Good Lighting for Safety on Roads, Paths and Square.pdf

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Roads, Paths and Squares

Content

In 2005, 2,143 of 5,361 roads deaths in

Germany occurred on quiet roads at

night; 31.6% of the road users who

were seriously injured were involved in

accidents at twilight or after dark.

Good road lighting improves visual

performance and reduces accidents

by an average of 30%.

As illuminance increases, the

incidence of car theft, burglaries,

physical and sexual assault and

other forms of night crime sharply

decreases.

With a connected load

of 13W per person, the

electricity consumed by

road lighting works out

at just 55 kWh a person

a year.

Seeing and being seen

Bases for planning

Lighting management

Road lighting and costs

Road lighting and the environment

Road lighting and safety

A1, A2, A3 lighting situation roads

B1, B2 lighting situation roads

Road lighting costs

17.15 euros per person

a year, only 7.15 euros

of which is for electri-

city.

D3, D4 lighting situation roads

Conflict areas

Pedestrian crossings

Traffic-calmed zones (E2)

Cyclepaths (C1)

Pedestrian precincts and squares (E1)

Parks and gardens

Outdoor car parks (D2)

Station forecourts and bus stations (D2)

Tunnels and underpasses

Lamps

Luminaires

Standards and literature

Acknowledgements for photographs

Imprint

Information from Fördergemeinschaft

Gutes Licht

Seeing and being seen

Light and vision

There is a simple recipe for

preventing accidents: see

and be seen. But vision is a

complex process. Road

lighting needs to take ac-

count of that.

Daylight illuminance ranges

from 5,000 to 100,000 lux

(lx). On a moonlit night, it

reaches 0.25 lx at most.

The fact that we can “see”

over this vast brightness

range is due to the eye’s

ability to adapt. At low

adaptation levels, however,

visual performance is im-

paired.

Cones for colour vision,

rods for seeing in the

dark

Visual performance is best

in daylight, when the eye’s

colour-sensitive cone re-

ceptors are active: colours

are easily distinguished,

objects and details clearly

made out. In darkness,

different receptors take

over. These are the rods,

which are fairly insensitive

to colour but highly sensi-

tive to brightness. In the

transitional stage, in twilight,

both receptor groups are

active.

Identification depends on

contrasts

Contrasts are differences in

brightness and colour in

the visual field. To be per-

ceived by the human eye,

they need to be sufficiently

pronounced. The minimum

contrast required for per-

ception depends on the

ambient brightness (adap-

tation luminance): the

brighter the surroundings,

the lower the contrast per-

ceived. In darker surround-

ings, an object needs either

to contrast more sharply or

be larger in order to be

perceived.

Photo 5: As darkness increases,

visual performance deterio-

rates. Road lighting restores

lost performance, enabling

shapes and colours to be ade-

quately made out.

The four basic lighting quantities

Luminous flux ( Φ ) is the rate at which light is

emitted by a lamp. Measured in lumen (lm), it de-

fines the visible light radiating from a light source

in all directions.

Luminous intensity (I) is the amount of luminous

flux radiating in a particular direction. It is mea-

sured in candela (cd). The spatial distribution of

luminous intensity – normally depicted by an inten-

sity distribution curve (IDC) - defines the shape

of the light beam emitted by a luminaire, reflector

lamp or LED.

Illuminance (E) – measured in lux (lx) – is the

luminous flux from a light source falling on a given

surface. Where an area of 1 square metre is uni-

formly illuminated by 1 lumen of luminous flux,

illuminance is 1 lux. The flame of an ordinary

candle, for example, produces around 1 lx at a

distance of 1 m.

Luminance (L) is the brightness of a luminous or

illuminated surface as perceived by the human

eye. Measured in cd/m 2 or cd/cm 2 , it expresses the

intensity of the light emitted or reflected by a sur-

face per unit area.

Photo 6: In daylight, visual

performance is at its peak: the

eye’s colour-sensitive cone re-

ceptors are active, every detail

is perceived vividly “in colour”.

Visual performance

Visual performance is

determined by contrast

sensitivity and visual acuity.

It also depends on the time

in which differences in

brightness, shapes, colours

and details are perceived

(speed of perception). A

person travelling fast has

much less time for this than

a pedestrian.

Visual impairment occurs

when our eyes have too lit-

tle time to adapt to differ-

ences in brightness. Hence

the need for adaptation

zones – e.g. at tunnel en-

trances and exits - to make

for a safe transition be-

tween one luminance level

and the other.

Contrast sensitivity

The ability to perceive dif-

ferences in luminance in

the visual field is called

contrast sensitivity. The

higher the brightness level

(adaptation luminance), the

finer the differences in lu-

minance perceived. Con-

trast sensitivity is reduced

by glare (see Pages 4/5).

Adaptation time

It takes time for the eye to

adapt to different levels of

brightness. The adaptation

process – and thus the

adaptation time – depend

on the luminance at the

beginning and end of any

change in brightness:

adapting from dark to light

takes only seconds, adapt-

ing from light to dark can

take several minutes.

Visual acuity

The eye’s ability to make

out the contours and colour

details of shapes – such as

a traffic obstruction – is

determined by visual acuity.

Visual acuity improves as

adaptation luminance

increases.

Photo 7: Daylight: Optimum

visual performance, good

colour discrimination, objects

and details can be clearly made

out.

Visual performance at any

one time depends on the

state of adaptation: the

more light is available, the

better the visual perfor-

mance.

Photo 8: Road lighting: Shapes

and colours are much harder to

make out but can still be ade-

quately distinguished.

Photo 9: Moonlight: Colour per-

ception is not possible, low-

contrast details are no longer

discernible.

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