Glossary - E

E 

effective ceiling cavity reflectance, a number giving the combined reflectance effect of the wall and ceiling reflectance of the ceiling cavity. See ceiling cavity ratio. 

efficacy† See luminous efficacy of a source of light and spectral luminous efficacy of radiant flux. 

efficiency† See luminaire efficiency, luminous efficacy of a source of light, and spectral luminous efficiency of radiant flux. 

egress lighting† emergency lighting for egress. 

electric discharge† See arc discharge, gaseous discharge, and glow discharge. 

electric-discharge lamp a lamp in which light (or radiant energy near the visible spectrum) is produced by the passage of an electric current through a vapor or gas. See carbon arc lamp, cold-cathode lamp, fluorescent lamp, glow lamp, high intensity discharge (HID) lamp, and hot cathode lamp. 

Note Electric-discharge lamps can be named after the filling gas or vapor that is responsible for the major portion of the radiation, for example, mercury lamps, sodium lamps, neon lamps, and argon lamps. A second method of designating the electric-discharge lamps is by physical dimensions of operating parameters, for example, short-arc lamps, high-pressure lamps, and low-pressure lamps. A third method of designating electric discharge lamps is by their application. In addition to lamps for illumination there are photochemical lamps, bactericidal lamps, blacklight lamps, sun lamps, and others. 

electromagnetic spectrum† a continuum of electric and magnetic radiation encompassing all wavelengths. See regions of the electromagnetic spectrum. 

emergency† any condition, external or internal to the premises, that compromises the effectiveness of the lighting in an occupied area for safe movement within and out of that area and safe operation of equipment within the space. An emergency can include any or all of the following: 

Utility power failure; Utility power voltage reduction (brownout) below the minimum required to support the arc in fluorescent or HID lamps   Power interruption within the premises including total power loss or individual phase or branch circuit failure   Fire or smoke. 

emergency lighting designed to supply illumination essential to the safety of life and property in the event of failure of the normal supply. 

emissivity, ε the ratio of the radiance (for directional emissivity) or radiant exitance (for hemispherical emissivity) of an element of surface of a temperature radiator to that of a blackbody at the same

emittance, ε The ratio of radiance in a given direction (for directional emittance) or radiant exitance (for hemispherical emittance) of a sample of a thermal radiator to that of a blackbody radiator at the same temperature. 

enclosed and gasketed† See vapor-tight luminaire. 

equal interval (isophase) light a rhythmic light in which the light and dark periods are equal. 

equipment operating factor the ratio of the lumens of a high-intensity discharge (HID) lamp-ballastluminaire combination in a given operating position to the lumens of the lamp-ballast-luminaire combination (a) operated in the position for rating lamp lumens, and (b) using the standard (reference) ballasting specified for rating lamp lumens.  Note If the given lamp operating position is not the same as the lamp rating position, the lumens ratio for the operating ballast to standard rating ballast is determined in the given operating position. This ratio is multiplied by the lamp position factor to obtain the equipment operating factor. 

explosion-proof luminaire a luminaire that is completely enclosed and capable of withstanding an explosion of a specific gas or vapor that can occur within it, and preventing the ignition of a specific gas or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within. It must operate at such an external temperature that a surrounding flammable atmosphere is not ignited thereby. 

Glossary - D

D 

dark adaptation the process by which the retina becomes adapted to a luminance less than about 0.034 cd/m2 = 2.2 × 10−5 cd/in.2 = 0.01 fL. 

daylight availability the luminous flux from sun plus sky at a specific location, time, date, and sky condition. 

daylight factor a measure of daylight illuminance at a point on a given plane, expressed as the ratio of the illuminance on the given plane at that point to the simultaneous exterior illuminance on a horizontal plane from the whole of an unobstructed sky of assumed or known luminance distribution. Direct sunlight is excluded from both interior and exterior values of illuminance. 

daylight lamp a lamp producing a spectral distribution approximating that of a specified daylight. 

dichroic filter† a filter that transmits certain wavelengths and reflects those not transmitted; 

diffuse reflectance the ratio of the flux leaving a surface or medium by diffuse reflection to the incident flux. 

Note Provision for the exclusion of regularly reflected flux, which is nearly always present, must be clearly described. 

diffuse reflection that process by which incident flux is redirected over a range of angles. 

diffuse transmission that process by which the incident flux passing through a surface or medium is scattered. 

diffuse transmittance the ratio of the diffusely transmitted flux leaving a surface or medium to the incident flux. 

Note Provision for the exclusion of regularly transmitted flux must be clearly described. 

diffused lighting provided on the work plane or on an object that is not incident predominantly from any particular direction. 

diffuser a device to redirect or scatter light from a source, primarily by the process of diffuse transmission. 

diffusing panel a translucent material covering the lamps in a luminaire in order to reduce the brightness by distributing the flux over an extended area. 

diffusing surfaces and media those surfaces and media that redistribute at least some of the incident flux by scattering. See complete diffusion, incomplete diffusion, narrow-angle diffusion, perfect diffusion, and wide-angle diffusion. 

dimmer a device used to control the intensity of light emitted by a luminaire by controlling the voltage or current available to it. 

direct glare resulting from high luminances or insufficiently shielded light sources in the field of view. It is usually associated with bright areas, such as luminaires, ceilings, and windows, that are outside the visual task or region being viewed. A direct glare source can also affect performance by distracting attention. 

direct-indirect lighting a variant of general diffuse lighting in which the luminaires emit little or no light at angles near the horizontal. 

direct lighting lighting involving luminaires that distribute 90 to 100% of the emitted light in the general direction of the surface to be illuminated. The term usually refers to light emitted in a downward direction.

direct ratio the ratio of the luminous flux that reaches the floor of a room cavity directly to the downward component from the luminaire. 

directional lighting lighting provided on the workplane or on an object. Light that is predominantly from a preferred direction. See accent lighting, key light, and cross light. 

disability glare the effect of stray light in the eye whereby visibility and visual performance are reduced. A direct glare source that produces discomfort can also produce disability glare by introducing a measurable amount of stray light in the eye. 

disability glare factor (DGF) a measure of the visibility of a task in a given lighting installation in comparison with its visibility under reference lighting conditions, expressed in terms of the ratio of luminance contrasts having an equivalent effect upon task visibility. The value of the DGF takes account of the equivalent veiling luminance produced in the eye by the pattern of luminances in the task surround. 

discomfort glare† glare that produces discomfort. It does not necessarily interfere with visual performance or visibility. 

discomfort glare factor the numerical assessment of the capacity of a single source of brightness, such as a luminaire, in a given visual environment for producing discomfort (this term is obsolete and is retained only for reference and literature searches). See glare and discomfort glare. 

discomfort glare rating (DGR) a numerical assessment of the capacity of a number of sources of luminance, such as a luminaire, in a given visual environment for producing discomfort. See discomfort glare factor. See also Chapter 9, Lighting Calculations. 

distal stimuli in the physical space in front of the eye one can identify points, lines and surfaces, and three-dimensional arrays of scattering particles that constitute the distal physical stimuli that form optical images on the retina. Each element of a surface or volume to which an eye is exposed subtends a solid angle at the entrance pupil. Such elements of solid angle make up the field of view, and each has a

specifiable luminance and chromaticity. Points and lines are specific cases that have to be dealt with in terms of total intensity and intensity per unit length. Distal stimuli are sometimes referred to simply as lights or colors. 

downlight a small direct lighting unit that directs the light downward and can be recessed, surfacemounted, or suspended. 

downward component that portion of the luminous flux from a luminaire that is emitted at angles below the horizontal. See upward component. 

dust-proof luminaire a luminaire so constructed or protected that dust does not interfere with its successful operation. 

dust-tight luminaire a luminaire so constructed that dust does not enter the enclosing case.

Glossary - C

C 

candela, cd the SI unit of luminous intensity, equal to one lumen per steradian (lm/sr).

ceiling area lighting a general lighting system in which the entire ceiling is, in effect, one large luminaire. 

Note Ceiling area lighting includes luminous ceilings and louvered ceilings. 

ceiling cavity the cavity formed by the ceiling, the plane of the luminaires, and the wall surfaces between these two planes. 

ceiling cavity ratio (CCR) a number computed by using the distance from the plane of the luminaire to the ceiling (hc) as Heightcavity in the equations given for cavity ratio. 

ceiling projector a device designed to produce a well-defined illuminated spot on the lower portion of a cloud for the purpose of providing a reference mark for the determination of the height of that part of the cloud.  

ceiling ratio the ratio of the luminous flux reaching the ceiling directly to the upward component from the luminaire. 

channel an enclosure containing the ballast, starter, lamp holders, and wiring for a fluorescent lamp. Can also be a similar enclosure on which filament lamps (usually tubular) are mounted. 

chromatic color perceived color possessing a hue. In everyday speech, the word color is often used in this sense in contradistinction to white, gray, or black. 

chromatic contrast threshold (color contrast threshold) a threshold of chromaticity difference between two patches of color juxtaposed and separated only by a color contrast border, below which they cannot be perceived as different in chromaticness or separated by a contrast border. A contrast border can involve differences both in luminance and in chromaticity between the sides. 

chromaticity coordinates of a color, x, y, z the ratios of each of the tristimulus values of the color to the sum of the three tristimulus values. 

chromaticity diagram a plane diagram formed by plotting one of the three chromaticity coordinates against another. 

chromaticity difference threshold the smallest difference in chromaticity between two colors of the same luminance that makes them perceptibly different. The difference can be a difference in hue or saturation, or a combination of the two. 

chromaticity of a color the dominant or complementary wavelength and purity aspects of the color taken together, or of the aspects specified by the chromaticity coordinates of the color taken together. 

chromaticness† the attribute of a visual sensation according to which the (perceived) color of an area appears to be more or less chromatic. 

clear sky a sky that has less than 30% cloud cover. 

cloudy sky a sky that has more than 70% cloud cover. 

coefficient of utilization (CU) the ratio of luminous flux (lumens) calculated as received on the work plane to the total luminous flux (lumens) emitted by the lamps alone. It is equal to the product of room utilization factor and luminaire efficiency. See Chapter 9, Lighting Calculations. 

coffer a recessed panel or dome in the ceiling. 

cold-cathode lamp an electric-discharge lamp whose mode of operation is that of a glow discharge and that has electrodes so spaced that most of the light comes from the positive column between them. 

color† the characteristic of light by which a human observer can distinguish between two structure-free patches of light of the same size and shape. See light source color and object color.  

color rendering† a general expression for the effect of a light source on the color appearance of objects in conscious or subconscious comparison with their color appearance under a reference light source. 

color rendering improvement (of a light source)† the adjustment of spectral composition to improve color rendering. 

color rendering index (of a light source) (CRI) a measure of the degree of color shift objects undergo when illuminated by the light source as compared with those same objects when illuminated by a reference source of comparable color temperature. 

color temperature of a light source the absolute temperature of a blackbody radiator having a chromaticity equal to that of the light source. See also correlated color temperature and distribution temperature. 

colorfulness of a perceived color the attribute according to which it appears to exhibit more or less chromatic color. For a stimulus of a given chromaticity, colorfulness normally increases as the absolute luminance is increased. 

cornice lighting lighting comprising sources shielded by a panel parallel to the wall and attached to the ceiling and distributing light over the wall. 

correlated color temperature (of a light source) (CCT) the absolute temperature of a blackbody whose chromaticity most nearly resembles that of the light source. 

cosine law a law stating that the illuminance on any surface varies as the cosine of the angle of incidence. The angle of incidence is the angle between the normal to the surface and the direction of the incident light. The inverse square law and the cosine law can be combined as E = (I cos θ)/d². See cosinecubed law and inverse square law. 

cove lighting comprising sources shielded by a ledge or horizontal recess, and distributing light over the ceiling and upper wall. 

cucoloris an opaque cutout panel mounted between a light source (sun or arc) and a target surface in order to project a shadow pattern (clouds or leaves are typical) upon scenery, cyclorama, or acting area. 

cutoff angle (of a luminaire) the angle, measured up from nadir, between the vertical axis and the first line of sight at which the bare source is not visible. 

Glossary - B

B 

back light illumination from behind (and usually above) a subject to produce a highlight along its edge and consequent separation between the subject and its background. See side-back light. 

backing lighting the illumination provided for scenery in off-stage areas visible to the audience. 

baffle a single opaque or translucent element to shield a source from direct view at certain angles, to absorb or block unwanted light, or to reflect and redirect light. 

balcony lights luminaires mounted on the front edge of an auditorium balcony. 

barn doors a set of adjustable flaps--usually two, four, or eight--which can be attached to the front of a luminaire (usually a Fresnel spotlight) in order to partially control the shape and spread of the light beam. 

base light uniform, diffuse, near-shadowless illumination sufficiently intense for a television or film picture of acceptable quality at a desired lens opening. Acceptable base level of unaccented stage illumination. 

beacon a light (or mark) used to indicate a geographic location. See aerodrome beacon, aeronautical beacon, airway beacon, approach-light beacon, hazard or obstruction beacon, identification beacon, and landmark beacon. 

beam angle the angle between the two directions for which the intensity is 50% of the maximum intensity as measured in a plane through the nominal beam centerline. For beams that do not possess rotational symmetry, the beam angle is generally given for two planes at 90°, typically the maximum and minimum angles. 

Note In certain fields of application, the beam angle was formerly measured to 10% of maximum intensity. 

beam axis of a projector a line midway between two lines that intersect the intensity distribution curve at points equal to a stated percentage of its maximum (usually 50%). 

beam lumens the total flux in that region of space where the intensity exceeds 50% of the maximum intensity. 

beam projector a luminaire with the light source at or near the focus of a paraboloidal reflector, producing near-parallel rays of light in a beam of small divergence. Some are equipped with spill rings to reduce spill and glare. In most types, the lamp can be moved toward or away from the reflector to vary the beam spread. 

beam spread (in any plane) the angle between the two directions in the plane in which the intensity is equal to a stated percentage of the maximum beam intensity. 

blackbody a temperature radiator of uniform temperature whose radiant exitance in all parts of the spectrum is the maximum obtainable from any temperature radiator at the same temperature. Such a radiator is called a blackbody because it absorbs all the radiant energy that falls upon it. All other temperature radiators can be classed as nonblackbodies. Nonblackbodies radiate less in some or all wavelength intervals than a blackbody of the same size and the same temperature. 

Note The blackbody is practically realized over limited solid angles in the form of a cavity with opaque walls at a uniform temperature and with a small opening for observation. It is variously called a standard radiator, an ideal radiator, or a complete radiator. 

blackbody (planckian) locus the locus of points on a chromaticity diagram representing the chromaticities of blackbodies having various (color) temperatures. 

black light the popular term for UV energy near the visible spectrum. 

Note For engineering purposes the wavelength range 320 to 400 nm has been found useful for rating lamps and their effectiveness upon fluorescent materials (excluding phosphors used in fluorescent lamps). By confining black light applications to this region, germicidal and erythemal effects are, for practical purposes, eliminated. 

black-light flux radiant flux within the wavelength range 320 to 400 nm. It is usually measured in milliwatts. See fluoren. 

Note The floren is used as a unit of black-light flux and is equal to one milliwatt of radiant flux in the wavelength range 320 to 400 nm. Because of the variability of the spectral sensitivity of materials irradiated by black light in practice, no attempt is made. 

blending lighting general illumination used to provide smooth transitions between the specific light areas on a stage. 

blinding glare glare that is so intense that for an appreciable length of time after it has been removed, no object can be seen. 

bollard† luminaires having the appearance of a short, thick post, used for walkway and grounds lighting. The optical components are usually top-mounted. 

borderlight a long continuous striplight hung horizontally above a stage and aimed down to provide general diffuse illumination or to light the cyclorama or a drop; usually wired in three or four color circuits. Also available in portable versions. 

bracket (mast arm) an attachment to a lamp post or pole from which a luminaire is suspended. 

brightness (of a perceived aperture color) the attribute by which an area of color of finite size is perceived to emit, transmit, or reflect a greater or lesser amount of light. No judgment is made as to whether the light comes from a reflecting, transmitting or self-luminous object. See also brightness of a perceived light source color, luminance, subjective brightness, and veiling brightness. 

brightness contrast threshold when two patches of color are separated by a brightness contrast border as in the case of a bipartite photometric field or of a disk-shaped object surrounded by its background, the border between the two patches is a brightness contrast border. The contrast that is just detectable is known as the brightness contrast threshold. 

brightness of a perceived light source color† the attribute in accordance with which the source seems to emit more or less luminous flux per unit area.  

Glossary - A

A 

absolute luminance threshold luminance threshold for a bright object like a disk on a totally dark background. 

absorption a general term for the process by which incident flux is converted to another form of energy, usually and ultimately to heat.  All of the incident flux is accounted for by the processes of reflection, transmission, and absorption. 

accent lighting directional lighting to emphasize a particular object or surface feature or to draw attention to a part of the field of view. See directional lighting. 

acceptance half-angle† the acceptance half-angle is set by the refractive indices of the core and cladding of fiber optics, and it is expressed in terms of the numerical aperture (NA). The numerical aperture is given as NA = n0 sin p.† 

accommodation the process by which the eye changes focus from one distance to another. 

actinic a term meaning photochemically active. 

action spectrum the quantitative actinic response of a chemical or biological substance or living organism as a function of an appropriate spectral parameter such as wavelength or photon energy. 

adaptation the process by which the retina becomes accustomed to more or less light than it was exposed to during an immediately preceding period. It results in a change in the sensitivity to light. See scotopic vision, photopic vision, and chromatic adaptation. 

Note Adaptation is also used to refer to the final state of the process, such as reaching a condition of adaptation to a specific luminance level. 

adaptive color shift the change in the perceived object color caused solely by change of the state of chromatic adaptation. 

ambient lighting lighting throughout an area that produces general illumination.  

ampere† the intensity of electrical current flow. The symbol often used in equations is I, although A is also acceptable. 

angstrom,ņ a unit of wavelength equal to 10−10 m (one ten-billionth of a meter).

aperture color† the perc0eived color of the sky or of a patch seen through an aperture and not identifiable as belonging to a specific object. 

apostilb (asb) a lambertian unit of luminance equal to 1/π = 0.3183 cd/m2. This term is obsolete, and its use is deprecated. 

arc discharge an electric discharge characterized by high cathode current densities and a low voltage drop at the cathode. 

Note The cathode voltage drop is small compared with that in a glow discharge, and secondary emission plays only a small part in electron emission from the cathode. 

arc lamp a discharge lamp in which the light is emitted by an arc discharge or by its electrodes. 

Note The electrodes can be either of carbon (operating in air) or of metal. 

artificial pupil a device or arrangement for confining the light passing through the pupil of the eye to an area smaller than the natural pupil. 

average luminance luminance is a property of a geometric ray. Luminance as measured by conventional meters is averaged with respect to two independent variables, area and solid angle; both must be defined for a complete description of a luminance measurement. 

Glossary of lighting

Dear Reader,

Its been a way too long since I ever thought of posting anything on my blog. Had a few job change and travelled to a lot of different places which kept me away from blogging. 

But now lets begin.

The glossary list has been extracted from IESNA Lighting Handbook. A lot of terms has been removed only to match the objective of the series blog that I have planned for.

Most of the definitions in this glossary have been directly used from ANSI/IES RP-16-1996, Nomenclature and Definitions for Illuminating Engineering. Those marked with a dagger (†) do not appear in the ANSI standard. 

One of a Lighting Simulation Project

Hi,

This picture here below is a Lighting Simulation of one of the floors of a building. Its complicated boundaries were intriguing. more than 20 different types of luminaires were used in this project.