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ILLUMINATION
TERMINOLOGY IN ILLUMINATION, DEFINITIONS, UNITS
LUMINANCE (L):
•Amount of light emitted from an object in a given direction. The eye
can see objects because these send light to the eye.
•Luminance is a photometric measure of the luminous intensity per unit
area of light travelling in a given direction.
•The luminance indicates how much luminous power will be detected by
an eye looking at the surface from a particular angle of view. Luminance
is thus an indicator of how bright the surface will appear.
•It is measured in candelas per sq.m. (cd/m²) – SI unit.
•A typical computer display emits between 50 and 300 cd/m2. The sun
has luminance of about 1.6×109 cd/m2 at noon.
ILLUMINATION
TERMINOLOGY IN ILLUMINATION, DEFINITIONS, UNITS
ILLUMINANCE (E):
•Illuminance on a surface is the amount of light incident on that surface.
•It is the ratio of the quantity of light falling on a surface and the area
that is illuminated.
•illuminance is the total luminous flux incident on a surface, per unit
area. It is a measure of how much the incident light illuminates the
surface.
• SI unit - lux or lumen/m² .
•Non metric unit of illuminance is foot-candle.
LUX METER FOR MEASURING ILLUMINANCE IN
WORKING ENVIRONMENT
ILLUMINATION
TERMINOLOGY IN ILLUMINATION, DEFINITIONS, UNITS
AMPERES:
•Measurement of current flow is ampere.
•Amp. rating is marked on many electric products & special purpose
lights to ensure adequate wiring for the application.
LUX:
•1 lux is equal to the illuminance provided by an ordinary wax candle on
a spherical surface with an area equal to 1 sq.m., from 1 m away.
• Measure of luminous flux spread over a given area – luminous flux
(measured in lumens) is a measure of the total amount of visible light
present.
•A flux of 1,000 lumens, concentrated into an area of one square metre,
lights up that square metre with an illuminance of 1,000 lux. However,
the same 1,000 lumens, spread out over ten square metres, produces a
dimmer illuminance of only 100 lux.
•1 lux = 0.0929 footcandles.
ILLUMINATION
TERMINOLOGY IN ILLUMINATION, DEFINITIONS, UNITS
LUMEN:
•The lumen (symbol: lm) is the SI unit of luminous flux, a measure of the
total amount of visible light emitted by a source.
CANDELA:
•The candela (symbol: cd) is the SI unit of luminous intensity; that is,
power emitted by a light source in a particular direction.
• A common candle emits light with a luminous intensity of roughly one
candela.
•If emission in some directions is blocked by an opaque barrier, the
emission would still be approximately one candela in the directions that
are not blocked.
ILLUMINATION
TERMINOLOGY IN ILLUMINATION, DEFINITIONS, UNITS:
FOOT CANDLE (lumen/sq.ft.):
•A foot-candle (abbreviated as fc) is a non-SI unit of illuminance or light
intensity .
• The name "footcandle" conveys “the illuminance cast on a surface by a
one-candela source one foot away.”
•The unit is defined as the amount of illumination the inside surface of a
1-foot radius sphere would be receiving if there were a uniform point
source of one candela in the exact center of the sphere.
1 foot-candle = 1 lumen per square foot.
1 foot candle = 10.764 lux
EFFICACY:
•Luminous efficacy is a measure of how well a light source produces
visible light - measure of the efficiency with which the source provides
visible light from electricity.
•The efficiency of a lamp measured in ratio of lumens per watt (LPW) –
more lumens per watt more efficient the lamp.
•A higher LPW means the bulb converts power into light in a more
efficient manner.
EFFICIENCY:
•Light output from a luminaire (fixture) as a % of light output from the
bulb it uses.
•For instance, a fixture with a fluorescent bulb that emits 1000 lumens
may have a shade/cover that decreases the direct light emitted to only
900 lumens. That fixture would be considered 90% efficient.
SI PHOTOMETRY UNITS:
Quantity SI unit Symbol
Luminous flux lumen lm
Luminous intensity Candela cd
Luminance Candelas per sq.m. cd/m²
Illuminance Lux (lumen per sq.m.) lx
Luminous efficacy Lumen per watt lm/watt LPW
*Luminous flux/luminous power is the measure of the power of light / the measure of
the total power of light emitted.
LUMINAIRES:
•Lighting industry uses this term to indicate ‘lighting fixtures or ‘fittings’.
•Luminaires are grouped by mounting type & locations:
Ceiling mounted Wall-mounted Architectural
Suspended Furniture/cabinet integrated
Recessed Plug-in Exterior luminaire
GLARE
•Glare is difficulty seeing in the presence of bright light such as direct or
reflected sunlight or artificial light such as car headlamps at night.
•Glare is an interference with visual perception caused by an
uncomfortably bright light source or reflection; a form of visual noise.
a) Direct glare
b) Indirect glare / Reflected glare
c) Discomfort glare
d) Disability glare
e) Blinding glare
DIRECT GLARE
•Bare bulb glare - eliminate by:
 changing a shade
adjusting angle of a fixture
Replacing bulb with one of a lower wattage
Replacing bulb – from clear to frosted – from thinly frosted to
thickly frosted.
*if necessary add another light source on the ceiling or wall.
•In recessed lighting baffles can absorb unwanted light or shield the light
source from direct view.
•With new furniture layout reassess for glare. For e.g., re-orienting a
family room sofa to face a game table might cause those seated on the
sofa to look directly up into the exposed bulbs of a suspended pendant
fixture.
INDIRECT GLARE
•Any flat reflective surface can be the source of indirect glare. E.g., shiny
desktops, countertops, tables, mirrors, computer screens, glass over
pictures, television screen, even enameled or metallic surfaces, window
glass.
•As obvious as direct glare , reflected / indirect glare can cause eye-
strain.
•To solve reflected glare problem:
Shift light sources
Shift furniture
GLARE
Glare can be divided into following types (depending on magnitude):
•Discomfort glare (less severe case): distracting or uncomfortable,
which interferes with the perception of visual information required to satisfy
biological needs, but which does not significantly reduce the ability to see
information needed for activities.
•Disability glare (severe situation): renders the task impossible to view -
reduces the ability to perceive the visual information needed for a particular
activity - such as when driving westward at sunset.
•Blinding Glare: so intense that for an appreciable length of time after it has
been removed, no visual perception is possible.
 Direct glare - glare of a truck light or exposed bulb. Victims of indirect glare
may not know the source, but experience headaches, eye strain & general
discomfort.
A good lighting plan should eliminate direct & indirect glare.

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Lighting architecture lecture 3

  • 1. ILLUMINATION TERMINOLOGY IN ILLUMINATION, DEFINITIONS, UNITS LUMINANCE (L): •Amount of light emitted from an object in a given direction. The eye can see objects because these send light to the eye. •Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. •The luminance indicates how much luminous power will be detected by an eye looking at the surface from a particular angle of view. Luminance is thus an indicator of how bright the surface will appear. •It is measured in candelas per sq.m. (cd/m²) – SI unit. •A typical computer display emits between 50 and 300 cd/m2. The sun has luminance of about 1.6×109 cd/m2 at noon.
  • 2. ILLUMINATION TERMINOLOGY IN ILLUMINATION, DEFINITIONS, UNITS ILLUMINANCE (E): •Illuminance on a surface is the amount of light incident on that surface. •It is the ratio of the quantity of light falling on a surface and the area that is illuminated. •illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates the surface. • SI unit - lux or lumen/m² . •Non metric unit of illuminance is foot-candle. LUX METER FOR MEASURING ILLUMINANCE IN WORKING ENVIRONMENT
  • 3. ILLUMINATION TERMINOLOGY IN ILLUMINATION, DEFINITIONS, UNITS AMPERES: •Measurement of current flow is ampere. •Amp. rating is marked on many electric products & special purpose lights to ensure adequate wiring for the application. LUX: •1 lux is equal to the illuminance provided by an ordinary wax candle on a spherical surface with an area equal to 1 sq.m., from 1 m away. • Measure of luminous flux spread over a given area – luminous flux (measured in lumens) is a measure of the total amount of visible light present. •A flux of 1,000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1,000 lux. However, the same 1,000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux. •1 lux = 0.0929 footcandles.
  • 4. ILLUMINATION TERMINOLOGY IN ILLUMINATION, DEFINITIONS, UNITS LUMEN: •The lumen (symbol: lm) is the SI unit of luminous flux, a measure of the total amount of visible light emitted by a source. CANDELA: •The candela (symbol: cd) is the SI unit of luminous intensity; that is, power emitted by a light source in a particular direction. • A common candle emits light with a luminous intensity of roughly one candela. •If emission in some directions is blocked by an opaque barrier, the emission would still be approximately one candela in the directions that are not blocked.
  • 5. ILLUMINATION TERMINOLOGY IN ILLUMINATION, DEFINITIONS, UNITS: FOOT CANDLE (lumen/sq.ft.): •A foot-candle (abbreviated as fc) is a non-SI unit of illuminance or light intensity . • The name "footcandle" conveys “the illuminance cast on a surface by a one-candela source one foot away.” •The unit is defined as the amount of illumination the inside surface of a 1-foot radius sphere would be receiving if there were a uniform point source of one candela in the exact center of the sphere. 1 foot-candle = 1 lumen per square foot. 1 foot candle = 10.764 lux
  • 6. EFFICACY: •Luminous efficacy is a measure of how well a light source produces visible light - measure of the efficiency with which the source provides visible light from electricity. •The efficiency of a lamp measured in ratio of lumens per watt (LPW) – more lumens per watt more efficient the lamp. •A higher LPW means the bulb converts power into light in a more efficient manner. EFFICIENCY: •Light output from a luminaire (fixture) as a % of light output from the bulb it uses. •For instance, a fixture with a fluorescent bulb that emits 1000 lumens may have a shade/cover that decreases the direct light emitted to only 900 lumens. That fixture would be considered 90% efficient.
  • 7. SI PHOTOMETRY UNITS: Quantity SI unit Symbol Luminous flux lumen lm Luminous intensity Candela cd Luminance Candelas per sq.m. cd/m² Illuminance Lux (lumen per sq.m.) lx Luminous efficacy Lumen per watt lm/watt LPW *Luminous flux/luminous power is the measure of the power of light / the measure of the total power of light emitted. LUMINAIRES: •Lighting industry uses this term to indicate ‘lighting fixtures or ‘fittings’. •Luminaires are grouped by mounting type & locations: Ceiling mounted Wall-mounted Architectural Suspended Furniture/cabinet integrated Recessed Plug-in Exterior luminaire
  • 8. GLARE •Glare is difficulty seeing in the presence of bright light such as direct or reflected sunlight or artificial light such as car headlamps at night. •Glare is an interference with visual perception caused by an uncomfortably bright light source or reflection; a form of visual noise. a) Direct glare b) Indirect glare / Reflected glare c) Discomfort glare d) Disability glare e) Blinding glare
  • 9. DIRECT GLARE •Bare bulb glare - eliminate by:  changing a shade adjusting angle of a fixture Replacing bulb with one of a lower wattage Replacing bulb – from clear to frosted – from thinly frosted to thickly frosted. *if necessary add another light source on the ceiling or wall. •In recessed lighting baffles can absorb unwanted light or shield the light source from direct view. •With new furniture layout reassess for glare. For e.g., re-orienting a family room sofa to face a game table might cause those seated on the sofa to look directly up into the exposed bulbs of a suspended pendant fixture.
  • 10. INDIRECT GLARE •Any flat reflective surface can be the source of indirect glare. E.g., shiny desktops, countertops, tables, mirrors, computer screens, glass over pictures, television screen, even enameled or metallic surfaces, window glass. •As obvious as direct glare , reflected / indirect glare can cause eye- strain. •To solve reflected glare problem: Shift light sources Shift furniture
  • 11. GLARE Glare can be divided into following types (depending on magnitude): •Discomfort glare (less severe case): distracting or uncomfortable, which interferes with the perception of visual information required to satisfy biological needs, but which does not significantly reduce the ability to see information needed for activities. •Disability glare (severe situation): renders the task impossible to view - reduces the ability to perceive the visual information needed for a particular activity - such as when driving westward at sunset. •Blinding Glare: so intense that for an appreciable length of time after it has been removed, no visual perception is possible.  Direct glare - glare of a truck light or exposed bulb. Victims of indirect glare may not know the source, but experience headaches, eye strain & general discomfort. A good lighting plan should eliminate direct & indirect glare.