| Candlepower Distribution Curve |
A curve, generally polar, representing the variation
of luminous intensity of a lamp or luminaire in a plane through
the light center. |
| Cavity Ratio |
A number indicating cavity proportions calculated
from length, width and height. |
| Class "P" Ballast |
Contains a thermal protective device which
deactivates the ballast when the case reaches a certain critical
temperature. The device resets automatically when the case temperature
drops to a lower temperature. |
| Coefficient of Utilization (CU) |
The ratio of the luminous flux (lumens) from
a luminaire calculated as received on the work-plane to the
luminous flux emitted by the luminaires lamps alone. |
| Cold Cathode Lamp |
An electric-discharge lamp whose mode of operation
is that of a flow discharge. |
| Colorimetry |
The measurement of color. |
| Color Rendering Index (CRI) |
Measure of the degree of color shift objects
undergo when illuminated by the light source as compared with
the color of those same objects when illuminated by a reference
source of comparable color temperature. |
| Color Temperature |
The absolute temperature of a blackbody radiator
having a chromaticity equal to that of the light source. |
| Cone Reflector |
Parabolic reflector that directs light downward
thereby eliminating brightness at high angles. |
| Contrast |
The difference in brightness (luminance) of
an object and its background. |
| Cool Beam Lamps |
Incandescent PAR lamps that use a special coating
(dichroic interference filter) on the reflectorized potion of
the bulb to allow heat to pass out the back while reflecting
only visible energy to the task, thereby providing a "cool
beam" of light. |
| Cove Lighting |
Lighting comprising sources sheilded by a ledge
or horizontal recess, and distributing light over the ceiling
and upper wall. |
| Cutoff Luminaires |
Outdoor luminaires that restrict all light
output to below 85° from vertical.
 |
| Digital Addressable Lighting
Interface (DALI) |
An open communications protocol used by multiple
control and ballast manufacturers for digital control. |
| Dimming Ballast |
Special fluorescent lamp ballast, which when
used with a dimmer control, permits varying light output. |
| Direct Current (DC) |
Flow of electricity continuously in one direction
from positive to negative. |
| Direct Lighting |
Lighting involving luminaires that distribute
90 to 100% of emmited light in the general direction of the
surface to be illuminated. The term usually refers to light
emitted in a downward direction. |
| Direct Glare |
Glare resulting from high luminances or insufficiently
shielded light sources in the field of view. It usually is associated
with bright areas, such as luminaires, ceilings and windows
which are outside the visual tasks or region being viewed. |
| 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 a gas. |
| Discomfort Glare |
Glare producing discomfort. It does not necessarily
interfere with visual performance or visibility. |
| Downlight |
A small direct lighting unit which directs the light downward.
|
| Emergency Lighting
|
Lighting system designed to provide minimum
illumination required for safety, during power failures. |
| Efficacy |
See Lamp Efficacy. |
| Efficiency |
See Luminaire Efficiency |
| Equivalent Sphere Illumination (ESI)
|
The level of sphere illumination which would
produce task visibility equivalent to that produced by a specific
lighting environment. |
| "ER" (Elliptical Reflector)
|
Lamp whose reflector focuses the light about
2" ahead of the bulb, reducing light loss when used in
deep baffle downlights. |
| Extended Life Lamps |
Incandescent lamps that have an average rated
life of 2500 or more hours and reduced light output compared
to standard general service lamps of the same wattage.
|
| Fill Light |
Illumination added to reduce shadows or contrast
range. |
| Fixture |
Another name for a luminaire. |
| Floodlighting |
A system designed for lighting a scene or object
to a luminance greater than its surroundings. It may be for
utility, advertising or decorative purposes. |
| Fluorescent Lamp |
A low-pressure mercury electric-discharge lamp
in which a phosphor coating transforms some of the ultraviolet
energy generated by the discharge into light. |
| Footcandle (fc) |
The unit of illuminance when the foot is taken
as the unit of length. It is the illuminance on a surface one
square foot in area on which there is a uniformly distributed
flux of one lumen. |
| Foot Lambert (fl) |
A unit of luminance of perfectly diffusing
surface emitting or reflecting light at the rate of one lumen
per square foot. |
| Footlights |
A set of striplights at the front edge of the
stage plateform used to soften face shadows cast by overhead
luminaires and to add general toning lighting from below.
|
| General Lighting |
See Ambient Lighting. |
| General Service Lamps |
"A" or "PS" incandescent
lamps. |
| Glare |
The sensation produced by luminance within
the visual field that is sufficiently greater than the luminance
to which the eyes are adapted to cause annoyance, discomfort,
or loss in visual performance and visibility. |
| Ground Relamping |
Relamping of a group of luminaires at one time
or reduce relamping labor costs.
|
| High Intensity Discharge
(HID) Lamp |
A discharge lamp in which the light producing
arc is stabilized by wall temperature, and the arc tube has
a bulb wall loading in excess of three watts per square centimeter.
HID lamps include groups of lamps known as mercury, metal halide,
and high pressure sodium. |
| High Output Fluorescent Lamp |
Operates at 800 or more milliamperes for higher
light output than standard fluorescent lamp (430MA). |
| High Pressure Sodium (HPS) Lamp |
High intensity discharge (HID) lamp in which
light is produced by radiation from sodium vapor. Includes clear
and diffuse-coated lamps.
|
| Incandescence |
The self-emission of radiant energy in the
visible spectrum due to the thermal excitation of atoms or molecules.
|
| Incandescent Lamp |
A lamp in which light is produced by a filament
heated to incandescence by an electric current. |
| Instant Start Fluorescent Lamp |
A fluorescent lamp designed for starting by
a high voltage without preheating of the electrodes. |
| Inverse Square Law |
The law stating that the illuminance at a point
on a surface varies directly with the intensity of a point source,
and inversely as the square of the distance between the source
and the point. If the surface at the point is normal to the
direction of the incident light, the law is expressed by fc=cp/d2.
|
| Kelvin |
Unit of measurement for color temperature.
The Kelvin scale starts from absolute zero, which is -273° Celsius.
|
| Kilowatt-Hour (KWH) |
Unit of electrical power consumed over a period
of time. KWH = watts/1000 x hours used.
|
| Lamp |
An artificial source of light (also portable
luminaire equipped with a cord and plug). |
| Lamp Efficacy |
The ratio of lumens produced by a lamp to the
watts consumed. Expressed as lumens per watt (LPW). |
| Lamp Lumen Depreciation (LLD) |
Multiplier factor in illumination calculations
for reduction in the light output of a lamp over a period of
time. |
| Light |
Radiant energy that is capable of exciting
the retina and producing a visual sensation. The visible portion
of the electromagnetic spectrum extends from about 380 to 770
nm. |
| Lens |
Used in luminaires to redirect light into useful
zones. |
| Local Lighting |
Lighting designed to provide illuminance over
a relatively small area or confined space without providing
any significant general surrounding lighting. |
| Louver |
A series of baffles used to shield a source
from view at certain angles or to absorb unwanted light. The
baffles usually are arranged in a geometric pattern. |
| Long Life Lamps |
See Extended Life Lamps. |
| Low Pressure Sodium Lamp |
A discharge lamp in which light is produced
by radiation of sodium vapor at low pressure producing a single
wavelength of visible energy, i.e. yellow. |
| Low Voltage Lamps |
Incandescent lamps that operate at 6 to 12
volts. |
| Lumen |
The unit of luminous flux. It is the luminous
flux emitted within a unit solid angle (one steradian) by a
point source having a uniform luminous intensity of one candela.
|
| Luminaire |
A 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 Direct Depreciation (LDD)
|
The multiplier to be used in illuminance provided
by clean, new luminaires to the reduced illuminance that they
will provide due to direct collection on the luminaires at the
time at which it is anticipated that cleaning procedures will
be instituted. |
| Luminaire Efficiency |
The ratio of luminous flux (lumens) emitted
by a luminaire to that emitted by the lamp or lamps used. |
| Luminance |
The amount of light reflected or transmitted
by an object. |
| Lux |
The metric unit of illuminance. One lux is
one lumen per square meter (lm/m2).
|
| Maintenance Factor (MF)
|
A factor used in calculating illuminance after
a given period of time and under given conditions. It takes
into account temperature and voltage variations, dirt accumulation
on luminaire and room surfaces, lamp depreciation, maintenance
procedures and atmosphere conditions.
|
| Mercury Lamp |
A high intensity discharge (HID) lamp in which
the major portion of the light is produced by radiation from
mercury. Includes, clear, phosphor-coated and self-ballasted
lamps. |
| Metal Halide Lamp |
A high intensity discharge (HID) lamp in which
the major portion of the light is produced by radiation of metal
halides and their products of dissociation-possible in combination
with metallic vapors such as mercury. Includes clear and phosphor
coated lamps.
|
| Nadir |
Vertically downward directly below the luminaire
or lamp; designated as 0°. |
| Overall Length (OAL)
|
Maximum overall length of a light fixture.
|
| "PAR" Lamps
|
Parabolic aluminized reflector lamps which
offer excellent beam control, come in a variety of beam patterns
from very narrow spot to wide flood and can be used outdoors
unprotected because they are made of "hard" glass
that can withstand adverse weather. |
Parabolic Louvers |
A grid of baffles which redirect light downward
and provide very low luminaire brightness. |
| Photometry |
The measurement of light quantities. |
| Point Method Lighting Calculation |
A lighting design procedure for predetermining
the illuminance at various locations in lighting installations,
by use of luminaire photometric data. |
| Polarization |
The process by which the transverse vibrations
of light waves are oriented in a specific plane. Polarization
may be obtained by using either transmitting or reflecting media.
|
| Power Factor |
Ratio of: Watts (volts x amperes) Power factor
in lighting is primarily applicable to ballasts. Since volts
and watts are usually fixed, amperes (or current) will go up
as power factor goes down. This necessitates the use of larger
wire sizes to carry the increased amount of current needed with
Lowe Power Factor (L.P.F) ballasts. The addition of a capacitor
to an L.P.F. ballast converts it to a H.P.F. ballast. |
| Preheat Fluorescent Lamp |
A fluorescent lamp designed for operation in
a circuit requiring a manual or automatic starting switch to
preheat the electrode in order to start the arc.
|
| "R" Lamps
|
Reflectorized lamps available in spot (clear
face) and flood (frosted face). |
| Rapid Start Fluorescent Lamp |
A fluorescent lamp designed for operation with
a ballast that provides a low-voltage winding for preheating
the electrodes and initiating the arc without a starting switch
or the application of high voltage. |
| Raw Footcandles |
See Footcandles. |
| Reflection |
Light bouncing off a surface. In specular reflection
the light strikes and leaves a surface at the same angle. Diffuse
reflected light leaves a surface in all directions. |
| Reflectance |
Sometimes called reflectance factor. The ratio
of reflected light to incident light (light falling on a surface).
Reflectance is generally expressed in percent. |
| Reflected Glare |
Glare resulting from specular reflections of
high luminances in polished or glossy surfaces in the field
of view. It usually is associated with reflections from within
a visual task or areas in close proximity to the region being
viewed. |
| Reflector |
A device used to redirect the light flow from
a source by bouncing it off the surface. |
| Refraction |
The 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. |
| Room Cavity Ration (RCR) |
A number indicating room cavity proportions
calculated from length, width and height. |
| Rough Service Lamps |
Incandescent lamps designed with extra filament
supports to withstand bumps, shocks and vibrations with some
loss in lumen output.
|
| Self-ballasted Mercury Lamps
|
Any mercury lamp of which the current-limiting
device is an integral part. |
| Silver Bowl Lamps |
Incandescent "A" lamps with a silver
finish inside the bowl or portion of the bulb. Used for indirect
lighting. |
| Spacing Ratio |
Ratio of the distance between luminaire centers
to the mounting height above the work-plane for uniform illumination.
|
| Spectral Energy Distribution (SED) Curves
|
A plot of the level of energy at each wavelength
of a light source. |
| Spectral Power Distribution (SPD) |
The output of a light source can be characterized
by its relative power at each wavelength. The output is measured
and is placed on a graph which shows power vs. wavelength, which
then shows which wavelengths a particular light source is stronger
or weaker in possessing. |
| Sphere Illumination |
The illumination on a task from a source providing
equal luminance in all directions about that task, such as an
illuminated sphere with the task located at the center. |
| Surface Mounted Luminaire |
A luminaire that is mounted directly on a ceiling. |
| Suspended (Pendant) Luminaire |
A luminaire that is hung from a ceiling by
supports.
|
| Task Lighting |
Lighting directed to a specific surface or area
that provides illumination for visual tasks. |
| Three-Way Lamps |
Incandescent lamps that have two separately switched
filaments permitting a choice of three levels or light such
as 30/70/100, 50/100/150 or 100/200/300 watts. They can only
be used in a base down position. |
| Transformer |
A device to raise or lower electric voltage. |
| Transmission |
The passage of light through a material. |
| Tungsten-Halogen Lamp |
A gas filled tungsten incandescent lamp containing
a certain proportion of halogens.
|
| Veiling Reflections |
Regular reflections superimposed upon diffuse
reflections from an object that partially or totally obscure
the details to be seen by reducing the contrast. This is sometimes
called reflected glare. |
| Vibration Service Lamps |
See Rough Service Lamps. |
| Visual Comfort Probability (VCP) |
The rating of a lighting system expressed as a
percent of people who, when viewing from the specified location
and in a specified direction, will be expected to find it acceptable
in terms of discomfort glare. |
| Visual Edge |
The line on a isolux chart which has a value equal
to 10% of the maximum illumination. |
| Visual Field |
The field of view that can be perceived when the
head and eyes are kept fixed.
|
| Wall Wash Lighting |
A smooth even distribution of light over a wall. |
| Watt (W) |
The unit for measuring electric power. It defines
the power or energy consumed by an electrical device. The cost
of operating an electrical device is determined by the watts
it consumes times the hours or use. It is related to volts and
amps by the following formula: Watts = Volts x Amps. |
| Zonal Cavity Method Lighting
Calculation |
A lighting design procedure used for predetermining
the relation between the number and types of lamps or luminaires,
the room characteristics, and the average illuminance on the
work-plane. It takes into account both direct and reflected
flux.
|
Lighting Glossary