through the speed and precision with which a visual task is carried out.

Voltage – In electrical engineering, the difference of potential between two points. The intensity is measured in Volts (V).

Volt – (V) Unit of measurement of the electromotive force. From Alessandro Volta, the inventor of the battery.

W

Water-resistant luminaire: luminaire built in order to resist the penetration of rain and usually employed in exterior lighting (the standard protection degree is IPX2, 3, 4).

Watt – (W) The watt (symbol W) is the fundamental unit of measurement of electrical power according to the international system, and is used to measure both the maximum power of an electrical device and to indicate the production of a plant. The watt is a fairly small unit of measurement, which is why its multiples are often used, especially in everyday objects and domestic users. The watt in lighting is also the unit of measurement of the power of the light produced by the bulbs.

However, a 40-watt bulb produces less light, and consumes less than a 100-watt bulb because it has less power. The watt is therefore not the unit of measurement of light intensity, which is measured in lumens. This difference is particularly important in energy-saving light bulbs and LEDs, which use very little energy, so they have extremely low power, compared to traditional light bulbs, while still producing the same amount of light.

Wavelength (?): distance between two successive points, on the direction of propagation of a periodic wave, on which the obscillation presents the same phase (it occurs at the same time).

Working plane: reference surface defined as the plane on which a task is usually carried out.

Z

Zone light flux diagram: graphic representation of the distribution of the light flux of a luminaire or lamp, in which the light flux emitted from inside a cone is expressed according to the half angle of the cone opening.