Street Lighting: (i) Methods of light distribution. (ii) Design of street lighting system. (iii)Definitions- Luminaire, foot candle, Lumen, utilization and maintenance factors. (iv) Different types of light sources used for street lighting. (v) Fundamental factors of night vision

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PREPARED BY : ASST. PROF. VATSAL D. PATEL
MAHATMA GANDHI INSTITUTE OF
TECHNICAL EDUCATION &
RESEARCH CENTRE, NAVSARI.

2.  The main purpose of street lighting is to enable the road user
to see accurately the carriageway and the immediate
surroundings in darkness. Majority of road accidents are
caused in the night and poor lighting is the main cause of
accidents.
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3.  Driving in the night is facilitated by the head lights, but it is
always not possible to depend on head lights. Improved
visibility at night by means of artificial lighting lessens the
strain on driving and ensures comfort.
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4.  Highway lighting is particularly more important at
intersections, bridge site, level crossing and places where there
is restriction of traffic to movements.
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5.  1. Amount and distribution of light flux from the lamps
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6.  2.Size of object
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7.  3.Brightness of object and background
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8.  4.Reflecting characteristics of the pavement surface
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9.  5.Glare on the eyes of the driver
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10.  6.Time available to see an object
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11.  Luminous flux (Ф):
 This is the radiant power given by light source.
 It’s unit is lumen.
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12.  Lumen (lm):
 This is the SI unit of luminous flux.
 It is equal to the amount of flux received on surface area of
one square meter of sphere, when a light source of one candle
power placed at its centre.
 Lumen = candle power X solid angle
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13.  Steradian:
 A steradian is the unit measure of a solid angle.
 Solid angle = ω
 It is equal to the solid angle subtended at the centre of a sphere
by unit area of its surface. The whole space surrounding a
point subtends a solid angle of 4π.
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14.  Luminous Intensity (I):
 Luminous flux emitted per unit solid angle is called luminous
intensity.
 I =
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15.  Candela:
 It is the unit of luminous intensity. Luminous intensity
expressed in candelas is called candle power.
 Metre Candela:
 It is the normal incident illumination produced by unit candle
power at a distance of one meter.
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16.  Illumination (E):
 It is the measure of the amount of light flux which falls on a
surface. It is independent of the direction from which the light
comes or the size of light sources or their positions.
Illumination is same if surface is white or black.
 E = ………….. Lumen/m2
 1 lumen/m2 = 1 lux
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17.  Luminance (Brightness):
 The luminous intensity emitted or reflected per unit area of a
surface is called luminance.
 B =
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18.  Glare:
 Condition of vision in which there is discomfort or a reduction
in the ability to see significant objects or both, due to an
unsuitable distribution of luminance or to extreme contrasts in
space or time.
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19.  Luminare (Lantern):
 A house for one or more lamps, comprising a body and any
refractor, reflector, diffuser or enclosure associated with the
lamps.
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20.  Lighting installation:
 The entire equipment provided for lighting a street section,
and consists of lanterns, means of support and the electrical
auxiliaries.
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21.  The total output of a point light source will naturally radiate
uniformly from the point with equal intensity in all direction.
 It is evident that such light distribution would be insufficient
and uneconomical when the purpose is to direct the light
toward a relatively limited area, such as pavement of a street.
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22.  There are mainly three type of Distribution of Light like,
1. Glare
2. Vertical Distribution of light
3. Lateral Distribution of light
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23.  The amount of glare present is dependent on,
1. Brightness of glare Source
2. Angle of incidence with respect to the normal line of
vision
3. General level of illumination
4. Area of glare Source
5. Distance of Glare source from the observer.
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24.  The glare from luminaries may be controlled by:
1. Increasing the height of mountings
2. Shielding the light source
3. Reducing the brightness contrast of the light source
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25. 1. Cut-off :
 In cut-off system, the light is reduced as completely and as
rapidly as possible above a 70° angle with the downward
vertical, the main beam being usually at this angle. This
system eliminates glare.
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26. 2. Non-cut-off (high angle beam) :
 In non-cut off high angle beam system, the peak intensity is at
about 80° and there is considerable output near the horizontal
plane. With this system, a certain amount of glare is inevitable,
and the modern lighting practice does not favor this system.
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27. 3.Semi-cut-off (medium angle beam) :
 The non-cut-off medium angle beam system is in between
above two systems, with a peak intensity directed at an angle
of 75°.
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28.  The distribution of light in the horizontal direction is equally
important.
 It is not enough that the pavement alone is lighted from
aesthetic considerations.
 The pedestrian footways and the kerbs are also need to be
adequately lighted.
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29.  There are three types of horizontal distribution:
1. Symmetrical distribution
2. Axial distribution
3. Non-axial distribution
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30.  1. Contrast :
 When the brightness of the object is less than that of the
background, that is when the object appears darker than the
road surface.
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31.  2.Glare :
 The disturbing influence when viewing a difficult visual task
under low brightness conditions is known as glare. There are
two types of glare:
1.Disability glare 2.Discomfort glare
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32.  3. Lamps :
 The lamps commonly used for highway lighting are :
Tungsten filament lamps Fluorescent lamps
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33.  3. Lamps :
 The lamps commonly used for highway lighting are :
Sodium vapour lamps Mercury vapour lamps
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34.  4. Luminaire distribution of light :
 It should cover the pavement between the kerbs.
 It should make prominent the traffic signs and other objects
on the road.
 It should illuminate the pavement and the adjacent area to the
extent of about 3m to 5m beyond the pavement edge.
 It should produce maximum uniformity pavement brightness
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35.  5. Lateral placement of lighting poles :
 The lighting poles should not be installed very close to the
pavement edge, because in that case, the capacity of the
roadway is decreased and the free movement of traffic is
obstructed.
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36.  5. Lateral placement of lighting poles :
 IRC has specified the following horizontal clearances for
lighting poles.
For roads with raised kerbs
(as in urban roads)
Min. 0.3 m and desirable 0.6 m from the
edge of raised kerb.
For roads without raised kerbs
(as in rural roads)
Min. 1.5 m from the edge of the
carriageway, subject to min. 5.0 m from
the centre line of the carriageway.
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37.  6. Height and overhang of mounting :
 The distribution of light, shadow and the glare effect from
street lamps depends also on the mounting height.
 The glare on eyes from the mounted lights decreases with
increases in the height of mounting. Usually, mounting height
range from 6 to 10m.
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38.  6. Height and overhang of mounting :
 Overhangs on the lighting poles would keep the poles away
from the pavement edges, but still allow the lamp to be held
above the kerb or towards the pavements.
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39.  7. Spacing of lighting units :
 The spacing between lamps on straight roads is about 3 to 5
times the mounting height.
 For sharp curves, the spacing between lamps is closer for
better visibility conditions.
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40.  8. Lighting layouts :
 Single side lighting
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41.  8. Lighting layouts :
 Both side lighting-opposite
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42.  8. Lighting layouts :
 Both side lighting-staggered
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43.  8. Lighting layouts :
 Central lighting
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44.  For various types of luminaire distribution, the utilization
coefficient charts are available for determination of average
lux of intensity over the roadway surface when lamp lumen,
mounting height width of pavement, and spacing between
lighting poles are known.
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45.  Spacing between lanterns (m) :
 =
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46.  Due to proper street lighting, the police can do better patrol
during night and their job becomes easier and more
manageable.
 Increase in business in city or downtown, are as during night
which would otherwise have been totally not accepted.
 The architects and town planners have found lighting to be a
major source for beautification of their projects.
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47.  Due to good street lighting, there is a considerable reduction in
accident rate during night.
 The illegal action and anti-social activities on the roads are
certainly discouraged by the improved lighting techniques.
 It gives a pleasant atmosphere during night.
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