Lamp qualities/
metrics
Seven key lamp metrics
The performance of a lamp can be measured in a number of ways, from the quantity of light
to the efficiency of the lamp itself.
Seven key lamp metrics
The performance of a lamp can be measured in a number of ways, from the quantity of light
to the efficiency of the lamp itself.
Light output
Seven key lamp metrics
The performance of a lamp can be measured in a number of ways, from the quantity of light
to the efficiency of the lamp itself.
Light output
Luminous intensity
Seven key lamp metrics
The performance of a lamp can be measured in a number of ways, from the quantity of light
to the efficiency of the lamp itself.
Light output
Luminous intensity
Illuminance
Seven key lamp metrics
The performance of a lamp can be measured in a number of ways, from the quantity of light
to the efficiency of the lamp itself.
Light output
Luminous intensity
Illuminance
Luminance
Seven key lamp metrics
The performance of a lamp can be measured in a number of ways, from the quantity of light
to the efficiency of the lamp itself.
Light output
Luminous intensity
Illuminance
Luminance
Efficacy
Seven key lamp metrics
The performance of a lamp can be measured in a number of ways, from the quantity of light
to the efficiency of the lamp itself.
Light output
Efficacy
Luminous intensity
Lumen maintenance
Illuminance
Luminance
Seven key lamp metrics
The performance of a lamp can be measured in a number of ways, from the quantity of light
to the efficiency of the lamp itself.
Light output
Efficacy
Luminous intensity
Lumen maintenance
Illuminance
Lamp life
Luminance
Light output (Lumen output)
Light output – also referred to as luminous flux –
quantifies the total light emitted in all directions.
Light output (Lumen output)
Light output – also referred to as luminous flux –
quantifies the total light emitted in all directions.
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Light output is measured in Lumens
Luminous intensity
Luminous intensity is the strength of light in a given direction.
Luminous intensity
Luminous intensity is the strength of light in a given direction.
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Luminous intensity is measured in Candelas
Luminous intensity
Luminous intensity is the strength of light in a given direction.
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Luminous intensity is measured in Candelas
As the name ‘Candelas’ suggests, its origin is in
19th century science when a standard candle was
defined as producing one candela in every direction.
This can be thought of as the power of light.
Illuminance (light level)
Lux measures the amount of light that falls on an
object or surface. It is therefore very important in
terms of designing a lighting system.
Illuminance (light level)
Lux measures the amount of light that falls on an
object or surface. It is therefore very important in
terms of designing a lighting system.
Lux = Lumens per sq. metre
Footcandles = Lumens per sq. ft
Illuminance (light level)
Lux measures the amount of light that falls on an
object or surface. It is therefore very important in
terms of designing a lighting system.
Lux = Lumens per sq. metre
Footcandles = Lumens per sq. ft
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Daylight illuminance (outdoor) Recommended illuminance in an operating theatre Overcast day illuminance (outdoor)
Typical illuminance in a general office
Typical illuminance in home
10,000 Lux
2,000 Lux
1,000 Lux
500 Lux
150 Lux
Luminance (perceived brightness)
Luminance refers to the ‘surface
brightness’ when looking in the direction
of the surface. In other words, this is
the human perception of brightness –
it is what we see!
Luminance (perceived brightness)
Luminance refers to the ‘surface
brightness’ when looking in the direction
of the surface. In other words, this is
the human perception of brightness –
it is what we see!
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Luminance is measured in candelas
per square metre (or per square foot).
The four measures of light
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Light output (Lumens)
The four measures of light
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Light output (Lumens)
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Luminous intensity (Candela)
The four measures of light
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Light output (Lumens)
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Luminous intensity (Candela)
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Illuminance (Lux/Footcandles)
The four measures of light
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Light output (Lumens)
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Luminance (Candela per m2/ft2)
Luminous intensity (Candela)
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Illuminance (Lux/Footcandles)
Efficacy (LPW)
This is a measurement of how effective the light source is
in converting electrical energy to lumens of visible light.
It is expressed in Lumens per Watt (LPW).
Efficacy (LPW)
This is a measurement of how effective the light source is
in converting electrical energy to lumens of visible light.
It is expressed in Lumens per Watt (LPW).
Average efficacy of lighting technologies (LPW)
Incandescent2-12
Halogen
5-22
CFL40-70
Metal Halide 65-110
HPS70-140
Fluorescent40-110
LED70-140
Lumen maintenance
Light output lessens over time.
How well a lamp maintains its light output over time
is an important measure of its performance.
Lumen maintenance
Light output lessens over time.
How well a lamp maintains its light output over time
is an important measure of its performance.
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Initial Lumens –
measured after 100 hours
Lumen maintenance
Light output lessens over time.
How well a lamp maintains its light output over time
is an important measure of its performance.
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Initial Lumens –
measured after 100 hours
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Mean Lumens –
describes lumen levels
at 40% of rated lamp
Lamp life
Rated lamp life is the length of time of a statistically
large sample between first use and the point when
50% of the lamps have failed.
Lamp life
Rated lamp life is the length of time of a statistically
large sample between first use and the point when
50% of the lamps have failed.
Average lamp life of lighting technologies (hours)
Incandescent 1,000-5,000
Halogen
2,000-5,000
CFL4,000-20,000
Metal Halide 6,000-24,000
HPS
12,000-55,000
Fluorescent
5,000-30,000
LED
10,000-50,000
Lamp life (LED)
The low failure rate of LED lamps requires
a different measure of ‘rated life’.
They will emit light for a very long time,
but the intensity will gradually deteriorate.
Lamp life (LED)
The low failure rate of LED lamps requires
a different measure of ‘rated life’.
They will emit light for a very long time,
but the intensity will gradually deteriorate.
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LED lamps are considered to have
a useful life until their light output
drops to 70% of initial lumen rating.
Lamp life (LED)
The low failure rate of LED lamps requires
a different measure of ‘rated life’.
They will emit light for a very long time,
but the intensity will gradually deteriorate.
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LED lamps are considered to have
a useful life until their light output
drops to 70% of initial lumen rating.
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The L70 rating of an LED lamp can be
50,000 hours or more.
Questions
?
What is ‘Lumen’ a measure of?
The efficacy of a lamp
Light output in a given direction
Total light output in all directions
The colour of light
What is ‘Lumen’ a measure of?
7 The efficacy of a lamp
7 Light output in a given direction
Total light output in all directions
7 The colour of light
What is luminance?
The amount of light falling on a surface
The direction of light from a given source
The light output from a given source
The perceived brightness of an object or surface
What is luminance?
7 The amount of light falling on a surface
7 The direction of light from a given source
7 The light output from a given source
The perceived brightness of an object or surface
What is illuminance measured in?
Lumens
Candelas
Lux/footcandles
Lumens per Watt
What is illuminance measured in?
7 Lumens
7 Candelas
Lux/footcandles
7 Lumens per Watt
The average efficacy of an LED lamp will be:
2-12 LPW
25-70 LPW
70-140 LPW
100-200 LPW
The average efficacy of an LED lamp will be:
7 2-12 LPW
7 25-70 LPW
70-140 LPW
7 100-200 LPW
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