1
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Explain the term : Light
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Light
· It is small part of electromagnetic radiation which
is sandwich between ultraviolet and infrared radiation.
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2
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Explain the laws of illumination.
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Laws of
illumination
Inverse square law
· This law states that the illumination of a surface
is inversely proportional to the square of the distance between surface and a
point of light source.
· This law is applicable if the surface is normal to
the line of flux.
Lambert’s cosine law
· This law states that the illumination at any point
on the surface is directly to the cosine of angle between the normal at that point
and line of flux.
· This law is applicable if the surface is inclined at
angle θ to the line of flux.
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3
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Explain the following terms with regard to illumination : Luminous
flux, Lumen and Luminous intensity
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Luminous flux
· It is defined as the light wave emitted per second
from a luminous body.
Lumen
· It is the unit of luminous flux.
Lumen
= candle power of light source × solid angle
Luminous intensity
· It is defined as the luminous flux emitted by the
electrical source per unit solid angle.
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4
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Explain the following terms with regard to illumination : Candle
power, Illumination and Lux
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Candle power
· It is defined as the total luminous flux lines
emitted by light source in a unit solid angle. Its unit is candela or
lumen/streadian
Illumination
· It is defined as the luminous flux received by the
unit surface area. Its unit is Lux.
Illumination
= Luminous flux / Area
Lux
· It is defined as the illumination flux of one lumen
uniformly distributed over a radius of 1 meter from the centre of sphere.
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5
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Explain the following terms with regard to illumination : MHCP , MSCP
and MHSCP
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Mean horizontal candle power ( MHCP )
· It is defined as the mean of candle power of source
in the direction of the horizontal plane.
Mean spherical candle power ( MSCP )
· It is defined as the mean of candle power of source
in all the direction.
Mean hemispherical candle power ( MHSCP )
· It is defined as the mean of the candle power of
source in all the direction above or below of the horizontal plane.
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6
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Explain the following terms with regard to illumination : Specific consumption , Utilization
factor and Depreciation factor
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Specific consumption
·
It is
defined as the ratio of the electrical power input to the source to the
average candle power of it.
·
Specific
consumption = Electrical power input / Average candle power
Utilization factor
· It is defined as the ratio of the total lumen
reaching to the working plane to the total lumen emitted by the light source.
Utilization
factor = Total lumen at working plane / Total lumen emitted by light source
Depreciation factor
·
It is
defined as the ratio of the initial illumination to the ultimate
illumination.
·
Depreciation
factor = 1 / Maintenance factor
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7
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Explain the following terms with regard to illumination : Maintenance factor, Absorption factor and Lamp efficiency
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Maintenance factor
· It is defined as the ratio of the illumination under normal condition to
the illumination when the system is new.
· Maintenance factor =
Illumination at normal condition / Illumination when system is new
Absorption
factor
· When atmosphere is full of smoke and fumes, there is
a possibility that absorption of light. Therefore total lumen available after
absorption is reduced.
- The
absorption factor is defined as the ratio total lumen available after
absorption to the total lumen emitted by the light source.
Absorption
factor = Lumen available after absorption / Lumen emitted by light source
Lamp
efficiency ( Luminous efficiency )
· It is defined as the ratio of the luminous flux
emitted by the light source to the electrical input supplied to the light
source.
·
Lamp
efficiency = Luminous flux emitted by light source / Electrical input to the
light source
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8
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Describe the function of lamp.
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Lamp
· The lamp is equipment which produces light.
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9
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Describe the main disadvantages of filament lamps.
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Disadvantages
of filament lamps
· Very sensitive to voltage fluctuation
· Short lamp life
· High power consumption ( 15Watt / lamp )
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10
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Describe the advantages of LED lamps over filament lamps.
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Advantages
of LED lamps over filament lamps
· Withstand against voltage fluctuation
· Long life
· Low power consumption ( < 1 Watt / LED)
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11
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Describe the function of luminaries in a lighting system. What does
the luminaries consist of?
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Function
of luminaries
· The luminaries are a device which transforms the
light emitted from one or more lamps. The luminaries consists of lamp, lamp
socket, lamp housings, electronics Ballast and reflective material.
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12
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Write the full form of CRI.
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The full form of the CRI is colour rendering index.
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13
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Write the full form of CFL lamp.
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The full form of the CFL lamp is compact fluorescent lamp.
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14
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Describe the advantages of electronic ballasts over conventional
ballasts.
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Advantages of
electronic ballast over conventional ballasts
·
Instant start or
lighting
·
Less heat
generated
·
Higher power
factor
·
Consume very
less energy as compared to conventional ballast
·
Lamp life
increases
·
Less weight
·
Noiseless
operation
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15
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Describe the advantages of CFL lamps over Incandescent lamps?
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Advantages
of CFL lamps over incandescent lamps
· Longer lamp life (Approx. 10,000 hours)
· Higher illumination( 50 – 55 lumen / watt )
· Less heat generation
· Energy saving
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