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	Twin Central	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	One-side	250	10 To 45	12	3.0
	10	Twin Central	150	20 To 37	10	1.5
	15	Twin Central	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	One-side	250	10 To 50	12	3.0
	10	Twin Central	150	20 To 40	10	1.5
	15	Twin Central	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
Pole Arrangement	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
A1	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 Met