DEFINITION OF LIGHTING TERMS

ABSORPTANCE - Ratio of the flux absorbed by a medium to the incident flux.
ABSORPTION - General term for the process by which incident flux is dissipated.
ACCENT LIGHT - Directional lighting to emphasize a particular object or draw attention to a part of the field of view. visit http://philarchreview.blogspot.com/
ALTITUDE - Angular distance between the vertical plane containing the sun and the plane of the meridian.
BAFFLE - A single opaque or translucent element to shield a source from direct view at certain angles or to absorb unwanted Light.
BALLAST - Device used with electric discharge lamp to obtain the necessary circuit conditions for starting and operating. visit http://philarchreview.blogspot.com/
BLACK LIGHT - Popular term for ultraviolet energy near the visible spectrum.

BRIGHTNESS - The terms Brightness and Luminance are almost entirely interchangeable, with the latter being the newer term (See Luminance)
CANDELA - The unit of luminous intensity.
CANDLE POWER - Luminous intensity expressed in candelas.
CEILING AREA LIGHTING - General lighting system in which the entire ceiling is, in effect, one
large luminary, as in louvered ceilings and luminous ceilings.
CEILING CAVITY - Cavity can formed by the ceiling, the plane of the luminaries, and the wall surfaces between these two planes.
CHANNEL - Enclosure containing the ballast, starter, lamp holders, and wiring for
a fluorescent lamp.
CLEAR SKY - Sky having less than 30% cloud cover.
CLERESTORY - Part of a building rising clear of the roofs and whose walls contain
windows for lighting the interior.
COEFFECIENT OF
UTILIZATION - Ratio of the luminous flux (lumens) from a luminaire received on the
work plane to the lumens emitted by the luminaire’s alone.
DAYLIGHTING FACTOR - Ratio of the daylight illuminance on a plane to the exterior illuminance on a horizontal plane from the whole of an obstructed sky assumed or known luminance.
COLD-CATHODE LAMP - Electric discharge lamp of the glow discharge type.
CORNICE LIGHTING - Lighting by means of light sources shielded by a plane parallel to the wall and attached to the ceiling that distribute light over the wall.
COVE LIGHTING - Lighting by means of sources shielded by a ledge or horizontal recess that distribute light over the ceiling and upper wall.
CUT OFF ANGLE (OF A LUMUNAIRE) - The angle, measured up from the nadir, between the vertical axis and the first line of sight at which the bare source not visible.
DIFFUSE REFLECTANCE - Ratio of the flux leaving a surface or medium by diffuse reflection to the incident flux.
DIFFUSE REFLECTION - Process by which the incident flux is redirected over a range of angles.
DIFFUSE TRANSMISSION - Process by which the incident flux passing through a surface or medium is scattered.
DIFFUSE TRNSMITTANCE - Ratio of the diffusely transmitted flux leaving a surface or medium to the incident flux.
DIFFUSE LIGHTING - Light that is not predominantly incident from any particular direction.
DIFFUSER - Device to redirect or scatter the light from a source, primarily by the
process of diffuse transmission.
DIRECT-INDIRECT LIGHTING - Variant of general diffuse lighting in which the luminaries emit little or no light at angles near the horizontal.
DIRECT LIGHTING - Lighting by luminaries distributing 90 to 100% of the emitted lightin the direction (usually downward) of the surface to be illuminated.
DISSABILITY GLARE - Glare resulting in reduced visual performance and visibility.
DISCOMFORT GLARE - Glare producing discomfort but not necessarily impairing visualperformance or visibility.
LAMP - Lamp in which light is produced by the passage of an electric currentthrough a vapor or gas, as in fluorescent, cold-cathode, and mercurylamps.
FENESTRATION - Any opening or arrangement of openings (normally filled with mediafor control) for the admission of daylight.
FILTER - Device for changing, by transmission, the magnitude and /or the spectral composition of the flux incident upon it.
FLOODLIGHT - Projector designed for lighting a scene or object to a luminance considerably greater than its surroundings.
FLOOR CAVITY - Cavity formed by the work plane, the floor, and the wall surfacesbetween these two planes.
FLOURESCENT LAMP - Low- pressure mercury electric discharge lamp in which a fluorescingcoating (phosphor) transforms some of the ultraviolet energy generated by the discharge into light.
FLUSH-MOUNTED OR RECESSED - Luminaire mounted above the ceiling with the opening of the luminaire flush with the surface of the ceiling.
FOOTCANDLE (fc) - The unit of illumination. The illumination on a surface 1 sq. ft. in area on which there is a uniformly distributed flux of 1 lumen.
FOOTLAMBERT (fl) - Unit of luminance; the luminance of a perfectly diffusing surface emitting or reflecting light at the rate of 1 lumen per sq. ft. The luminance in foot lamberts of any reflecting surface is the product of
the illumination in foot candles and the luminous reflectance of the surface.
GASEOUS DISCHARGE - Emission of light from gas atoms excited by an electric current.
GENERAL DIFFUSE LIGHTING - Lighting by luminaries distributing 40 to 60% of the emitted light downward and the balance upward and horizontally.
GLARE - Sensation produced by luminance within the visual field sufficiently greater than the luminance to which the eyes are adapted to cause annoyance, discomfort, or loss in visual performance and visibility.
ILLUMINANCE - The density of the luminous flux incident on a surface.
INDIRECT LIGHTING - Lighting by luminaries distributing 90 to 100% of the omitted light upward.
INFRARED RADIATION - Radiant energy within the wavelength range 770 to 10 to the 6 power nanometers.
INSTANT START FLOURESCENT LAMP - One designed to start by high voltage without preheating of the electrodes.
LAMP - Related term for a man-made source of light.
LASER - Acronym for light amplification by stimulated emission of radiation. highly monochromatic and coherent beam with a steady oscillation.
LIGHT LOSS FACTOR (LLF) - Factor used in calculating level of illumination after a period of time.it takes into consideration temperature and voltage variations, dirt
accumulation, lamp depreciation, etc.
LOUVER - Series of baffles used to shield a source from view at certain angles.
LOUVER SHIELDING ANGLE - Angle between the horizontal plane of baffles or louver grid and the plane at which the louver conceals all objects above.
LUMEN (LM) - The unit of luminous flux.
LUMINAIRE - Complete lighting unit consisting of a lamp or lamps together with the parts designed to distribute the light, to position and protect the lamps, and to connect the lamps to the power supply.
LUMINAIRE EFFECIENCY - Ratio of luminous flux emitted by a luminaire to that emitted by the lamp or lamps used therein.
LUMINANCE (Photometric Brightness) - The luminous intensity of a surface in a given direction per unit of
projected area of the surface as viewed from that direction.
LUMINOUS CEILING - Ceiling area lighting system comprising a continuous surface at diffuse transmitting material with light sources mounted above it.
LUMINUOUS DENSITY - Quantity of light per unit volume.
LUMINOUS EFFICACY OF A SOURCE OF LIGHT - Quotient of the total luminous flux emitted by the total lamp power input expressed in lumens per watt.
LUMINOUS FLUX - The time rate of flow of light.
LUX (lx) - The SI (metric) unit of illuminance . One lux is one lumen per sq. meter.
MAINTENANCE FACTOR - Same as Light Loss Factor
MERCURY LAMP - Electric discharge lamp in which the major portion of the radiation is produced by excitation of mercury atoms.
MOUNTING HEIGHT ABOVE
THE WORK PLANE - Distance from the work plane to the light center of the luminaire or to the plane of the ceiling for recessed equipment.
PARTLY CLOUDY SKY - One that has 30 to 70% cloud cover.
ORIENTATION - Position of a building with respect to compass direction.
OVERCAST SKY - One that has 100% cloud cover; the sun is not visible.
POLARIZATION - Process by which the transverse vibration of light waves are orientedin a specific plane.
PREHEAT (Switch Start)
FLOURESCENT LAMP - One designed for operation with a ballast that provides for preheating the electrodes in order to start the arc.
RAPID-START FLOURESCENT
LAMP - One designed for operation with a ballast that provides for heating the electrodes and initiating the arc without a starting switch or the application of high voltage.
REFLECTANCE OF A SURFACE OR MEDIUM - Ratio of the reflected flux to the incident flux .
REFLECTED GLARE - Glare resulting from specular reflections of high luminances in polished or glossy surfaces in the field of view, especially within or in close proximity to the visual task.
REFLECTION - Process by which the incident flux leaves a surface or medium from the incident side.
REFLECTOR - Device used to redirect the luminous flux from a source by the process of reflection.
REFRACTION - Process by which the direction of a ray of light changes as it passes obliquely from one medium to another in which its speed is different.
REGRESSED LUMINAIRE - One mounted above the ceiling with the opening of the luminaire above ceiling line.
ROOM CAVITY - Cavity formed by the plane of the luminaries, the work plane and thewall surfaces between these two planes.
SEMI-DIRECT LIGHTING - Lighting by luminaries 60 to 90% of their emitted light downward and the balance upward.
SEMI-INDIRECT LIGHTING - Lighting by luminaries 60 to 90% of their emitted light upward and the balance downward.
SHADE - Screen made of opaque or diffusing material designed to prevent alight source from being directly visible at normal angles of view.
SHEILDING ANGLE - Angle between horizontal line through the light center and the line of sight at which the bare source first becomes visible.
SKY FACTOR - Ratio of the illuminance on a horizontal plane inside a building dueto an unobstructed hemisphere of sky.  visit http://philarchreview.blogspot.com/
SKY LIGHT - Visible radiation from the sun redirected by the atmosphere.