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Down on the Street

Issue 53 Feb / Mar 2010

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 of Design and Construction announced the winner of their competition to design and supply an LED street light for the 21st century the rest of the industry has pushed LEDs as a viable alternative solution to more traditional street lamp technologies. Unfortunately, the majority of LED based products have fallen well short of the requirements for this tough application and there are still many commercial and technical challenges to overcome before LED streetlights are truly a like-for-like alternative.

According to Urban Vision Partnership, a joint venture between Salford City Council, Capita Symonds and Morrison Highways Maintenance, there are:
• 7.4 million UK lighting columns;
• 2.32 million of these are over 30 years of age;
• 1.17 million of these are over 40 years of age;
• £64,000 is spent on energy per hour;
• £260 million is the annual energy cost;
• 1.3 million tonnes of carbon emitted per year.
This information shows why there is a great demand for street lighting in the UK as the lighting stock is ageing. The annual energy costs may seem high but it only represents £35 per light fixture per year and this is one of the major barriers to the adoption of LED street lights which have a significantly higher capital cost compared to the equivalent traditional lamp sources such as mercury, metal halide and low pressure sodium lamps.

A typical traditional street lighting fixture will cost £100 but the LED equivalent is currently £250-£300 so if we assume that even the latest LEDs have a lumens per watt efficiency of approximately 100 there will be no real payback for installing an LED fixture as most of the traditional lamp sources are between 100 and 180 lumens per watt efficiency.

Of course, I hear so many LED advocates state that LEDs have many advantages over traditional street light sources such as improved CRI, no restrike issues, longer life and less maintenance issues. But as I will explain, many of these advantages are more reliant on marketing spin rather than practicalities. Therefore, I will attempt to try and dispel a few of the myths of LED street lighting:
Improved Energy Efficiency: LEDs are not as efficient as traditional lamps at high power consumptions and therefore on energy consumption metrics LEDs would not save money.
Long Life: Although LEDs do have improved lifetime characteristics compared to most traditional lamp technologies with most reputable LEDs quoting >60,000 hours, the issue should be more about system lifetime which includes lamp or ballast and driver lifetime. Even though a low pressure sodium lamp offers a lifetime of only 18,000 hours by the time the driver or ballast is taken into account the system lifetime will be equivalent for both traditional and LED systems and so one can easily argue today that there is no advantage to choosing LED streetlights for improved maintenance return on investment.
Reduced maintenance: Many of the LED streetlamp manufacturers state that LED fixtures require less maintenance and so the cost of replacing bulbs can be significantly reduced. In many respects this is correct, however not entirely true as many of the street lamp housings need to be cleaned in order to maintain light output levels and this would still be required for LED fixtures. Often lamp replacement or other maintenance will be undertaken during the cleaning process therefore minimising costs.
Glare: One issue of street lights is the amount of glare given out due to the significant amount of lumens provided in such a small apparent aperture size. LEDs tend to increase the glare aspects of street lights as they use large numbers of high intensity small aperture light sources.    
Head size: LED fixtures are not necessarily smaller than their traditional lamp equivalents and therefore special consideration to the design has to be met to ensure wind loading and weight factors are taken into account. Most LED fixtures use 70-150 1 Watt LEDs which take a significant area and the passive heatsink surface area required to dissipate 70-150W of power will be significant.
Of course there are several advantages of LED street lighting fixtures over traditional equivalents including:
Dimming: LEDs enable street lights to easily dim down the intensity when required thus saving power consumption when using DC/PAM dimming drivers.
Improved control: The use of LEDs enable advanced control technologies to be employed cost-effectively within the street light system including:
- Wireless control: The use of low cost RF wireless control.
- Power Line Control: The use of power line control to communicate between street-lighting fixtures.
- Fixture performance monitoring including fault identification and energy consumption.
- Daylight switching
Reduced Optical Power: The power spectral density of LEDs along with the response of the human eye mean that up to 40% less optical power is required compared to traditional lamps to obtain the same visual appearance meaning LED power or lumen output can be reduced to obtain the same visual appearance.
Higher CRI: LEDs offer higher CRI properties compared to traditionl light sources with a typical range between 65 and 80.  

There are significant challenges for end users to change their street lighting fixture population and these pressures will provide a significant drag on LED adoption:
Vandalism: Significant numbers of lighting columns and fixtures require repairing due to vandalism. Typical damage includes removal of access panels at the base of the lighting column, smashed lighting heads and column damages.
Unrecoverable accident damage: Road traffic damage is usually difficult for Local Authorities to recover costs and therefore take a proportion of maintenance budget.
Inefficient control gear: Old electro magnetic ballasts and old capacitors have a negative effect on energy budgets. Balanced decisions by Local Authority managers need to be made whether they bulk change these old capacitors and if they don’t there is the potential for energy companies to charge more. If they do have a bulk replacement programme, how do they dispose of the old lighting components? Many of them contain PCBs that all pull on scarce resources.
Outdated luminaires: Outdated luminaires fitted with old gear, with no real optical control and outdated light sources are another cost issue. Out of a lamp population of 28 thousand in the Salford area, 43% are Low Pressure Sodium with many fitted with old control gear resulting in high energy usage, low illumination and no colour recognition.
Lack of investment: A few Local Authorities have cash to invest in new infrastructure, or turn to PFI projects to fund capital expenditure. However many Local Authorities are under-funded with resources being diverted to frontline services such as education and social care. These pressures usually mean that street lighting investment is vulnerable which leads to structurally unsound stock. This is a national as well as a local problem.
Stock condition and inventories: Local Authorities should inspect their lighting columns to TR22 and be able to have a detailed age and condition profile. If not it will be very difficult for Local Authorities to bid for funding to renew any ageing stock. Its vitally important therefore that Local Authorities find the resources to keep their inventories up to date not only for stock condition but producing priority lists for schemes and for energy monitoring. Without this information Local Authorities can’t carry out what if scenarios to determine options for reducing energy and maintenance costs.

There is no doubt that LED technology will begin to dominate the street lighting scene over the next decade but in my opinion its adoption will be much slower than most LED companies predict mainly because:
• LED technology is relatively new and still unproven in the application.
• Street lighting engineers will wait until there are proven advantages in real-life applications and not on datasheets.
• There are significant financial constraints on Local Authority budgets due to the economic recession with many predicting annual cuts of between 10 and 20% from the next budget.
• Local Authorities have higher priorities on their agenda such as education and social services which will pressurise residual budgets notionally set aside for lighting.
• Traditional light sources are very efficient for the application and therefore there is less pressure to change the technology until LEDs offer a significant advantage.
• LED street light capital expenditure is two to three times more expensive than current technology and the return on investment is still too long to make investment by Local Authorities attractive.
• Although the lower power street lights could be replaced by LED equivalents today the majority of the traditional street lamps will be more difficult to replace as LED technology has still to mature for higher power applications.

Having stated this there is a clear LED advantage which is the rate of performance increase for LED technologies is significantly higher than traditional lamps and LED costs are decreasing at an equivalently phenomenal rate. Therefore, it is not a question of if LEDs will replace traditional light sources, but when.

Some of the latest LED technologies being introduced offer significant leaps in performance for LED street lighting and will start to offer real alternatives to traditional street lighting fixtures.

Bridgelux, a leader in LED arrays are about to launch the BXRA-C4500 a compact LED array that is ideal for LED street lighting applications having 4500 lumens output when operated at a case temperature of 60C. The new device has a nominal colour temperature of 5600K and a typical colour rendering index of 65 all within an array of 50.3mm x 45.3mm.

The latest Cree XP-G LEDs are also an excellent technology for streetlighting applications as they use larger LED die enabling higher lumen outputs whilst maintaining LED efficacy. The latest XP-G LEDs are capable of delivering 345 lumens at 1A and still achieving 105 lumens per watt efficiency.This has enabled Liaoyuan Lighting, a Chinese lighting manufacturer, to create a street lamp system efficacy of 98.3 lm/W in a 150-watt product.

There will also be a range of new high power LED driver technologies specifically for street lighting applications launched during 2010 that significantly improve lifetime characteristics and provide precise power control, remote placement of drivers away from the LED arrays (resulting in easier maintenance access and low voltages up the lighting column) and intelligent communication protocols. One such company is IST who are launching the iDrive DSP range of drivers to improve the lifetime of LED drivers by employing advanced digital signal processing to monitor voltage, current and total LED array power at up to 100,000 times per second.

There have been several high profile demonstration installations of LED street lighting that have been funded by local, regional or national governments across the world to benchmark the real performance of LEDs in the application.

One such demonstration project was funded by the Department of Energy in the US and they published a report in November 2009 on the installation of LED residential street lighting in Portland, Oregon. This GATEWAY demonstration report provides an overview of project results including lighting performance, economic performance, and potential energy savings (
In this project, eight 100-watt (nominal) high-pressure sodium cobra head fixtures were replaced with LED street light luminaires. Key findings from the study include:
• Estimated payback was approximately 7.6 years for new installations and 20 years for replacement scenarios.
• While measured energy savings were significant at 55%, they were primarily achieved through reducing average illuminance levels by 53%. Illumination now more closely meets the level specified by the city for residential streets.
• Ten of eleven respondents in the resident survey either noticed no difference or thought the lighting quality was improved following the LED substitution.

The results of the study show that energy savings can be made but the savings correspond to a near linear reduction in the average illuminance levels. Therefore, this shows that in practice the system efficiency of LED street lighting in 2009 was roughly equivalent to that of traditional lamps for low power 100W high-pressure sodium lamps. Of course, when higher power street lights are required eg; 200W or 400W sodium-lamp equivalents, the LED street lights will begin to fall significantly short on efficiency performance due to the thermal heating issues of so many LEDs and so there are still significant challenges for LEDs to meet in the foreseeable future.
There are currently several other benchmarking studies being undertaken and so the industry should be able to gain further information of real-life performance of LED street lighting over the next few years.

The interesting point to note when reviewing these studies will be what LEDs they have used in the lighting fixture head because the information being published will be significantly out of date as LED technology is improved on a six to twelve month cycle so most of the reports will be based on last years technology! This is always going to be a challenge for the end-user as they have the very hard decision of whether to opt for the technology today or wait twelve months and adopt much improved technology with higher efficiencies and longer life.
Further studies include those from Ann Arbor city government which have taken a very proactive stance promoting LED usage. The city has created a whitepaper ( and states a goal of cutting the streetlight energy bill in half.

The university’s Mascaro Center for Sustainable Innovation has recently completed a 72-page in-depth study on LED streetlights entitled ‘Life cycle assessment of streetlight technologies’. The report recommends that Pittsburgh replace its 40,000 streetlights with LEDs which would allow the city, which spends $4.2 million annually on electricity and streetlight maintenance, to save $1 million each year in energy costs and $700,000 in maintenance costs with LED lighting.
The report goes on to say that for now, induction lighting holds a slight edge over LED lighting in environmental issues, costs and other factors.
It is clear that LED technology will begin to dominate the street lighting scene over the next decade and 2011 will be the tipping point for mass adoption (rather than trial sites) for LED street lights.
Even with significant improvements in LED performances and a reduction in costs there is only a compelling reason to change to LED streetlights if the current lighting stock is due for replacement. In my opinion it would not be a good use of scarce public resources to replace traditional light source streetlamps that have been replaced in the last decade as there is little or no efficiency gains from using today’s LED products.

I certainly feel that there will be strong merit to convert all street lighting over to LED products in the next decade and its clear that the market will start to accept LED products over the next few years.

Geoff Archenhold is an adviser to the UK Government on LED technology and helps LED companies raise investment from the finance community. He is an investor in an LED driver company and an LED fixture company, a Lighting Energy Consultancy and euroLEDs Events LLP.

The views expressed in this article are entirely those of Geoff Archenhold and not necessarily those of mondo*arc.


Dr Geoff Archenhold
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