104 TECHNOLOGY / STREET & AMENITY LIGHTING 000 TECHNOLOGY / LED PRODUCT
DOWN ON
THE STREET
Dr Geoff Archenhold suggests that the time isn’t quite right for LED street lighting... but it’s not far off
Ever since The New York City Department practicalities. Therefore, I will attempt to
equivalents including:
of Design and Construction announced try and dispel a few of the myths of LED
• Dimming: LEDs enable street lights to
the winner of their competition to design street lighting:
easily dim down the intensity when required
and supply an LED street light for the 21st • Improved Energy Efficiency: LEDs are
thus saving power consumption when using
century the rest of the industry has pushed not as efficient as traditional lamps at
DC/PAM dimming drivers.
LEDs as a viable alternative solution to high power consumptions and therefore on
• Improved control: The use of LEDs
more traditional street lamp technologies. energy consumption metrics LEDs would not
enable advanced control technologies to be
Unfortunately, the majority of LED based save money.
employed cost-effectively within the street
products have fallen well short of the • Long Life: Although LEDs do have
light system including:
requirements for this tough application improved lifetime characteristics compared
- Wireless control: The use of low cost RF
and there are still many commercial and to most traditional lamp technologies with
wireless control.
technical challenges to overcome before most reputable LEDs quoting >60,000 hours,
- Power Line Control: The use of power line
LED streetlights are truly a like-for-like the issue should be more about system
control to communicate between street-
alternative. lifetime which includes lamp or ballast and
lighting fixtures.
According to Urban Vision Partnership, a driver lifetime. Even though a low pressure
- Fixture performance monitoring
joint venture between Salford City Council, sodium lamp offers a lifetime of only 18,000
including fault identification and energy
Capita Symonds and Morrison Highways hours by the time the driver or ballast is
consumption.
Maintenance, there are: taken into account the system lifetime will
- Daylight switching
• 7.4 million UK lighting columns; be equivalent for both traditional and LED
• Reduced Optical Power: The power
• 2.32 million of these are over 30 years of systems and so one can easily argue today
spectral density of LEDs along with the
age; that there is no advantage to choosing LED
response of the human eye mean that up to
• 1.17 million of these are over 40 years of streetlights for improved maintenance
40% less optical power is required compared
age; return on investment.
to traditional lamps to obtain the same
• £64,000 is spent on energy per hour; • Reduced maintenance: Many of the LED
visual appearance meaning LED power or
• £260 million is the annual energy cost; streetlamp manufacturers state that LED
lumen output can be reduced to obtain the
• 1.3 million tonnes of carbon emitted per fixtures require less maintenance and so the
same visual appearance.
year. cost of replacing bulbs can be significantly
• Higher CRI: LEDs offer higher CRI
This information shows why there is a great reduced. In many respects this is correct,
properties compared to traditionl light
demand for street lighting in the UK as the however not entirely true as many of the
sources with a typical range between 65
lighting stock is ageing. The annual energy street lamp housings need to be cleaned
and 80.
costs may seem high but it only represents in order to maintain light output levels
£35 per light fixture per year and this is and this would still be required for LED
CHALLENGES FOR END-USERS
one of the major barriers to the adoption of fixtures. Often lamp replacement or other
There are significant challenges for end
LED street lights which have a significantly maintenance will be undertaken during the
users to change their street lighting fixture
higher capital cost compared to the cleaning process therefore minimising costs.
population and these pressures will provide
equivalent traditional lamp sources such • Glare: One issue of street lights is the
a significant drag on LED adoption:
as mercury, metal halide and low pressure amount of glare given out due to the
• Vandalism: Significant numbers of lighting
sodium lamps. significant amount of lumens provided in
columns and fixtures require repairing due
A typical traditional street lighting fixture such a small apparent aperture size. LEDs
to vandalism. Typical damage includes
will cost £100 but the LED equivalent is tend to increase the glare aspects of street
removal of access panels at the base of the
currently £250-£300 so if we assume that lights as they use large numbers of high
lighting column, smashed lighting heads and
even the latest LEDs have a lumens per intensity small aperture light sources.
column damages.
watt efficiency of approximately 100 there • Head size: LED fixtures are not
• Unrecoverable accident damage: Road
will be no real payback for installing an necessarily smaller than their traditional
traffic damage is usually difficult for Local
LED fixture as most of the traditional lamp lamp equivalents and therefore special
Authorities to recover costs and therefore
sources are between 100 and 180 lumens consideration to the design has to be met to
take a proportion of maintenance budget.
per watt efficiency. ensure wind loading and weight factors are
• Inefficient control gear: Old electro
Of course, I hear so many LED advocates taken into account. Most LED fixtures use
magnetic ballasts and old capacitors have
state that LEDs have many advantages 70-150 1 Watt LEDs which take a significant
a negative effect on energy budgets.
over traditional street light sources such area and the passive heatsink surface area
Balanced decisions by Local Authority
as improved CRI, no restrike issues, longer required to dissipate 70-150W of power will
managers need to be made whether they
life and less maintenance issues. But as I be significant.
bulk change these old capacitors and if
will explain, many of these advantages are Of course there are several advantages of
they don’t there is the potential for energy
more reliant on marketing spin rather than LED street lighting fixtures over traditional
companies to charge more. If they do have
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