road lighting design

Road Lighting

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• An object has to be seen against its background: the road surface

Visibility of objects

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luminance illuminance

- contrast

Object is seen against its background

Road Lighting principle: Negative contrast

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Visibility: ability of motorist to detect objects

Revealing power

Revealing power is usedin road lighting as a reference to evaluate visibility of objects

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• The visibility of the object depends on:– Object luminance (cd/m2)


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• The visibility of the object depends on:– Object luminance (cd/m2)– Road luminance (cd/m2)


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luminanceluminance

illuminanceilluminance

Road luminance

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Luminance ( L ) is the brightness of the road surface as seen by the driver / observer

Lav Expressed in: “cd / m2”

Design parameters

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Road Luminance (Lav)

Design parameters

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w

s

60m

Road luminance: Observer position

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Road luminance: Impact of luminance level

0.750.50

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Reflection coefficient as per Asphalt CIE R3 : Q0 = 0.07

• Lay out• Photometry• Light source

Road luminance: Key influencing factors

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distance60 meter

distance

max.100m

height of observer 1.50m

2 luminaires in a same row are enclosed

Observer in the center

of each lane

LUMINANCE : Field of calculation

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In the longitudinal direction : D = S / ND : spacing between points in the longitudinal direction, in metres

S : spacing between luminaires in the same row, in metres

N : number of calculation points in the longitudinal direction with the following values:

for S ≤ 30 m, N = 10;

for S > 30 m, the smallest integer giving D ≤ 3 m The first transverse row of calculation points is spaced at a distance D/2 beyond the first luminaire (remote from the observer).

Spacing of the points in a driving lane :

In the transverse direction : d = WL / 3d : spacing between points in the tranverse direction, in metres

WL : width of the lane, in metres

The outermost calculation points are spaced d/2 from the edges of the lane.

LUMINANCE: Position of calculation points

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LUMINANCE: Position of observer

• Observer is located at the centre of each lane• Observer´s eye is 1,5 m above the road level

Operative value of average luminance is the lowestcalculated

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• The visibility of the object depends on:– Object luminance (cd/m2)– Road luminance (cd/m2)– Luminance uniformity


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Uniformity: Uo , U1Shows how the light is distributed on the road

Design parameters

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Overall uniformity is the ratio of the minimum to the average road luminance

A good overall uniformity ensuresthat all spots on the road are sufficiently visible

Overall uniformity: Definition

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It is calculated for each observer, the lowest value is considered :Uo = Lmin/Lave

Lmin is the lowest luminance occuring at any grid point in the field of calculation

.Lmin

Lave

LUMINANCE: Overall uniformity

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RP

0

25

5

0

7

5

10

0%

0.1 0.2 0.5 1 2 5 10 cd/m2

Laverage

U0=0.4

U0 =0.2

Revealing power: Impact of overall uniformity

Uo= 0.4

Uo= 0.2

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• Mounting height ( h )• Spread

Overall uniformity: Key influencing factors

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Longitudinal UniformityU1 = L-minimum

L-maximum

• Longitudinal uniformity is the lowest ratio of the minimum to the maximum road luminance in the middle of each lane

• A good longitudinal uniformity ensures comfortable driving conditions without the so-called ‘Zebra’ effect

Longitudinal uniformity: Definition

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Calculated for each observer ; the lowest value is considered

The number of points in the longitudinal direction (N) and the spacing between them shall be the same as those used for the calculation of average luminance.

LUMINANCE: Uniformity lengthwise Ul

Lmin Lmax

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Longitudinal uniformity: Key influencing factors

• Spacing ( S )• Throw

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• The visibility of the object depends on:– Object luminance (cd/m2)– Road luminance (cd/m2)– Luminance uniformity– Glare control


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Sensation caused by Brightness of lanterns within the visual field which is brighter than the adaptation level of eye.

Design parameters: Glare

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• Disability glare reduces the vision

• Discomfort glare creates unpleasant viewing conditions

• Threshold Increment (TI) represents both types of glareTI = the % increase in the luminance level required to make an object equally visible as in the absence of glare

Design parameters: Glare

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RP

0

25

5

0

7

5

10

0%

0.1 0.2 0.5 1 2 5 10 cd/m2

Laverage

UO=0.4TI =7%

UO= 0.4TI =30%

Revealing power: Impact of TI

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Threshold increment Assessment

%

> 20 Bad

10 Moderate

< 10 Good

Key influencing factors:• Lay out• Photometry

Threshold Increment

Operative value of TI shall be the highest value among observers.

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Uniform, glare-free lighting :• Early anticipation when driving• Smoother traffic flow• Relaxed drivers• Increased road capacity

Uniformity and glare

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SR is the average horizontal illuminance on the two longitudinal strips each adjacent to the two edges of the carriageway and lying off the carriagewayDividedby the average horizontal illuminance on the two longitudinal strips each adjacent to the edges of the carriageway but lying on the carriageway

Surround ratio: SR

Sufficient lighting in the surrounding of the road creates a proper adaptation of the eye

SR = Ekirb / Eroad ≥ 50%

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: luminaires

EN 13201SR = (E1+E4) / (E2+E3)CIE 115SR(1) = E1/E2 SR(2) = E4/E3

The width of all four strips shall be the same, and equal to 5 m, or half the width ofthe carriageway.

Location of strips with width of strip equals 5 m :

For dual carriageways, both carriageways together are treated as a single carriageway unless they are separated by more than 10 m.

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Surround ratio: SR

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The width of all four strips shall be the same, and equal to 5 m, or half the width of the carriageway.

Location of strips with width of strip less than 5 m because width of carriageway is less than 10 m

: luminaires

EN 13201SR = (E1+E4) / (E2+E3)

Surround ratio: SR

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In case of obstruction, the width of the unobstructed strip lying off the carriageway is applied on the 4 parts.

Location of strips with width of strip less than 5 m because of obstruction

: luminaires

: obstruction

EN 13201SR = (E1+E4) / (E2+E3)

Surround ratio: SR

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Level Uniformity Glare

Visual performance

Lav Uo TI

Visual comfort

Lav Ul TI

↓• Lay out

( h, S )• Photometry• Light source

↓• Lay out

h → U0S → U1

• Photometry

↓• Lay out (h)• Photometry

Summary of lighting design parametersand related influencing factors

Norms and recommendationsas per CIE 115-1995

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LightingPerformance

LuminanceUniformity

Glare

Total costs

Installation costMaintenance cost

Energy

Lighting norms

Road types

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Provide main transport link between the towns

• Motorized traffic only • Separated carriage ways• No pedestrian crossing • High speed traffic

(80 km/hr to 150 km/hr)

• Number of lanes vary from 2 * 2 to 6

Motorways

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Provide main transportlink within city

• Motorized traffic only • Sometimes, separated carriage way

provided for slow traffic orpedestrians

• Pedestrian crossings at road junctions• Traffic speed 50 km/hr to 80 km/hr

• Number of lanes vary from 2 * 2 to 6

Major roads

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Provide transport link up to majorroad

• Mixed traffic and pedestrians• Low speed traffic• Number of lanes 2 • Many crossings, parking zones etc

Minor and residential roads

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Description of road Lighting class

High speed roads with separate carriage ways Eg: motorways

Traffic density and road complexity - high - medium - low

M1 M2 M3

High speed roads, dual carriage way roads

Traffic control, separation and mix - poor - good

M1 M2

CIE 115 – Lighting Classes

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Description of road

Lighting class

Important urban traffic roads


M2 M3

Less important roads Eg: residential and minor roads


M4 M5


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LIGHTCLASS All Roads

Roadswith fewJunctions

Roads withFootways

Lav. UO TI U1SurroundRatio (min.)

M1M2M3M4M5

2.0 1.5

0.750.5

1.0

0.40.40.40.40.4

1010101515

0.70.70.5--

0.50.50.5--

(min.) (min.) (min.)(max.)


road lighting design

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