WOKINGHAM BOROUGH COUNCIL
STREET LIGHTING UPGRADE PROJECT
Considerations on the Specification of LED Street Lighting
Summary:
1.
We will continue with our practice of providing ‘white’ light as the source for its street
lighting.
2.
We will continue to our practice in specifying LED units that have a “neutral” colour
temperature.
3.
We will continue to install control equipment that facilitates and uses a central
management system (CMS).
4.
We will continue the practice of adjusting lighting levels, i.e. dimming and part-night
lighting, to suit the characteristics of the street and/or local environment.
Drivers:
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To introduce a type of street lighting that better suits the human eye and improves
general visibility and recognition.
To improve the management of lighting levels to be more sympathetic to the local
street scene and surrounding environment.
To reduce energy consumption to minimise the impact on the macro environment.
To reduce local expenditure, thus alleviating the pressure on the Council’s annual
budget and burden on the local tax payer.
To reduce public spending, as required and promoted by Central Government.
Background:
1.
Wokingham currently operates approximately 15,200 ‘highway’ lighting units, 690
non-highway units and the Town and Parish Councils some further 600. The large
majority of these units are lighting residential streets, footpaths and other public open
spaces.
2.
As with most street lighting in England, in recent decades Wokingham have been
predominantly using High-intensity Discharge (HID) lamps, i.e. Low Pressure Sodium
(SOX) as the light source for its residential streets, footpaths and public open spaces
and High Pressure Sodium (SON) for higher trafficked roads and spaces. SOX
provides a very yellow light (colour temperature of 1800K) and SON a light which is
somewhat whiter but still yellow (colour temperature of 1900K to 2000K).
3.
The human eye has developed to be as efficient as possible utilising sunlight and
moonlight, which are white light. Artificial white light therefore provides clearer vision
with improved colour rendition (see Annex 1) and facial recognition and is therefore
regarding as being a better and more suitable/natural light source than SOX and/or
SON. In the mid 2000’s Philips developed a new type of HID lamp that was more
energy efficient and provided a ‘whiter’ light (colour temperature of 2800K).
Wokingham therefore took the decision to move to ‘white’ street lighting and started
to introduce this new lamp in 2010.
4.
During a similar period, Light Emitting Diode (LED) technology was also being
developed. The benefits of LED’s are that they can produce a white light using far
less energy. LED’s can now be provided in a range of light temperatures from ‘warm’
(colour temperature <3000K) to ‘cool’ (colour temperature >5000K). When LED
lanterns, providing an acceptable light output, became more widely available from
various manufacturers, and a cost effective alternative to the previously used Highintensity Discharge lamps, Wokingham started to introduce LED lighting units as part
of its maintenance and column replacement programmes in 2012.
Considerations:
1.
In relative terms, regarding the development of our species and society, the
introduction of affective street and other external lighting is a very modern
occurrence, with its first introduction in the late 1700’s using gas. Prior to this we
would have relied on the various forms of ‘fire’ light. With the growth in population,
the expanding industrial/commercial environment and the development of private
motor vehicles, the extent of street lighting provision increased dramatically as the
last century progressed. It has now become more and more a public expectation for
the urban environment to be lit. The primary driving forces for this being the fear of
crime, road safety, life style and commercial growth with the aim of prolonging the
length of the productive ‘day’.
2.
To a great extent this is being achieved but, at the same time, has resulted in higher
and higher energy use, with its adverse effects on the macro environment, and a
proportional increase in the financial burden on the public purse, neither of which are
now considered sustainable. To address and balance the conflicting demands, new
technologies has been regularly developed, improved and introduced to increase
output performance, i.e. gas, electric incandescent lamps up to the 1950’s, the
introduction of HID lamps and more recently LED’s.
3.
A further consideration that should be taken into account in providing street lighting is
the affects it has, or may have, on communities, individuals and other fauna and flora
that inhabit the local environment. It is likely that this has not been a major factor in
the past but have been accepted as necessary consequences. However, with the
introduction of LED’s and other systems, these can now be addressed to some
degree. Without delving too deeply into the technicalities, there are three main areas
that need to be taken into account, i.e. how eyes have developed and work, the type
of light being provided and how the light is managed.
4.
From the formation of the Earth, until relatively recently, the only source of
illumination has been the ‘white’ light produced directly from the sun or reflected via
the moon. Eyes have developed, to a lesser or greater extent, to take advantage of
this type of light and it provides the best type of light for vision. SON and, to an even
greater extent, SOX do not provide good vision characteristics, being ‘yellow’ light,
and tend to be of a high intensity/brightness to compensate. Given that white light
enables better vision, the Street Lighting Upgrade Project will continue with
our practice of providing ‘white’ light as the source for its street lighting.
5.
The original LED’s produced a cool white light that have a colour temperature tending
towards sunlight (>5000K) but more recently, warmer whites have been made
available. Cool white is perceived to be quite ‘harsh’ and previous installations have
been the subject of comments regarding the level of brightness/glare and possible
effects on wellbeing. Warm white may reduce these affects and is therefore being
favoured in city centres and other urban areas where a high uniformity of lighting is
consider necessary and/or there are high levels of pedestrian use/leisure activities.
However, warm light LED’s produce at least 10% less lumens (light) for the same
power input and provide a slightly reduced vision quality, which is compensated for
by higher lighting levels and uniformity. The nature of the majority of Wokingham’s
street scene does not have a high enough footfall to warrant city centre levels of
uniformity and much of it is of a rural/residential nature with low uniformity. It is
therefore more important, in Wokingham’s case, to provide lighting that favours better
vision characteristics. On the whole, LED units operate at a lower “brightness”
(measured in Kilo Lumens) than SOX and SON lamps (see Annex 1), although this is
not always the perception.
6.
It is also the case that species have existed in conjunction with the natural rhythms of
day and night, which best suited their development. However, since the discovery
and use of fire, humans have been challenging this natural cycle and introduced
artificial light in order to extend their day to become safer and more productive.
Within our buildings and homes we are able to control the levels of lighting to
coincide with our work or domestic needs and to be able to “switch it off” to align with
our natural/chosen circadian rhythms. This, however, is not tend to be the case with
most street lighting.
7.
Traditionally street lighting is set at a generic level for the volume of traffic and is
switched on and off automatically by photocells, triggered by the level of daylight.
This means that the lighting operates at the same brightness, all night long and takes
little account of the street and adjacent property layouts. Most households have
become familiar and accustom to dealing with the yellow light produced by SOX/SON
lamps However, light intrusion can still occur due to the poor optics of “old” lantern
designs that give a less focused light spread than new lantern designs. There is
growing research and evidence that indicates that the use of “cool” light (>5000K),
that is akin the sunlight, can have a greater effect on our natural/chosen circadian
rhythms. It is therefore important to take this into account with the choice of a new
light source. The Council’s technical officers, together with a specialist lighting
consultant, had previously considered these factors and balanced the technical
aspects with economic pressures and environmental concerns to specify and install a
“neutral” colour temperature of 4000K. This has a similar colour temperature to
moonlight (See Annex 2), but its colour spectrum has a higher “blue” content than
moonlight. The Street Lighting Upgrade Project will continue our practice in
specifying LED’s that have a “neutral” colour temperature.
8.
The “all night long” and “one size fits all” approach to street lighting is the result of the
technologies that have been available, with lanterns requiring pre-set hardware to
control switching and power. Any change to the pre-set controls would require each
individual lantern to be visited and replacement hardware installed. This does not
lend itself to a particularly flexible approach. This situation has recently changed with
the introduction of central management systems (CMS) that utilise two way, low
frequency, radio communications linking individual lanterns to a central computer
programme. This allows real-time monitoring information to be sent from a lantern to
the maintenance engineers - lantern performance, faults and energy consumption
being examples. The system will also allow engineers to initially set individual lantern
lighting level and switching regime and, if required, adjust these without having to
make a visit to the units and or replace equipment.
9.
The installation of a central management system therefore enables a far more
flexible/corrective approach to be taken in setting lighting levels and responding to
customer contacts. This ability, coupled with improved lantern optics and shields, can
mitigate over lighting and reduce the level of light intrusion/disturbance to adjacent
properties. The Street Lighting Upgrade Project will continue to install control
equipment that facilitates and uses a central management system (CMS).
10. A central management system can also be used to adjust lighting levels and switching
times on a day to day basis. Wokingham have already introduced a regime of dimming
its street lighting and, at suitable locations, switch them off for a proportion of the
darkness hours. This can assist and further improve the mitigation the non-visual
effects of light intrusion/disturbance and has the added benefit of reducing energy
consumption/costs still further. Information about part-night lighting can be found on our
website. The Street Lighting Upgrade Project, will continue the practice of
adjusting lighting levels, i.e. dimming and part-night lighting, to suit the
characteristics of the street and/or local environment.
Annex 1
Comparison of LED v Discharge Lamps
Existing SOX
Column
Height
Existing SON
Existing
Watts*
Luminous
Flux
(Lumens)
Colour
Temp
(Kelvin)
Colour
Rendering
Index (RI)
Existing
Watts*
Luminous
Flux
(Lumens)
5m
35w
4550-4700
1800
n/a
50w
3500-4400
6m
55w
7800-8000
1800
n/a
70w
5600-6600
8m
90w
13600
1800
n/a
100w
10m
135w
22600
1800
n/a
150w
12m
180w
3200
1800
n/a
250w
900010700
1500017700
2800033000
Existing CPO/CDM
Colour
Rendering
Index (RI)
Existing
Watts*
Luminous
Flux
(Lumens)
Colour
Temp
Colour
Rendering
Index (RI)
25
45w
4650
2800
65
25
60w
7090
2800
70
2000
25
90w
10000
2800
63-66
2000
25
140w
16800
2800
68
2000
25
210w
2200024150
29404200
90
Colour
Temp
19002000
19002000
Proposed LED
Column
Height
"Typical"
Proposed
Watts*
"Typical"
Luminous
Flux
(Lumens)†
Colour
Temperature
Colour
Rendering
Index (RI)
5m
6m
8m
10m
12m
17w
24w
61w
81w
166w
2000
3000
8800
12000
24000
4000
4000
4000
4000
4000
>70
>70
>70
>70
>70
Notes:
*Wattage stated is "Nominal" Wattage of lamp not "Circuit" Wattage or dimmed wattage
†LED info based on Philips LED's currently in use by WBC. Maximum lumen output and wattages of the proposed LED's may be increased or decreased and will be
varied according to site through permanent dimming control but generally will be similar to that shown.
Annex 2
Colour Temperatures:
Temperature
Source
1,700 K
Match flame, low pressure sodium lamps (LPS/SOX)
1,850 K
Candle flame, sunset/sunrise
2,400 K
Standard Incandescent lamps
2,550 K
Soft White Incandescent lamps
2,700 K
"Soft White" compact fluorescent and LED lamps
3,000 K
Warm White compact fluorescent and LED lamps
3,200 K
Studio lamps, photofloods, etc.
3,350 K
Studio "CP" light
4,100–4,150 K
Moonlight[2]
5,000 K
Horizon daylight
Tubular fluorescent lamps or
5,000 K
cool white/daylight compact fluorescent lamps (CFL)
5,500–6,000 K
Vertical daylight, electronic flash
6,200 K
Xenon short-arc lamp[3]
6,500 K
Daylight, overcast
6,500–9,500 K
LCD or CRT screen
15,000–27,000 K Clear blue poleward sky
These temperatures are merely characteristic and could vary.