How to Design Efficient Street Lighting-Part-1

Introduction:

  • The basic idea of roadway and Highway lighting is to provide uniform level of illumination on road at horizontal and vertical level and provide a safe and comfortable environment for the night time driver.
  • Lighting design is basic idea of the selection and the location of lighting equipment to provide improved visibility and increased safety.
  • Street lighting systems should be designed in a way to avoid significant differences in luminance levels at the light source and on road areas. Furthermore, continuous variation of lighting levels can cause eye strain and should be avoided, in particular on long roads.
  • Road lighting provides visual conditions for safe, quick and comfortable movement of Road users.

Designing Factor for Street Light:

  • The factors that are playing a vital role in the Road Lighting are following.

(A) Type of Road

  • Road Classification

(B) Street Light Pole

  • Street Light Pole Arrangements
  • Placement of Pole

(C) Lighting Fixture

  • Lighting Fixture Mounting Height
  • Lighting Fixture Classification
  • Lighting Fixture Distributor

(D) Lighting Factors

  • Maintenance Factor
  • Coefficient of Utilization

(E) Lighting Uniformity

  • Lighting Uniformity
  • Surrounding Ratio

(F) Lighting Pollution

  • Glare
  • Sky Glow
  • Trespass

(G) Selection of Luminas

  • Type of Light
  • Watt
  • Lumen
  • CRI
  • Efficiency

(A) Classification As per Road:

Table 4 : Road Classes as per SP 72 (Part 8), IS 1944 (Part 1) and IS 1970

Class A1 Important routes with rapid and dense traffic where safety, traffic speed, and driving comfort are the main considerations
Class A2 Main Roads with considerable volume of mixed traffic, such as main city streets, arterial roads and thoroughfares.
Class B1 Secondary roads with considerable traffic such as main local traffic routes, shopping streets
Class B2 Secondary roads, with light traffic
Class C Lighting for residential and unclassified roads not included in previous groups
Class D Lighting for bridges and flyovers
Class E Lighting for town and city centers
Class F Lighting for roads with special requirement such as roads near air fields, railways and docks

 

TYPE OF ROAD

TYPE OF ROAD DENSITY OF TRAFFIC TYPE EXAMPLE
A Heavy and high speed motorized traffic Road with fixed separators, No crossings for very long distance National highways or state highways or called interstate highways, express ways or motor ways
B Slightly lower density and lower speed traffic termed Road which is made for vehicular traffic with adjoining streets for slow traffic and pedestrians as we find in metros Trunk road or major road in a city
C Heavy and moderate speed traffic Important urban roads or rural roads. they do not interfere with the local traffic within the town Ring roads
D Slow traffic, pedestrians Linking to shopping areas and invariably the pedestrians, approach road Shopping street, trunk road
E Limited speed. Slow or mixed traffic predominantly pedestrians, Local streets, collectors road

(B) Street Light Pole:

(1) Street Light Arrangement:

  • There are four basic types of street lighting layout arrangements used for streets or highways illumination.
  • (a) One Side Pole Layout:
  • Arrangement: In One Side Pole Layout, all luminaries are located on one side of the road.
  • Road Width: For narrower roads.
  • Pole Height: The installation height of the lamp be equal to or less than the effective width of the road surface.

  • Advantage: There are good indelibility and low manufacturing cost.
  • Disadvantage: The brightness (illuminance) of the road on the side where the lamp is not placed is lower than the on which side the light pole is placed.

(b) Both Side Staggered Pole Layout:

  • Arrangement: In the staggered arrangement, the luminaires are placed alternately on each side of the road in a “zig-zag” or staggered fashion.
  • Road Width: For Medium Size roads.
  • Pole Height: The installation height of the lamp is equal or 1.5 time the effective width of the road.

  • Advantage: This type of arrangement is better than single side arrangement.
  • Disadvantage: Their longitudinal luminance uni­formity is generally low and creates an alternating pattern of bright and dark patches. However, during wet weather they cover the whole road better than single-side arrangements.

(c) Both Side opposite Pole Layout:

  • Arrangement:
  • In Both Side Opposite Pole Layout, the luminaries located on both sides of the road opposite to one another.
  • Road Width: For Medium Size roads.
  • Pole Height: The installation height of the lamp will be 2 to 2.5 time the effective width of the road.

  • Advantage: op­posite arrangements may provide slightly better lighting under wet conditions.
  • Disadvantage:
  • If the arrangement is used for a dual carriageway with a central reserve of at least one-third the carriageway with, or if the central re­serve includes other significant visual obstructions (such as trees or screens), it effectively becomes two single-sided arrangements and must be treated as such.

 (d) Twin-central Pole Layout:

  • Arrangement: In Twin central arrangement, the luminaries are mounted on a T-shaped in the middle of the center island of the road. The cen­tral reserve is not too wide, both luminaires can contribute to the luminance of the road surface on either lane.
  • Road Width: For Large Size roads.
  • Pole Height: The installation height of the lamp be equal to the effective width of the road.

  • Advantage: This arrangement generally more efficient than opposite arrangements. However, op­posite arrangements may provide slightly better lighting under wet conditions.

(2) Proper Placement of Pole:

(i) Setback

  • Set back is the horizontal distance between the face of a light pole and the edge of traveled way.
  • Placing luminaries too close to a vertical surface results in hotspots at its base.
  • A setback of 3 foot to 4 foot works well for many applications.
  • Light from luminaires at extremely short setbacks grazes the surface and enhances its texture.
  • Light from luminaries at Long setbacks (Luminaries too far from a vertical surface) cause shadows at low levels.
  • Longer setbacks may be required for taller surfaces.
  • Scallops between fixtures become more noticeable as setback increases.
  • As setback (or spacing) distance increases, Light levels and uniformity decrease.

 

Set Back (BS 5489)

Design Speed Pole Set Back
50 Km/Hr 0.8 Meter
80 Km/Hr 1 Meter
100 Km/Hr 1.5 Meter
120 Km/Hr 1.5 Meter

 

(ii) Overhang

  • Overhang is the horizontal distance between the center of a luminaries mounted on a bracket (Nadir) and the adjacent edge of a carriage way or traveled way.
  • In general, overhang should not exceed one fourth of the mounting height to avoid reduced visibility of curbs, obstacles, and footpaths.

(iii) Outreach

  • Outreach is the horizontal distance between the center of the column and the center of the luminaries and is usually determined for architectural aesthetic considerations.

(iv) Pole Boom(Arm) Length:

  • The use of an arm places the light source closer to the traveled way while allowing the pole to be located further from the edge of the traveled way.
  • Depending on the application, Pole arms may be single and/or double mast arms or davit arms at the top of the pole.
  • There are several different arm lengths and styles of arms that are used.

(v) Arm Type:

  • Type A bracket an arm has a single member arm. It is used when the Arm length is less than 3.5 Meter.
  • Type B bracket arm has a two member truss arm design. Type B arms are used when the Arm length is more than 3.5 Meter.

(vi) Arm Lengths:

  • The length of the bracket arm is dependent upon a street width, pole location in relation to the curb and the presence of a median.
  • Type A (Single member bracket) arms are available in 2 Meter and 2.5 Meter lengths.
  • Type B (Twin member bracket) arms are available in 3.5 Meter, 4 Meter and 5 Meter Lengths.
  • Pole Height is 10 Meter: On typical streets that are 12 Meter’ wide from curb to curb, either a 2 Meter or 2.5 Meter arm is used. Depending on whether the pole is located behind the sidewalk or in the grass parkway between the sidewalk and the curb, the arm length may need to be increased to 4 Meter.
  • Pole Height is 13 Meter: On an undivided street, generally Meter, 2.5 Meter or 4 Meter arms are used.
  • Pole Height is 13 Meter: divided Street, typically have a 8 Meter wide center median to divide opposing lanes of traffic. On streets where the light poles are installed in a raised median, two 4 Meter arms oriented 180° apart are used.

(vii) Boom Tilt Angle (Boom Angle)

  • When the angle of tilt is larger, a uniformity ratio is increasing. Otherwise discomfort glare is increasing because strong light comes into driver’s eyes. So the angle of tilt shall be kept from 15° to 30°.

 

Tilt Angle

Pole Height Arm Length Arm Tile Angle
6 Meter 0.5 Meter 5°,10°,15°
8 Meter 1 Meter 5°,10°,15°
10 Meter 1.5 Meter 5°,10°,15°
>=12 Meter 2 Meter 5°,10°,15°

(viii) Pole Height:

  • Light poles for conventional highway lighting applications support luminaire mounting heights ranging from approximately 30 ft to 50 ft (9.1 m to 15.2 m).
  • Light towers for high-mast lighting applications generally range from 80 ft to 160 ft (24.4 m to 48.8 m) and are designed in multiple sections.
  • Weathering steel is a common material choice for light towers.
  • Ornamental light Poles used for local streets generally range in height for 8 ft to 15 ft (2.4 m to 4.5 m).

 

Pole Height Application
< 6 Meter Majority of side streets or alleys, Public gardens and parking Area to make people feel safe
8 Meter Urban traffic route , the multiplicity of road junctions
10 Meter Urban traffic routes
12 Meter Heavily used routes
18 Meter High mast lighting poles shall be installed at large-scale area such as airports, dockyards, large industrial areas, sports areas and road Intersections.

 (ix) Poles distance from Curb (Offset):

  • The lighting poles should not be installed very close to the pavement edge, because the capacity of the roadway is decreased and the free movement of traffic is obstructed.
  • For roads with raised curbs (as in urban roads) =Min. 0.3 meter and desirable 0.6 meter from the edge of raised curb.
  • For roads without raised curbs (as in rural roads)=Min. 1.5 meter from the edge of the carriageway, subject to min. 5.0 meter from the center line of the carriageway.
  • Height and overhang of mounting
  • The glare on eyes from the mounted lights decreases with increases in the height of mounting. Usually, mounting height range from 6 to 10m.
  • Overhangs on the lighting poles would keep the poles away from the pavement edges, but still allow the lamp to be held above the curb or towards the pavements.

(x) Pole to Pole Spacing

  • Spacing is the distance, measured along the center line of the road, between successive luminaries in an installation.
  • To preserve longitudinal uniformity, the space height ratio should generally be greater than 3.
  • Placing luminaries too far apart creates scallops at the base of the surface.
  • Spacing distances that are equal to 3 to 4 times the setback work well for many applications.
  • Placing luminaries closer together eliminates scallops.
  • Uniformity and light levels increase as spacing (or setback) distances decrease.
  • Spacing of luminaires normally does not exceed five to six mounting heights.
  • The span must not be more than 45 meters and for an average of 20-30 meters.

 

Lighting Pole details as per Road

Road Road Width (Meter) Pole Arrangement Lamp (Watts) Pole to Pole Spacing (Meters) Mounting Height, (Meters) Arm Length, (Meters)
Expressway 10 Twin Central 250 25 To 35 12 1.5
15 250 20 To 35 12 3.0
20 Opposite 250 20 To 45 12 1.5
25 250 20 To 40 12 1.5
30 250 20 To 30 12 1.5
36 250 20 To 25 12 1.5
40 250 20 To 22 12 1.5
Major 10 One-side 250 10 To 40 10 1.5
15 250 10 To 45 12 3.0
10 Twin Central 150 20 To 37 10 1.5
15 250 20 To 43 12 3.0
20 Opposite 150 20 To 40 10 3.0
25 250 20 To 45 10 1.5
30 250 20 To 45 10 1.5
36 250 20 To 45 12 3.0
40 250 20 To 45 2 3.0
Collector 10 One-side 150 10 To 40 10 1.5
15 250 10 To 50 12 3.0
10 Twin Central 150 20 To 40 10 1.5
15 150 20 To 37 12 3.0
20 Opposite 150 20 To 47 10 1.5
25 250 20 To 48 10 1.5
Rural
Highway
8 One-side 150 10 To 38 8 1.5
10 150 10 To 37 8 3.0
15 150 15 To 38 10 3.0
10 Twin Central 150 20 To 45 10 3.0
15 150 20 To 39 12 3.0
20 1.5
Minor 4 One-side 70 10 To 40 8 1.5
6 70 10 To 40 8 1.5
8 70 10 To 40 8 1.5
10 70 10 To 39 8 1.5
10 Twin Central 70 20 To 35 8 1.5
15 Staggered 70 10 To 20 8 1.5
15 Opposite 70 20 To 40 8 1.5

 

Illumination Level

Classification  Average Illumination (lux) Ratio Minimum to average illumination
Class A1 30 0.4
Class A2 15 0.4
Class B1 8 0.3
Class B2 4 0.3

 

Relationship between Mounting Height and Spacing of Fixtures

Pole Arrangement Cut-off type Semi cutoff type
Height Spacing Height Spacing
Single side >=0.7 X Width of Road <=3 X Fixture Mounting Height >=0.8 X Width of Road <=3.5 X Fixture Mounting Height
Both Side Staggered >=1.5 X Width of Road <=3.5 X Fixture Mounting Height >=1.7 X Width of Road <=4 X Fixture Mounting Height
Both Side Opposite >=0.5 X Width of Road <=3 X Fixture Mounting Height >=0.6 X Width of Road <=3.5 X Fixture Mounting Height
Twin central >=0.7 X Width of Road <=3.5 X Fixture Mounting Height >=0.8 X Width of Road <=4 X Fixture Mounting Height

 

 Pole to Pole Distance vs Lux Level

Pole Height Lamp Pole to Pole Distance Max. Illumination (Lux) Average (Lux)
4 Meter 15 watt 12 to 18 Meter 25 18
5 Meter 18 watt 14 to 20 Meter 30 18
6 Meter 30 watt 18 to 24 Meter 32 20
7 Meter 50 watt 21 to 28 Meter 32 20
8 Meter 100 watt 24 to 32 Meter 40 22
9 Meter 110 watt 27 to 35 Meter 34 20
10 Meter 140 watt 30 to 40 Meter 35 22
12 Meter 180 watt 30 to 40 Meter 33 23
14 Meter 200 watt 30 to 40 Meter 30 21

 

Lux Vs Mounting Height

Fixtures (Lux) Mounting Height
3000 to 10000 Lux 6 to 7 Meter
10000 to 20000 Lux 7 to  9 Meter
More than 20000 Lux More than 9 Meter

 

Road – Pole Details

Road Road Type Type of Pole positions Individual Carriageway Width (Meter) Central Verge (Meter) Pole Height above Ground (Meter) Maximum Pole to Pole Spacing (Meter) Clearance from Road Edge (Meter) Bracket Length (Meter) Tilt Angle Lighting Specifications Lamp (Watt)
A1 Dual Carriage Central Verge 10 1.2 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Dual Carriage Central Verge 11 1.2 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Dual Carriage Central Verge 12 1.2 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Dual Carriage Central Verge 14 1.2 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Dual Carriage Central Verge 16 1.2 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Single Carriage Opposite 12 0 12 35 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 250W
A1 Single Carriage Opposite 14.5 0 12 35 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 250W
A1 Single Carriage Opposite 16 0 12 40 0.6 Around one meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Single Carriage Opposite 18 0 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Single Carriage Opposite 21 0 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
Single Carriage Opposite 25 0 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Single Carriage Opposite 31 0 12 40 0.6 1 meter  10° 35 lux/ 0.4/
0.33
HP SV 400W
A2 Single Carriage Single Sided 10 11 30 0.6 < 1.0 meter  10° 25 lux
/0.4/ 0.33
HP SV 250W
A2 Single Carriage Single Sided 9 11 30 0.6 < 0.5 meter  10° 25 lux
/0.4/ 0.33
HP SV 250W
A2 Single Carriage Single Sided 7 11 30 0.6 < 0.5 meter  10° 25 lux
/0.4/ 0.33
HP SV 250W
A2 Single Carriage Single Sided 7 11 30 0.6 < 0.5 meter  10° 25lux
/0.4/ 0.33
HP SV 250W
A3 Single Carriage Single Sided 7 8 20 0.6 < 0.5 meter  10° 20lux
/0.4
HP SV 150W
Pedestrian Pathway Single Carriage Single Sided 3m-6m 7.5 20-25 0.6 <0.5 meter  10° 20 lux
/0.4
HP SV 150W

 

Pole Data

Poles (Meter) Top Dia (mm) Bottom Dia (mm) Thickness (mm) Base plate (mm) Single Arm Bracket (mm) Double Arm Bracket (mm)
3 70 130 3 200x200x12 1000 NA
3 70 130 3 200x200x12 NA 1000
4 70 130 3 200x200x12 1000 NA
4 70 130 3 200x200x12 NA 1000
4 70 130 3 200x200x12 1000 NA
5 70 130 3 200x200x12 NA 1000
5 70 130 3 200x200x12 1000 NA
6 70 130 3 200x200x12 NA 1000
6 70 130 3 200x200x12 1000 NA
7 70 135 3 225x225x16 1000 NA
7 70 135 3 225x225x16 NA 1000
8 70 135 3 225x225x16 1000 NA
8 70 135 3 225x225x16 NA 1000
9 70 155 3 260x260x16 1000 NA
9 70 155 3 260x260x16 NA 1000
9 70 175 3 275x275x16 1000 NA
9 70 175 3 275x275x16 NA 1000
10 70 175 3 275x275x16 1000 NA
10 70 175 3 275x275x16 NA 1000
10 70 200 3 290x290x16 1000 NA
10 70 200 3 290x290x16 NA 1000
11 70 210 3 320x320x20 1000 NA
11 70 210 3 320x320x20 NA 1000
12 70 230 3 325x325x20 1000 NA
12 70 230 3 325x325x20 NA 1000

 

Recommended Levels of Illumination (BIS 1981) (IS 1944)

Type of Road Road Characteristics Road Width (Meter) Average Level of Illumination on Road Surface in Lux Ratio of Minimum/Average Illumination Ratio of Minimum/Max Illumination Type of Luminaire Preferred Luminas Mounting Height
A-1 Important traffic routes carrying fast traffic >10.5,12,14,16,18,20,30 30 0.4 33 Cutoff 9 To 10 Meter
A-2 Main roads carrying mixed traffic like city main roads/streets, arterial roads, throughways > 7 m up to 10 m 15 0.4 33 Cutoff 9 To 10 Meter
B-1 Secondary roads with considerable traffic like local traffic routes, shopping streets < 7m Colony Roads 8 0.3 20 Cutoff or semi-cutoff 7.5 To 9 Meter
B-2 Secondary roads with light traffic 4m,5m, 6m 4 0.3 20 Cutoff or semi-cutoff 7.5 To 9 Meter

About Jignesh.Parmar (B.E,Mtech,MIE,FIE,CEng)
Jignesh Parmar has completed M.Tech (Power System Control), B.E(Electrical). He is member of Institution of Engineers (MIE) and CEng,India. Membership No:M-1473586.He has more than 16 years experience in Transmission -Distribution-Electrical Energy theft detection-Electrical Maintenance-Electrical Projects (Planning-Designing-Technical Review-coordination -Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He has published numbers of Technical Articles in “Electrical Mirror”, “Electrical India”, “Lighting India”,”Smart Energy”, “Industrial Electrix”(Australian Power Publications) Magazines. He is Freelancer Programmer of Advance Excel and design useful Excel base Electrical Programs as per IS, NEC, IEC,IEEE codes. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & Knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

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