1.
5 Road Lighting
Er. Romharsh Oli
Lecturer
Everest Engineering College
Road Lighting:
• Lighting has been an instrument to see in the night time.
• Road lighting is primarily intended to enable the road users to see
accurately and easily the carriageway and the immediate
surroundings in the night time.
• The rate of highway accidents and fatalities that occur during night
driving is several times higher than that occur during day driving.
• One of the various causes of increased accident rate during night may
be attributed to poor night visibility.
• Highway lighting or road lighting is particularly more important at
intersections, bridge sites, level crossings and in places where there
are obstructions to traffic movements.
Importance of Road Lighting:
The various importance of road lighting are as follows:
• Minimizes the road accidents at night.
• Enables smooth operation and ensure comfort and confident driving at night.
• Improves the visibility and safety at night.
• Enables road users to see accurately and easily the carriageway and
immediate surroundings in darkness.
• Improve traffic flow conditions during evening peak periods and at night
• Indirect benefits like reduction of crime, feel of security, improves aesthetic
appearance of the surroundings
• Helps to see different traffic signs and signals easily and more clearly during
night time
• Avoid glare problem on eye of the driver.
Factors Influencing Night Visibility:
Various factors that influence night visibility are:
a. Amount and distribution of light flux from the lamps
b. Size of object
c. Brightness of object
d. Brightness of the background
e. Reflecting characteristics of the pavement surface f. Glare on the eyes of the
driver
g. Time available to see an object
Design Factors of Highway Lighting:
The factors to be considered in the design of road lighting are as
follows:
1. Lamps
2. Luminaire distribution of light
3. Spacing of lighting units
4. Height and overhang of mounting
5. Lateral placement
6. Lighting layouts
1. Lamps:
• The choice of lamp, its size and color depends on several
considerations in addition to distribution of light flux on the
pavement surface.
• It is economical to use the largest lamp size, which will provide
sufficient uniformity of pavement brightness; but this also depends
on the spacing of the lamps.
• The various types of lamps in use for highway lighting are filament,
fluorescent and sodium or mercury vapor lamps.
• The choice of lamp for street/highway lighting involves many
considerations such as life, lumen, maintenance, lumen efficiency,
capital costs, annual operating costs, and color appearance, color
rendering qualities, reliability and available lamp ratings.
2. Luminaire Distribution of Light:
• To have the best utility of the luminaire or source of light, it is necessary to
have proper distribution of light.
• The distribution should be downward so that high percentage of lamp light is
utilized for illuminating the pavement and adjacent area.
• The light distribution selected should be the one which would produce
maximum uniformity of pavement brightness.
• The distribution from the luminaire should cover the pavement between the
kerbs and provide adequate lighting on adjacent area such as footpaths or the
shoulders, for 3 to 5 m beyond the pavement edge.
• Illumination is necessary for traffic signs and other objects on the road.
• The average level of illumination requirement on road side may be 20 to 30
lux on important urban roads carrying fast traffic and about 15 lux for other
main roads carrying mixed traffic and in arterial roads.
• In secondary roads the level of illumination requirement may be 4 to 8 lux
depending on traffic.
Cobra Head Style Luminaires
9
Vertical Mount Style Luminaires
10
High Mast Style Luminaires
11
Shoebox Style Luminaires
12
Decorative Style Luminaires
13
Bridge Underpass Luminaire
14
3. Spacing of Lighting Units:
• The spacing of lighting units is often influenced by the electrical
distribution poles, property lines, road layout and type of the
roadside features and their illumination. Large lamps with high
mountings and wide spacing should be preferred from economy point
of view.
4. 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 increase in height of mounting.
Usual mounting heights range from 6 to 10 m.
• 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 pavement. This enables better distribution of light on the
pavement and less glare on eyes of road users. It is desirable to have
higher mounting heights and adequate overhang projections.
5. Lateral Placement:
• The street lighting poles should not be installed close to the
pavement edge.
• If they are too close to the carriageway, the free movement of traffic
is obstructed, resulting in decrease in capacity of roadway.
• Horizontal clearance required for lighting poles as given:
• For roads with raised kerbs (as in urban roads): minimum 0.3 m and desirable
0.6 m from the edge of raised kerb
• For roads without raised kerbs (as in rural roads): minimum 1.5 m from the
edge of the carriageway
6. Lighting Layouts:
• On the straight roads, lighting layout may be of the three types: single
side; staggered, on both sides; central.
• Single side lighting is economical to install, but it is suitable only for
narrow roads. For wider roads with three or more lanes, the
staggered system or central lighting system may be adopted.
• Special care should be taken while locating the lights on curves.
• Lights are installed at closer spacing on curves than on straights.
• The lights are located on the outer side of the curves to provide
better visibility. At intersection, more illumination is required
Design of Highway Lighting System:
