Elec_Lighting Terms

SHEILDING ANGLE

Angle between horizontal line through the light center and the line of sight at which the bare source first becomes visible.

LOUVER SHIELDING ANGLE

Angle between the horizontal plane of baffles or louver grid and the plane at which the louver conceals all objects above.

ALTITUDE

Angular distance between the vertical plane containing the sun and the plane of the meridian.

FENESTRATION

Any opening or arrangement of openings (normally filled with media for control) for the admission of daylight.

COLD

CATHODE LAMP - Electric discharge lamp of the glow discharge type.

CEILING CAVITY

Cavity can formed by the ceiling, the plane of the luminaries, and the wall surfaces between these two planes.

ROOM CAVITY

Cavity formed by the plane of the luminaries, the work plane and the wall surfaces between these two planes.

FLOOR CAVITY

Cavity formed by the work plane, the floor, and the wall surfaces between these two planes.

LUMINOUS CEILING

Ceiling area lighting system comprising a continuous surface at diffuse transmitting material with light sources mounted above it.

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.

FILTER

Device for changing, by transmission, the magnitude and /or the spectral composition of the flux incident upon it.

DIFFUSER

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

REFLECTOR

Device used to redirect the luminous flux from a source by the process of reflection.

BALLAST

Device used with electric discharge lamp to obtain the necessary circuit conditions for starting and operating.

ACCENT LIGHT

Directional lighting to emphasize a particular object or draw attention to a part of the field of view.

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.

MERCURY LAMP

Electric discharge lamp in which the major portion of the radiation is produced by excitation of mercury atoms.

GASEOUS DISCHARGE

Emission of light from gas atoms excited by an electric current.

CHANNEL

Enclosure containing the ballast, starter, lamp holders, and wiring for a fluorescent lamp.

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.

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.

PREHEAT (Switch Start) FLOURESCENT LAMP

One designed for operation with a ballast that provides for preheating the electrodes in order to start the arc.

INSTANT START FLOURESCENT LAMP

One designed to start by high voltage without preheating of the electrodes.

REGRESSED LUMINAIRE

One mounted above the ceiling with the opening of the luminaire above ceiling line.

OVERCAST SKY

One that has 100% cloud cover; the sun is not visible.

PARTLY CLOUDY SKY

One that has 30 to 70% cloud cover.

CLERESTORY

Part of a building rising clear of the roofs and whose walls contain windows for lighting the interior.

MAINTENANCE FACTOR

Same as Light Loss Factor

SHADE

Screen made of opaque or diffusing material designed to prevent a light source from being directly visible at normal angles of view.

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.

LOUVER

Series of baffles used to shield a source from view at certain angles.

CLEAR SKY

Sky having less than 30% cloud cover.

LUX (lx)

The SI (metric) unit of illuminance . One lux is one lumen per sq.meter.

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.

ILLUMINANCE

The density of the luminous flux incident on a surface.

BRIGHTNESS

The terms Brightness and Luminance are almost entirely interchangeable, with the latter being the newer term (See Luminance)

LUMINOUS FLUX

The time rate of flow of light.

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.

LUMEN (LM)

The unit of luminous flux.

CANDELA

The unit of luminous intensity.

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.

SKY LIGHT

Visible radiation from the sun redirected by the atmosphere.

ELECTRIC DISCHARGE LAMP

Lamp in which light is produced by the passage of an electric current through a vapor or gas, as in fluorescent, cold-cathode, and mercury lamps.

DIFFUSE LIGHTING

Light that is not predominantly incident from any particular direction.

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.

GENERAL DIFFUSE LIGHTING

Lighting by luminaries distributing 40 to 60% of the emitted light downward and the balance upward and horizontally.

DIRECT LIGHTING

Lighting by luminaries distributing 90 to 100% of the emitted light in the direction (usually downward) of the surface to be illuminated.

INDIRECT LIGHTING

Lighting by luminaries distributing 90 to 100% of the omitted light upward.

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.

FLOURESCENT LAMP

Low- pressure mercury electric discharge lamp in which a fluorescing coating (phosphor) transforms some of the ultraviolet energy generated by the discharge into light.

BAFFLE

A single opaque or translucent element to shield a source from direct view at certain angles or to absorb unwanted Light.

LASER

Acronym for light amplification by stimulated emission of radiation. Highly monochromatic and coherent beam with a steady oscillation.

CEILING AREA LIGHTING

General lighting system in which the entire ceiling is, in effect, one large luminary, as in louvered ceilings and luminous ceilings.

ABSORPTION

General term for the process by which incident flux is dissipated.

DISCOMFORT GLARE

Glare producing discomfort but not necessarily impairing visual performance or visibility.

REFLECTED GLARE

Glare resulting from specular reflections of high luminance in polished or glossy surfaces in the field of view, especially within or in close proximity to the visual task.

DISSABILITY GLARE

Glare resulting in reduced visual performance and visibility.

DIRECT

INDIRECT LIGHTING - Variant of general diffuse lighting in which the luminaries emit little or no light at angles near the horizontal.

FLUSH MOUNTED OR RECESSED

Luminaire mounted above the ceiling with the opening of the luminaire flush with the surface of the ceiling.

CANDLE POWER

Luminous intensity expressed in candelas.

BLACK LIGHT

Popular term for ultraviolet energy near the visible spectrum.

ORIENTATION

Position of a building with respect to compass direction.

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.

DIFFUSE REFLECTION

Process by which the incident flux is redirected over a range of angles.

REFLECTION

Process by which the incident flux leaves a surface or medium from the incident side.

DIFFUSE TRANSMISSION

Process by which the incident flux passing through a surface or medium is scattered.

POLARIZATION

Process by which the transverse vibration of light waves are oriented in a specific plane.

FLOODLIGHT

Projector designed for lighting a scene or object to a luminance considerably greater than its surroundings.

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.

INFRARED RADIATION

Radiant energy within the wavelength range 770 to 10 to the 6 power nanometers.

LUMINAIRE EFFECIENCY

Ratio of luminous flux emitted by a luminaire to that emitted by the lamp or lamps used therein.

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.

DIFFUSE TRNSMITTANCE

Ratio of the diffusely transmitted flux leaving a surface or medium to the incident flux.

ABSORPTANCE

Ratio of the flux absorbed by a medium to the incident flux.

DIFFUSE REFLECTANCE

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

SKY FACTOR

Ratio of the illuminance on a horizontal plane inside a building due to an unobstructed hemisphere of sky.

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.

REFLECTANCE OF A SURFACE OR MEDIUM

Ratio of the reflected flux to the incident flux .

LAMP

Related term for a man-made source of light.

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.