LIGHTING TERMINOLOGY
JOB NAME
TI-51010
TYPE
GENERAL LIGHTING TERMS
CANDELA…the basic unit of luminous intensity
CANDLEPOWER…luminous intensity expressed in candelas.
LUMEN (LM)…the basic unit of measurement for light; also referred to as light flux. If a uniform point source of 1 candela is at the center of a sphere of 1-foot radius which
has an opening of 1 square foot at its surface, the quantity of light that passes through is called a lumen. The sphere has a total surface area of 12.57 square feet. Since,
by definition, a lumen flows to each square foot of a surface area, a uniform point of 1 candela produces 12.57 lumens.
FOOTCANDLE…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.
FOOTCANDLES = LUMENS PER SQUARE FOOT REACHING A SURFACE
1 footcandle = 1 lumen per square foot
1 footcandle = 10.76 Lux
LUX…the International System (SI) unit of illuminances when the meter is taken as the unit of length. It
is the illuminance on a surface one square meter in area on which there is uniformly distributed
flux of one lumen.
LUX = LUMENS PER SQUARE METER REACHING A SURFACE
1 Lux = 1 lumen per square meter
1 Lux = 0.0929 footcandles
LUMINANCE…or FOOTLAMBERT (FL) is a unit of luminance (photometric brightness) equal to
1/π candela per square foot, on the uniform luminance of a perfectly diffusing surface emitting or reflecting light at the rate of one lumen per square foot, or to the average
luminance of any surface emitting or reflecting light at that rate. The average luminance of any reflecting surface in footlamberts is:
FL = FOOTCANDLES X SURFACE REFLECTANCE
NADIR…is a point directly below a luminaire (the zero degree line of candela distribution curves)
CUTOFF ANGLE (OF A LUMINAIRE)…is the angle, measured up from nadir, between the vertical axis and the first line of sight at which the bare source is not visible
FLOODLIGHT PHOTOMETRICS:
FLOODLIGHT PHOTOMETRICS:
“Field vs. Beam”
“Field vs. Beam”
SHIELDING ANGLE (OF A LUMINAIRE)…is the angle between a horizontal line through the light center and the line of sight at which the bare source first becomes visible
CUTOFF ANGLE
Beam Angle…
is the number of
degrees
in...is
thethe
Beam
Angle
number
of degrees
horizontal
and in
the horizontal and
vertical
planes
vertical
planes
at at
which 50% of the
which 50% of the
maximum
candlepower
occurs.
maximum candlepower occurs.
SHIELDING ANGLE
Maximum
Candlepower
Angle used to
determine “NEMA”
zone size
Field Angle
(formerly beam
spread)…is the
number of degrees
in the horizontal
and
vertical
Field
Angleplanes
(formerly
spread)...is
atbeam
which
10% of the
number of degrees in
the maximum
horizontal and
the
vertical planes at
candlepower
which 10% of the
maximum candleoccurs.
power occurs.
QUANTITY OF LIGHT
The basic measure of illuminance is the footcandle. One footcandle is equal to one
unit of light flux (one lumen) distributed evenly over a one-square foot of surface area.
Several different footcandle measures are considered for outdoor lighting.
ILLUMINANCE:
The preferred term for the density of luminous flux (lumens)
falling on a surface. Illuminance is measured in either Footcandles or Lux
(metric). It is the quotient of that light divided by the area of the surface if
it is uniformly illuminated.
HORIZONTAL FOOTCANDLES:
The footcandles falling on a horizontal surface. All horizontal footcandles
are in the same plane for the same surface. They can be added together
arithmetically when more than one source provides light to the same
surface.
© 2013 Koninklijke Philips Electronics N.V. All rights reserved.
Specifications are subject to change without notice.
www.philips.com/luminaires
TI-51010 03/13 VERTICAL FOOTCANDLES:
The footcandles falling on a vertical surface, such as a wall. Vertical
footcandles may not all be in the same plane; depending on the direction
of light rays, vertical footcandles from different sources may not be
additive.
FOOTCANDLE (or uniformity) RATIO:
The ratio between average footcandles and minimum footcandles (such as
3:1) or maximum and minimum footcandles (such as 6:1). The maximum/
minimum ratio generally is preferred. (The lower the ratio, the more
uniform is the lighting). We don’t see footcandles…only the footlamberts
they produce.
LIGHTING TERMINOLOGY
INITIAL FOOTCANDLES:
The footcandles (minimum, maximum, or average) produced when luminaires
and lamps are new.
MAINTAINED FOOTCANDLES:
The footcandles (minimum, maximum, or average) calculated through
application of a light loss factor, which takes into account such factors as lamp
lumen depreciation, dirt depreciation, ballast factor, etc.
MINIMUM FOOTCANDLES:
The least amount of light (illuminance) falling on that point of a surface or
anywhere on the area being lighted.
MAXIMUM FOOTCANDLES:
The maximum amount of light falling on that point of a surface or anywhere on the
area being lighted.
AVERAGE FOOTCANDLES:
The theoretical average amount of light falling on a surface when averaging the
illuminance falling on all points of the surface.
ENERGY GLOSSARY OF TERMS
WATT (W)…is the unit to measure power consumption.
KILOWATT (kW)…is a larger unit of power; a thousand watts (watts x 1000 =
kilowatts)
KILOWATT HOUR (kWh)…is the measure of electrical consumption from which
electricity billing is determined. For example, a 1000-watt lamp operated for
100 hours would consume 100 kilowatt hours, (1000 watts x 100 hours = 100
kWh). At a billing rate of $0.10/kWh, this lamp would cost $10.00 (100 kWh x
$0.10/kWh) to operate.
QUALITY OF LIGHT
Pertains to distribution of luminance in an environment. It is a positive term that implies
that all lighting should contribute favorably to visual performance, comfort, ease of seeing,
safety and aesthetics. It is usually regarded as the absence of harshness, glare or other
discomfort factors.
BRIGHTNESS…is a subjective (usually negative) psychological reaction to lighting.
Brightness is sometimes referred to with statements such as “the brighter the
bulb, the better.” This is inaccurate. “Brightness” does not refer to the amount
of light coming from a given light source, but rather to the way your eye
perceives that light. For example, brightness is used in reference to the effect
on your eyes from the headlights of an approaching car and your reaction to
them.
GLARE…is the sensation produced by luminance within the visual field that is
significantly greater than the illuminance to which the eyes are adapted. It
results from high luminances or insufficiently shielded light sources in the field
of view or from reflecting areas of high luminance.
DISABILITY GLARE…results in reduced visual performance and visibility. It often is
accompanied by discomfort.
DISCOMFORT GLARE…is glare producing discomfort. It does not necessarily
interfere with visual performance or visibility.
LIGHT TRESPASS…is a situation which occurs when, due to lack of adequate beam
control, light from a source is distributed onto areas where the illumination is
unwanted.
SPILL LIGHT…lumens distributed by the luminaire which are outside the beam
spread.
© 2013 Koninklijke Philips Electronics N.V. All rights reserved.
Specifications are subject to change without notice.
www.philips.com/luminaires
TI-51010 03/13 TI-51010
LIGHTING EFFICIENCY
The term efficiency indicates how much energy is needed to perform a given function.
Several types of efficiencies are considered in outdoor lighting:
LUMINOUS EFFICACY OF A SOURCE OF LIGHT:
A measure of efficiency (efficacy) of a lamp output (lumens) to the power
consumed (watts) expressed in lumens per watt.
EFFICIENCY:
Common usage refers to the term light source efficiency even today in
terms of lumens per watt. However, it may be also used in reference to
the efficiency of a luminaire or fixture. In this case it may be the ratio
(percentage) of lumens emitted by the fixture as compared to the
lumens emitted by the lamp or lamps within the fixture.
COEFFICIENT OF UTILIZATION (CU):
It is simply a measure of efficiency of the delivery of light from a luminaire
into a given area. The ratio (percentage) of the light or lumens from
a luminaire that are received on the area as compared to the
total number of lumens emitted by the lamps alone. Ex., if the lamp
produces 50,000 lumens and 20,000 lumens reach the area to be illuminated,
the coefficient of utilization is 40% (20,000/50,000).
COEFFICIENT OF BEAM UTILIZATION (CBU):
The percentage of beam flux (lumens) within the beam spread
reaching the area to be illuminated. Ex., if the beam spread contains
30,000 beam flux (lumens) and 25,000 beam flux (lumens) reach the area to be
illuminated, the coefficient of beam utilization is 83% (25,000/30,000).
MAINTENANCE FACTORS (CAUSING DECLINING
ILLUMINANCE)
LAMP LUMEN DEPRECIATION (LLD):
A factor used in lighting calculations to account for the light loss of a specific
lamp that takes place due to the gradual decay in lumen output over a
designated period of burning time.
LUMINAIRE DIRT DEPRECIATION (LDD):
The multiplier used to account for the accumulation of dirt on luminaires
resulting in loss in light out­put to the time of cleaning or relamping. Luminaires
have six maintenance categories, depending on five degrees of dirt conditions:
• Very clean
• Clean
• Medium
• Dirty
• Very dirty
BALLAST FACTOR (BF):
The lamp output on a commercial ballast compared to the lamp output on a
reference ballast.
LIGHT LOSS FACTOR (LLF):
The product of the:
• Lamp Lumen Depreciation (LLD)
• Luminaire Dirt Depreciation (LLD)
• Ballast Factor (BF)
LLF = LLD x LDD x BF
LIGHTING TERMINOLOGY
TI-51010
TILT ANGLE: (Metal Halide Lamps)
Operating metal halide lamps designated as base up or base down at
angles away from vertical can significantly decrease initial lumen output.
This decrease in output must be considered in design computations when
a position other than vertical is used such as in floodlighting luminaires.
Operating lamps at angles away from vertical can also adversely affect
lamp life.
LIGHT SOURCES
ELECTRIC-DISCHARGE LAMP…is 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.
Note: Electric-discharge lamps may be named after the filling gas or
vapor that is responsible for the major portion of the radiation; e.g.,
mercury lamps, sodium lamps, neon lamps, argon lamps, etc. A second
method of designating the electric-discharge lamps is by the physical
dimensions or operating parameters; e.g., short-arc lamps, high pressure
lamps, low pressure lamps, etc.
Typical Metal Halide Lamp Tilt Factors
Operating Angle from Vertical
0°
5°
10°
15°
20°
25°
30°
35°
40°
45°
50°
55°
60°
65°
70°
75°
80°
85°
90°
Percent of Initial Lumens
400 Watt
1000 Watt
1500 Watt
Operating Angle
from Horizontal
100
98.3
96.7
95
94.7
94.3
94
92.7
91.3
90
89.3
88.7
88
87.7
87.3
87
89.3
91.7
94
100
98.3
96.7
95
94.7
94.3
94
92.7
91.3
90
89.3
88.7
88
87.7
87.3
87
89.3
91.7
98
100
98.3
96.7
95
94.7
94.3
94
93.7
93.3
93
91.3
89.7
88
87.7
87.3
87
90.3
93.7
97
90°
85°
80°
75°
70°
65°
60°
55°
50°
45°
40°
35°
30°
25°
20°
15°
10°
5°
0°
These lamps have become popular primarily for three reasons:
1. High efficacy–more lumens per watt of electricity consumed
2. Long lamp life and good lumen maintenance–reduces operating expenses
3. Compact source–permits good light control by use of reflectors and refractors, resulting in higher efficiency.
HIGH INTENSITY DISCHARGE LAMPS…a general grouping of lamps consisting of high pressure sodium, mercury, and metal halide lamps.
HIGH PRESSURE SODIUM LAMP…is a high intensity discharge lamp producing light primarily by the radiation from sodium vapors at relatively high pressures. Included are
clear and diffuse-coated types. They offer more lumens per watt than Mercury or Metal Halide sources as well as long life. They emit a golden white color compared to
whiter light sources, i.e., Metal halide. Energy savings is one advantage with HPS systems. HPS gives a yellow/orange tint to a white surface, accents yellow and orange, and
tends to gray deep reds, greens and blues.
Advantages
• Long lamp life (24,000 hrs)
• Exceptionally high efficacy
(lumens per watt)
• Lowest operating cost
Disadvantages
• High initial cost
• Doesn’t restart immediately after power
• failure with normal auxiliary equipment, but
• restarts quicker than mercury and metal halide
• (1 minute)
• Fair color rendition
MERCURY LAMP…is a high intensity discharge light source producing light by radiation from mercury vapor under pressure. Included are clear, phosphor-coated (mercuryfluorescent), and self-ballasted types. It was the first HID lamp developed. Their advantage is that they offer long life. Their disadvantages are poor color rendition and low
efficacy. Clear Mercury gives a slight blueish green tint to a white surface, accents red, yellow, blue and green, and tends to gray deep reds.
Advantages
Disadvantages
• Long lamp life (16,000-24,000 hrs or • more) compared to incandescent
• High light output (lumens per watt)
• Low operating cost
• High initial cost
• Large light source
• Limited beam control especially with phosphor coated lamps
• Low efficacy compared to MH and HPS
• Poor color rendition
• Does not start immediately after power failure,
but quicker than metal halide (3-6 minutes)
•
METAL HALIDE LAMP...is a high intensity discharge lamp producing light by radiation from mercury, together with halides of metals such as sodium and scandium. Included are
clear and phosphor-coated types. Their lumen output per watt is almost double that of Mercury lamps. They are used in installations that require good efficacy, color and
light control. Lamp life is approximately half that of Mercury lamps. Metal Halide gives a slight blue to a white surface, accents yellow, green and blue, and tends to gray reds.
Advantages
Disadvantages
• Moderately long lamp life (7,500-20,000 hrs)
• Higher light output than mercury
for a given wattage
• Good color rendition, makes colors look
• close to natural
• Good beam control
• Low operating cost
• Higher initial cost
• Does not restart immediately after power
© 2013 Koninklijke Philips Electronics N.V. All rights reserved.
Specifications are subject to change without notice.
www.philips.com/luminaires
TI-51010 03/13 • failure
• Slowest to restrike (10-15 minutes)
LIGHTING TERMINOLOGY
TI-51010
HALOGEN LAMP (TUNGSTEN-HALOGEN LAMP–QUARTZ)…is an incandescent lamp containing a halogen gas which recycles tungsten (which would ordinarily be
deposited on the bulb wall) back onto the filament surface.
Advantages
Disadvantages
• Makes colors look natural
• Good lumen maintenance (light
output remains almost the same
• throughout life)
• Low light output (lumens per watt)
• Elongated source limits beam control
• Medium lamp life (2,000-4,000 hours)
• High operating cost
AVERAGE RATED LIFE…references the life of the lamp. The hour rating is the point in time when 50 percent of the tested samples have burned out and 50 percent are still
operating.
HID WARMUP CHARACTERISTICS...time for lamp to reach 80% light output
High Pressure Sodium
Metal Halide
Pulse Start MH
3-4 minutes
2-4 minutes
1-2 minutes
HID RESTRIKE CHARACTERISTICS...All HID lamps will deionize when there is a power interruption or if voltage at the lamp socket drops below the amount required to
sustain the arc for more than a few cycles. Because it takes a greater voltage to ionize the arc tube vapors while they are hot and under higher pressure, the lamp will not
re-start immediately.
TIME TO RESTRIKE (when hot)
High Pressure Sodium
Metal Halide
Pulse Start MH
1-3 minutes
10-15 minutes
4-6 minutes
STROBOSCOPIC EFFECT...HID lamp output tends to follow the alternating current waveform. This can cause small moving objects to flicker or appear motionless. To avoid
this annoyance, three phase power is suggested for high pressure sodium and mercury lamps. Split phase ballasting can also be used with mercury lamps. Single phase power
can be used with metal halide lamps.
© 2013 Koninklijke Philips Electronics N.V. All rights reserved.
Specifications are subject to change without notice.
www.philips.com/luminaires
TI-51010 03/13 Philips Lighting Company
200 Franklin Square Drive
Somerset, NJ 08873
Phone: 855-486-2216
Philips Lighting Company
281 Hillmount Road
Markham ON, Canada L6C 2S3
Phone: 800-668-9008