Road Lighting
Visibility of objects
• An object has to be seen against its background:
the road surface
2
Road Lighting principle: Negative contrast
Object is seen against its background
- co
luminance
ntra
s
t
illuminance
3
Revealing power
Visibility: ability of motorist to detect objects
Revealing power is used
in road lighting as a reference
to evaluate visibility of objects
4
Visibility of objects
•
An object has to be seen against its background: the road
surface
• The visibility of the object depends on:
– Object luminance (cd/m2)
5
Visibility of objects
•
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)
6
Road luminance
luminance
illuminance
7
Design parameters
Luminance ( L ) is the brightness of the road surface as seen
by the driver / observer
Lav Expressed in: “cd / m2”
8
Design parameters
Road Luminance (Lav)
9
Road luminance: Observer position
s
60m
w
10
Road luminance: Impact of luminance level
0.50 0.75
11
Road luminance: Key influencing factors
• Lay out
• Photometry
• Light source
Reflection coefficient as per Asphalt CIE R3 : Q0 = 0.07
12
LUMINANCE : Field of calculation
2 luminaires in
a same row
are enclosed
distance
max.100m
distance
60 meter
height of
observer 1.50m
Observer in
the center
of each lane
13
LUMINANCE: Position of calculation points
Spacing of the points in a driving lane :
In the longitudinal direction : D = S / N
In the transverse direction : d = WL / 3
D : spacing between points in the longitudinal direction, in metres
d : spacing between points in the tranverse direction, in metres
S : spacing between luminaires in the same row, in metres
WL : width of the lane, in metres
N : number of calculation points in the longitudinal direction with the following
values:
The outermost calculation points are spaced d/2 from the edges of the
lane.
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).
14
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 lowest
calculated
15
Visibility of objects
•
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
16
Design parameters
Uniformity: Uo , U1
Shows how the light is distributed on the road
17
Overall uniformity: Definition
Overall uniformity is the ratio of the
minimum to the average road luminance
A good overall uniformity ensures
that all spots on the road are
sufficiently visible
18
LUMINANCE: Overall uniformity
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
19
100%
Revealing power: Impact of overall uniformity
50
75
U0=0.4
U0 =0.2
25
Uo= 0.2
0
RP
Uo= 0.4
0.1
0.2
0.5
1
2
5
10 cd/m2
Laverage
20
Overall uniformity: Key influencing factors
• Mounting height ( h )
• Spread
21
Longitudinal uniformity: Definition
•
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 socalled ‘Zebra’ effect
Longitudinal Uniformity
U1 = L-minimum
L-maximum
22
LUMINANCE: Uniformity lengthwise Ul
Calculated for each observer ; the lowest value is
considered
Lmin
Lmax
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.
23
Longitudinal uniformity: Key influencing factors
• Spacing ( S )
• Throw
24
Visibility of objects
•
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
25
Design parameters: Glare
Sensation caused by Brightness of lanterns within the
visual field which is brighter than the adaptation level of
eye.
26
Design parameters: Glare
•
Disability glare reduces the vision
•
Discomfort glare creates unpleasant viewing conditions
• Threshold Increment (TI) represents both types of glare
TI = the % increase in the luminance level required to
make an object equally visible as in the absence of glare
27
100%
Revealing power: Impact of TI
75
UO=0.4
TI =7%
25
50
UO= 0.4
TI =30%
0
RP
0.1
0.2
0.5
1
2
5
10 cd/m2
Laverage
28
Threshold Increment
Threshold increment
Assessment
%
> 20
10
< 10
Operative value of TI shall be the
highest value among observers.
Bad
Moderate
Good
Key influencing factors:
• Lay out
• Photometry
29
Uniformity and glare
Uniform, glare-free lighting :
• Early anticipation when driving
• Smoother traffic flow
• Relaxed drivers
• Increased road capacity
30
Surround ratio: SR
SR is the average horizontal illuminance on
the two longitudinal strips each adjacent to
the two edges of the carriageway and lying
off the carriageway
Divided
by the average horizontal illuminance on the
two longitudinal strips each adjacent to the
edges of the carriageway but lying on the
carriageway
SR = Ekirb / Eroad ≥ 50%
Sufficient lighting in the surrounding of
the road creates a proper adaptation of
the eye
31
Surround ratio: SR
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 equals 5 m :
6
: luminaires
SR(1) = E1/E2
SR(2) = E4/E3
SR = (E1+E4) / (E2+E3)
CIE 115
EN 13201
For dual carriageways, both carriageways together are treated as a single
carriageway unless they are separated by more than 10 m.
32
Surround ratio: SR
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
SR = (E1+E4) / (E2+E3)
EN 13201
33
Surround ratio: SR
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
: obstruction
: luminaires
SR = (E1+E4) / (E2+E3)
EN 13201
34
Summary of lighting design parameters
and related influencing factors
Level
Uniformity
Glare
Visual
performance
Lav
Uo
TI
Visual
comfort
Lav
Ul
TI
↓
• Lay out
( h, S )
• Photometry
• Light source
↓
• Lay out
h → U0
S → U1
• Photometry
↓
• Lay out (h)
• Photometry
35
Norms and recommendations
as per CIE 115-1995
Lighting norms
Lighting
Performance
Total costs
Luminance
Uniformity
Glare
Installation cost
Maintenance cost
Energy
37
Road types
Motorways
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
39
Major roads
Provide main transport
link within city
• Motorized traffic only
• Sometimes, separated carriage way
provided for slow traffic or
pedestrians
• Pedestrian crossings at road junctions
• Traffic speed 50 km/hr to 80 km/hr
• Number of lanes vary from 2 * 2 to 6
40
Minor and residential roads
Provide transport link up to major
road
•
•
•
•
Mixed traffic and pedestrians
Low speed traffic
Number of lanes 2
Many crossings, parking zones etc
41
CIE 115 – Lighting Classes
Description of road
High speed roads
with separate
carriage ways
Eg: motorways
High speed roads,
dual carriage way
roads
Lighting
class
Traffic density and
road complexity
- high
- medium
- low
Traffic control,
separation and mix
- poor
- good
M1
M2
M3
M1
M2
42
CIE 115 – Lighting Classes
Description of
road
Important urban
traffic roads
Less important
roads
Eg: residential and
minor roads
Lighting
class
Traffic control,
separation and mix
- poor
- good
Traffic control,
separation and mix
- poor
- good
M2
M3
M4
M5
43
CIE 115 – Lighting Classes
LIGHT
CLASS
Roads
with few
Junctions
All Roads
Lav.
UO
TI
(min.) (min.) (max.)
U1
(min.)
M1
M2
M3
M4
2.0
1.5
1.0
0.75
0.7
M5
0.5
0.4
0.4
0.4
0.4
0.4
10
10
10
15
15
0.7
0.5
-
Roads with
Footways
Surround
Ratio (min.)
0.5
0.5
0.5
44