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Road Lighting
2
• An object has to be seen against its background: the road surface
Visibility of objects
3
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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• An object has to be seen against its background: the road surface
• The visibility of the object depends on:– Object luminance (cd/m2)
Visibility of objects
6
• An object has to be seen against its background: the road surface
• The visibility of the object depends on:– Object luminance (cd/m2)– Road luminance (cd/m2)
Visibility of objects
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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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• An object has to be seen against its background: the road surface
• The visibility of the object depends on:– Object luminance (cd/m2)– Road luminance (cd/m2)– Luminance uniformity
Visibility of objects
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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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• An object has to be seen against its background: the road surface
• The visibility of the object depends on:– Object luminance (cd/m2)– Road luminance (cd/m2)– Luminance uniformity– Glare control
Visibility of objects
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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.
6
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
Traffic control, separation and mix - poor - good
M2 M3
Less important roads Eg: residential and minor roads
Traffic control, separation and mix - poor - good
M4 M5
CIE 115 – Lighting Classes
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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.)
CIE 115 – Lighting Classes