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Learning Center

Useful Links

http://www.lrc.rpi.edu/programs/solidstate/  - Lighting Research Center
http://www.iesna.org/   - Illuminating engineering society
http://www.darksky.org – International dark sky association
http://www.ledsmagazine.com/ - LEDs Magazine, the leading global information source for the LED lighting market.
http://light-building.messefrankfurt.com/frankfurt/en/besucher/willkommen.html - Light Building, leading fair in lighting industry
http://www.strategiesinlight.com/index.html  - Strategies in light, leading events for the global LED and lighting industry
http://www.sileurope.com/index.html - Strategies in Light, Europe

http://www.sdr.si – Lighting society of Slovenija
http://www.sloluks.si – Lighting institute and light planner


Frequently asked questions

    What is an LED light?
    In what stage is the development of LED technology today?
    In what kind of applications are LEDs used?
    Can LED street lights efficiently replace HID lamps?
    Is it possible to just replace an old bulb with an LED bulb and not with the whole LED luminaire?
    How can I differ between low quality and high quality LED luminaire?
    Where can the LED street lights be seen?
    What is the investment cost of LED street luminaires compared to other technologies?
    What are the main disadvantages of LED technology?
    What is the lifetime of LED luminaires?
    Is there a warm-up time needed when switching on a LED luminaire?
    How mechanically durable is a LED luminaire?
    How accurate is the color reproduction of LED light?
    Can LEDs be dimmed?
    Does dimming LEDs decrease their lamp life?
    What does the IP and IK rating means
    Do LED luminaires contain any harmful substances?
    Is there any infrared radiation coming out of LED luminaires?
    How is white ultraviolet radiation in LED luminaires?
    How much can I save with LSL® lights?


What is an LED light?

An LED light is a solid-state lamp that uses light-emitting diodes (LEDs) as the source of light. It is a small electronic device (a semiconductor diode) that emits light when electricity passes through it. It is one of the most efficient and prosperous light sources available on the world market. According to the latest research and further development advances of the LED industry, LED light technologies will be the leading lighting force in the future.

In what stage is the development of LED technology today?

LEDs are dramatically increasing light output, efficiency, reliability and are becoming increasingly more brighter. The lumen output of LEDs has almost doubled in the last two years. At the end of 2009 the LED technology was mature enough to enter the high demanding market of outdoor illumination and to successfully compete with existing street lighting technologies.

In what kind of applications tare LEDs used?

LED technology has been used for several decades in various applications. White LED lamps have achieved market dominance in applications where high efficiency is important at low power levels. Some of these applications include flashlights, solar-powered garden or walkway lights, and bicycle lights. Monochromatic (colored) LED lamps are now commercially used for traffic signal lamps, where the ability to emit bright monochromatic light is a desired feature, and in strings of holiday lights. LEDs are widely used in automotive industry, military and yachting lighting. Its use in domestic electronic appliances and high tech devices is rising. LED lights have also become very popular in gardening and agriculture by 2010. First used by NASA to grow plants in space, LEDs came into use for home and commercial applications for indoor horticulture (aka grow lights).
The incredible rapid progress of LED technology in the last few years enabled LEDs to become appropriate for use in general and outdoor lighting applications. Latest LED technologies used in LED luminaires are not only satisfying the needs of quality outdoor and general illumination but are already exceeding all other technologies in all parameters.

Can LED street lights efficiently replace HID lamps?

Yes, LED street lights can efficiently replace and outperform HID lamps with numerous advantages (long lifetime, directional light distribution, high light unformity, no maintenance, durability, high color rendering index, etc.). All this without emissions that would be harmful to the environment.

Is it possible to just replace an old bulb with LED bulb not with the whole LED luminaire?

Some manufacturers are even producing LED bulbs, but the fact is that even if an LED bulb fits into an existing luminaire, the overall lighting output and performance cannot cope with the LED luminaire. The housing of LED luminaire is designed especially for the needs of LEDs to maximize its efficiency, performance and life-time. On the other hand traditional housing doesn´t offer the optimized working condition, especially not from the thermal management point of view.

How can I differ between low quality and high quality LED luminaire?

While choosing the right LED solution, you have to be aware, that LED technology has progressed rapidly in the past few years, that not all LED luminaires are created equal and that some manufacturers are offering extremely low cost options, which are inferior and of poor quality. To be really sure that technical claims of the manufacturer are true, you have to inspect and test the product carefully. Only the technical characteristic of an LED cannot define the performance of an LED luminaire, since the system is composed from many critical components (like optics, thermal management, driver etc.) which are the key to optimized overall performance and efficiency.
You can recognize some low quality LED solutions by some common characteristics:

unpleasant pale blue shine of light (color temperature 5.500 K and more) open casings and visible cooling ribs that indicate weakly solved problem of light heating (accumulating dirt on cooling ribs mean more maintenance cost, while openings in casing cause malfunction of electronics and reduced life expectancy) low quality components (optics, LEDs, driver, etc.) assembled together in manufacture with lack of technical expertise and quality control can cause uneven distribution of light beam, poor light and energy efficiency, glare etc., etc.

Always be sure that the manufacturer technical claims are not misleading but are verified with valid, acceptable and verifiable certificates. Also be sure that the manufacture has a stolid, reliable background/history and can fulfill its warranty claims together with full customer support.

Where can the LED street lights be seen?

LED street lights have been installed or announced for installation in several large cities as well as smaller cities throughout the world (Boston, Worcester, Cleveland, Varna, Toronto, New York, Budapest, Los Angeles,…). Also a number of reports on the results of pilot projects for municipal outdoor lighting are available. Most of the cities that are following the policy of »green cities« have implemented LED technology in their future city development.

What is the investment cost of LED street luminaires compared to other technologies?

The cost of LED street luminaire is higher than that of other technologies, but when considering all the benefits and cost savings you will acquire with the right LED solution, there is no other serious alternative. Due to high energy efficieny your electricity bills will be drastically reduced, you will have no maintenance cost, you will lower your carbon emission and most important you will enjoy these benefits for decades, while return on investment will be realized in less than 2 years in most cases. With a solid financial plan your cash outlay will be minimal and with the realized savings may not cost anything at all compared to what you are utilizing at the present time.

What are the main disadvantages of LED technology?

The biggest disadvantage of LED technology is lack of education and knowledge about the technology itself and lots of poor quality solutions available on the market. There is a lot of misleading information on the market, coming from two main sources:

manufacturers with low quality solutions, which are misleading the consumer withfalse technical characteristics and claims
competitors which sell inefficient lighting technologies, which will soon be banned, so they can deplete existing inventories.

There are also a number of companies who claim to be original manufacturers but instead buy inferior quality LED luminaires from countries which mass produce the product, put their own brand on products, change origin and then sell to unsuspecting customers for a higher price.

Some street lighting tests were made while using old immature LED technology before the year 2009 when LED technology was mature enough to seriously compete with other street lighting technologies. Results of these studies are not showing the real condition of LED street light technology today.

The result of all this confusion and organized chaos, is that the crrent market is experiencing unjustified doubt about the LED technology that is currently on the market. Who do you believe ? For the customer this is an extremely valid question. The weakness is not in technology but in cheap quality products and lack of knowledge.
Customers should always be careful and choose only verified high quality LED street light solutions from reputable manufacturers with solid backgrounds and proven history. While checking street lighting tests and reviews, you should always check which product was reviewed and from which year the product is available to avoid possible wrong conclusions.

What is the lifetime of LED luminaires?

LEDs do not burn out like incadescent light bulbs. Instead LEDs over their lifetime  simply get progressively dimmer until they do not emit enough light to be useful. LED is considered to be no longer useful when it is emitting only 70% of the amount of light that it originally emitted. The time when 30% of lumen depreciation occurs is considered to be the "lifetime" of an LED.

High quality LED luminaires can go up to 100.000 hours under good working conditions. The officialy acknowledged standard for life time of high quality LED luminaires worldwide is 50.000 hours. They are still working after that time and can go up to 100.000 hours but with lower lumen output. 100.000 working hours means a lifetime between 11 and 34 years depending on how long a LED luminaire is working every day.


faq 01
faq 02
Is there a warm-up time needed when switching on a LED luminaire?

No. LEDs do not have the long warm-up times, which many people find annoying about CFLs (compact fluorescent lamps). Instead, the light from LEDs shines at full brilliance as soon as the switch is turned on. Also cold temperatures do not affect the performance of LED luminaire.

How mechanically durable is a LED luminaire?

Unlike other light bulbs that use fragile filaments (especially incandescent light bulbs) LEDs are vibration and shock resistant. While vibration or shock easily breaks the fragile filament in an incandescent bulb and the glass tubing of a fluorescent lamp, LEDs tolerate vibration exceptionally well because they do not use filaments. Energized components of the LED are well separated from the outer surface with high quality insulation. The electrodes are embedded in the bulb matrix and the driver electronics are encased in its shell. A layer of interface material between the LED and the heat sink ensures that no current can leak to the heat sink. This make LED luminaire a completely solid-state technology which are virtually indestructible under normal circumstances.

How accurate is the color reproduction of LED light?

Color Rendering Index or CRI is the calculated rendered color of an object. The higher the CRI (based upon a 0-100 scale), the more natural the colors appear. Natural outdoor light has a CRI of 100. White LEDs offer the industry's highest CRI (80-90), making objects to be illuminated appear more natural and vibrant, which increases overall safety.

Can LEDs be dimmed?

The forward current is proportional to the light output of an LED over a large operating range, so dimming can be achieved with reductions in the forward current. Because LEDs can be rapidly switched on and off with no harmfull effects, dimming can be accomplished using a method called pulse width modulation. By adjusting the relative duration of the pulse and the time between pulses, the apparent intensity of the LED can be dimmed. This is done with direct digital control, which enables frequency high enough that LED appears to be continuosly lighted without flickering.

Does dimming LEDs decrease their lamp life?

It has been observed that when some fluorescent lighting systems are frequently dimmed, they might exhibit reliability and lamp life. This is not the case for LEDs. Life and light output degradation are determined largely by the junction temperature, with higher temperatures resulting in reduced life characteristics. Since dimming, either by reducing current or by pulse width modulation, results in lower overall junction temperatures, it will have no negative impact on LED life, it might even extend life.

What does the IP and IK rating means?

IK – protection against mechanical impacts
The European standard EN 62262 ( the equivalent of international standard IEC 62262:2002) relates to IK ratings. This is an international numeric classification for the degrees of protection provided by enclosures for electrical equipment against external mechanical impacts. It provides a means of specifying the capacity of an enclosure to protect its contents from external impacts.

EN 62262 specifies the way enclosures should be mounted when tests are carried out, the atmospheric conditions that should prevail, the number of impacts (5) and their (even) distribution, and the size, style, material, dimensions etc. of the various types of hammer designed to produce the energy levels required.
faq 03
IP – Ingress Protection Rating

The IP Code (or International Protection Rating, also interpreted as Ingress Protection Rating) consists of the letters IP followed by two digits and an optional letter. As defined in international standard IEC 60529, it classifies the degrees of protection provided against the intrusion of solid objects (including body parts like hands and fingers), dust, accidental contact, and water in electrical enclosures The digits (characteristic numerals) indicate conformity with the conditions summarized in the tables below. Where there is no protection rating with regard to one of the criteria, the digit is replaced with the letter X.

IP First number - Protection against solid objects

faq 04

IP Second number - Protection against liquids

faq 05

Do LED luminaires contain any harmful substances?

No, LEDs contain no harmful substances. Mercury is not used in LEDs, frelieving you from the environmental hazards which are present with disposing of burnt-out fluorescent, metal halide, and high pressure sodium light bulbs.

Is there any infrared radiation coming out of LED luminaires?

White LEDs do not emit infrared radiation (no beam heat) so, the beam of light produced by a white LED does not contain any heat. This makes LEDs ideal for shallow ceiling downlighting and display lighting.

How is white ultraviolet radiation in LED luminaires?

White LEDs do not produce any ultraviolet (UV) light even though all other natural and artificial light sources do. This has many benefits:

    Limited Fabric Fading
    When using white LED light fixtures, there will be minimal fading and deterioration of fabrics, documents, or artwork due to exposure to the white light from LEDs.

    Better for Fruits & Vegetables
    Unlike light sources like metal halide, LEDs do not radiate high levels of UV rays. While it is common knowledge that heat can speed up food’s spoilage rate, it is lesser known that high UV levels can actually decrease the nutrient levels in food. Thus, using LEDs to light the produce in a super market, for example, may not only be energy efficient, it may also help the produce to maintain higher nutrient levels.

    Do Not Attract Bugs
    Since white LEDs do not emit ultraviolet light (the invisible portion of the spectrum just beyond visible violet) light fixtures using white LEDs do not attract bugs.

How much can I save with LSL® lights

Savings while replacing inefficient old lamps with Aerolite LSL® LED lights vary depending on wattage and lifetime of currently installed lights. Since LSL® has a minimum lifetime of 60.000 hours (and can easily go up to 100.000 hours), has low wattage and requires almost no maintenance, total savings in electricity and maintenance can be up to 90% compared to old lights. All this can be achieved while improving illumination performance at the same time. Also CO2 emissions will be drastically reduced and considering the fact that LSL® is completely environmentally friendly, by deciding for Aerolite LSL® you will contribute to the protection of the environment.


Replacement of 30 pieces HPS lights to Aerolite LSL®30 lights
18.450 EUR total savings
37.170 kg total CO2 emission reduction

Replacement of 100 pieces HPS lights to Aerolite LSL®90 lights
117.300 EUR total savings
453.120 kg total CO2 emission reduction

Replacement of 500 pieces HMQ lights to Aerolite LSL®30 lights
508.500 EUR total savings
1.805.400 kg total CO2 emission reduction

Replacement of 1000 pieces HMQ lights to Aerolite LSL®90 lights
5.073.000 EUR total savings
27.541.200 kg total CO2 emission reduction

Replacement of 2000 pieces HMQ lights to Aerolite LSL®
30 lights3.390.000 EUR total savings
15.222.000 kg total CO2 emission reduction

Replacement of 200 pieces mercury lights to Titanium LCL®90 lights
741.000 EUR total savings
4.000.200 kg total CO2 emission reduction

Financial Instruments

There are many ways of financing a street lighting project depending on sector :

Consumers :

    Utility funding (over energy bill)
    Private financing (cash settlement, leasing)

Business :

    Energy Service Companies (ESCO models)
    Public Financing Initiatives
    Investors (building certification, cash settlement, leasing)

Government :

    Public Private Partnerships
    Carbon trading
    Revolving renovation funds

Third party financing

An Energy Service Company (ESCO) contracts with the municipality to plan, finance and install energy efficiency technologies at the ESCO's expense. The contract provides that the ESCO is repaid through a share in the value of the energy savings that result from the technology installed. The ESCO offers a total service package, runs and maintains the installation, which results in further savings for the municipality.

The ESCO guarantees the municipality energy savings at a specific amount. Duration of the contracting is usually 10 to 15 years.  For the municipality, there is no or little investment (depending on measures) necessary. It is suitable for projects with highly energy efficient measures, since the savings in energy costs have to pay for the investment of the installation and the ESCO as well. Energy agencies advise municipalities on the way of financing that is suitable for a street lighting project. They develop a financial model, which is part of the analysis preparing the project and do the tendering of the ESCO-project, which ensures a successful realization.


Lease financing is based upon the fact that a municipality uses a property instead of buying it. A properly constructed lease is not considered a public debt. "Lease-purchase" agreements (in which the municipality leases a facility while purchasing it) and "sale-leaseback" agreements (in
which the municipality sells a facility to a lessor and then immediately leases it back) offer several advantages over other financing methods.

A municipality can obtain a facility without a large initial investment. The municipality can obtain quick cash for a facility (although the cost of repaying the lease will exceed the sale price). A lease can be used to spread the cost of a facility over a long period of time. There is also a combination of leasing and third party financing. Using lease financing is not without its drawbacks. The agreements necessary are complicated and expensive and therefore are suited for bigger investments. The municipality is still responsible for design, implementation and maintenance of the street lighting.


Street lighting impact on environment, animal life

Studies in Europe have demonstrated that streetlighting has a significant effect on the mood of human beings, animal life and the environment. It affects navigation of birds and insects, mating behavior in animals and flowering in plants. Millions of insects are attracted to street lights at night (particularly during summer months) and perish. These insects can be an urban nuisance besides adding to the cost of cleaning up lamp fixtures and the street sidewalk to remove dead insects. But not all street lights attract insects or affect animal life the same. The impact of LED lights on animals is much smaller compared to other lights.
studies 01
Light pollution and glare in street lighting

IESNA classifies luminaires as »non cutoff«, »semi cutoff«, »cutoff« and »full cutoff«, depending on how much of light is dispersed above the horizontal line of luminaire.

studies 02

The non-cutoff fixtures usually include the globe-shaped lamps that are mounted on top of lampposts. These lamps distribute their light in all directions. A major problem is created by the light pollution and glare, as they shoot their light upwards into trees and towards the sky rather than down towards the ground. Non-cutoff fixtures are rarely found on roadways because they tend to blind the driver.


This is the most popular street lighting optic. The semicutoff fixtures usually refer to the cobraheads, but they can also apply to some lamppost-mounted fixtures that do not emit their light upwards. Most of the light can be emitted below 90 degrees, but as much as 5% of the light can also be emitted above 90 degrees. These fixtures do a very good job of spreading the light towards the ground but some uplight is possible, though not as serious as non-cutoff fixtures. Semicutoff fixtures are often mounted on tall poles.


These optics give more light control than semicutoffs. Less than 2.5% of the light can leave the fixture above 90 degrees. Cutoff fixtures have gained popularity in recent years, as they are available from manufacturers like GE and American Electric. The cutoff lights have a wider spread of light than full-cutoffs, and they generate less glare than semicutoffs. The cutoff lenses consist of a shallow curved glass (also called a sag lens) that is visible just below the lighting area on the fixture.


These lights do not allow any of the light to escape the fixture above 90 degrees. Full-cutoffs distribute their light in a defined pattern, potentially providing more light on the ground at lower power consumption. Full cutoff means luminaires which are totally environmentally friendly (causing no light pollution).

studies 03 

Photopic and scotopic vision

Scotopic vision: Seeing is believing.

Human vision is enabled by three primary modes:

Photopic vision:
Vision under well-lit conditions, which provides for color perception, and which functions primarily due to cone cells in the eye.

Mesopic vision:
A combination of photopic vision and scotopic vision in low lighting, which functions due to a combination of rod and cone cells in the eye.

Scotopic vision:
Monochromatic vision in very low light, which functions primarily due to rod cells in the eye.

Although all three modes of vision help us see under different conditions, nighttime vision is generally dominated by scotopic mechanisms (for very dark conditions with no ambient light) or mesopic mechanisms (for semi-dark conditions, such as a full moon and heavily lit commercial roadways). Unfortunately, virtually all photometric tests used to determine light output from street lighting sources are based on photopic vision, which is not representative of the human response to light under low light (nighttime) conditions. Photopic measurements favor “warmer” light, such as the orange light produced by common HID street light sources, including high pressure sodium lamps. Scotopic and mesopic measurements are more representative of a broader spectrum of light, including the “cooler” light generated by most LEDs used in street lighting applications.Because of these differences, many leading scientists and lighting experts believe that photopic measurements should be used for daytime and indoor lighting measurements, and scotopic or mesopic measurements should be used to evaluate nighttime lighting measurements.

The Illuminating Engineering Society of North America (IESNA)—which currently uses photopic measurement criteria for evaluating street lights—is currently reviewing the photopic versus scotopic/mesopic measurement issue, and revised street light standards are expected to be issued from the IESNA in the near future. In the meantime, many LED users are evaluating light output based using both photopic and scotopic measurements. Since most photometry is based on photopic measurements, a scientific conversion factor is used to create scotopic measurements from photopic measurement data. These conversions are described in groundbreaking research on this topic conducted by Drs. Sam Berman and Don Jewett.

To convert from photopic to scotopic measurements, simply multiply the photopic measurement for the light source in question by the appropriate factor in the table below:
For example, a 50-watt high pressure sodium light source with 4,000 initial photopic lumens provides only 2,480 initial scotopic lumens based on the 0.62 conversion factor highlighted in the chart above. However, a typical 4,100K light source (typically used in LED street lighting) with the identical 4,000 initial photopic lumens provides 6,642 initial scotopic lumens based on the 1.62 conversion factor highlighted in the chart above. studies 04


Regulations in EU and USA

European Commission issued the Regulations EC No. 245/2009 for tertiary lighting products on 18 March 2009. On the basis of these Regulations, about 1 billion lighting products have to be replaced by the year 2015 only in the area of the EU, which translates to 100 million street lamps for street lighting and industry. The remaining 900 million refer to neon lamps.

Similarly, the Energy Information and Security Act of 2007 began the process of restricting the sale of inefficient lamps in the US. By 2012, with a few exceptions, the result of the legislation will be that inefficient incandescent lamps cannot be sold.

LED lighting market in EU
directives 01
Market overview
directives 02

Street lighting technology comparison

Today, street lighting commonly uses high-intensity discharge lamps, often HPS high pressure sodium lamps. Such lamps provide the greatest amount of photopic illumination for the least consumption of electricity. However when scotopic/photopic light calculations are used, it can been seen how inappropriate HPS lamps are for night lighting. White light sources have been shown to double driver peripheral vision and increase driver brake reaction time at least 25%. When S/P light calculations are used, HPS lamp performance needs to be reduced by a minimum value of 75%.

A study comparing metal halide and high-pressure sodium lamps showed that at equal photopic light levels, a street scene illuminated at night by a metal halide lighting system was reliably seen as brighter and safer than the same scene illuminated by a high pressure sodium system.

New street lighting technologies, such as induction or LED lights, emit a white light that provides high levels of scotopic lumens allowing street lights with lower wattages and lower photopic lumens to replace existing street lights. Formal specifications around Photopic/Scotopic adjustments for different types of light sources enables municipalities and street departments to test, implement and benefit from this new technologies.

Read more about Photopic and scotopic vision here.

Incandescent lamps

Incandescent Lamps are “standard” electric light bulbs that were introduced more than 125 years ago by Thomas Edison. They have the lowest initial cost, good color rendering and are notoriously inefficient. They typically have short life spans and use significantly more watts than CFLs and halogen lamps do to produce the same lumens, or light output. Incandescent technology produces light by heating up a metal filament enclosed within the lamp’s glass.

More than ninety percent of the energy used by an incandescent light bulb escapes as heat, with less than 10% producing light. Their use is most common in areas prone to frequent theft or vandalism of light fixtures. In these locations a very high rate of replacement may make a case for use of these cheap light bulbs. Anywhere else they are too wasteful to make sense. After all, 5 % efficiency and a few hundred hours lifespan are difficult to consider when replacement with LED systems use 7 times less energy.

High Intensity Discharge (HID) Lamps include:

    Mercury Vapor lamps (outdated and almost extinct)
    Metal Halide lamps
    High Pressure Sodium lamps (HPS)

Mercury Vapor Lamps

Mercury Vapor Lamps were introduced in 1948. It was deemed a major improvement over the incandescent light bulb, and shone much brighter than incandescent or fluorescent lights. Initially people disliked them because their bluish-green light. Other disadvantages are that a significant portion of their light output is ultraviolet, and they "depreciate"; that is, they get steadily dimmer and dimmer with age while using the same amount of energy.

Mercury lamps developed in the mid 1960s were coated with a special material made of phosphors inside the bulb to help correct the lack of orange/red light from mercury vapor lamps (increasing the color rendering index(CRI)). The UV light excites the phosphor, producing a more "white" light. These are known as "color corrected" lamps. Most go by the "DX" designation on the lamp and have a white appearance to the bulb. As of 2008, the sale of new mercury vapor streetlights and ballasts was banned in the United States by the Energy Policy Act of 2005, although the sale of new bulbs for existing fixtures do continue.

Metal Halide Lamps

In recent years, metal halide lamp (MH) streetlights have illuminated roadways, parking lots and also warehouses, schools, hospitals and office buildings. Unlike the old mercury lights, metal halide casts a true white light. It is not nearly as popular as its sodium counterparts, as it is newer and less efficient than sodium. MH lamps operate at high temperatures and pressures, emit UV light and need special fixtures to minimize risk of injury or accidental fire in the event of a so called ‘non passive failure’ – or when the lamp bursts at the end of the useful life. A small fire at the Harvard University greenhouse was started by one such lamp that was not properly contained. These cannot start up at full brightness as the gases in the lamp take time to heat up.

Additionally, every time the light is switched on a re-strike time of 5 to 10 minutes is needed before the lamp can be switched on. These lamps are thus not suited to situations when intelligent control systems are used to switch lights on and off. MH lamps suffer color shift as they age though this has been improving. Actual life expectancy is about 10,000 to 12,000 hours on average.The mercury and lead content of these lamps is also a serious issue. A single 1500 watt lamp may contain as much as 1000 mg of mercury. High cost and low life hours has kept them from becoming popular municipal lighting sources even though they have a much improved CRI around 85.

High Pressure Sodium (HPS) lamps

HPS lamps were introduced around 1970 and are one of the more popular street lighting options, the most efficient light source when compared to mercury vapor and metal halide lamps (on a ‘lumen/ watt’ scale). The disadvantage is that they produce narrow spectrum light mostly a sickly yellow in color. These lights have a very low color rendering Index and do not reproduce colors faithfully. These lights do not find favor with police departments as it is difficult to determine the color of clothes and vehicles of suspects from eye witness accounts in the event of a crime. Color-corrected sodium vapor lamps exist but are expensive. These "color corrected" HPS lamps have lower life and are less efficient.

There are two types of sodium vapor streetlights: high-pressure (HPS) and low-pressure (LPS). Of the two, HPS is the more-commonly used type. Low Pressure Sodium lights are even more efficient than HPS, but produce only a single wavelength of yellow light, resulting in a Color Rendering Index of zero, meaning colors cannot be differentiated. LPS lamp tubes are also significantly longer with a less intense light output than HPS tubes, so they are suited for low mounting height applications, such as under bridge decks and inside tunnels, where the limited light control is less of a liability and the glare of an intense HPS lamp could be objectionable.

Another issue of HPS lights is that they contain 1 to 22 mg of mercury for a 100 watt bulb with an average of 16 mg per bulb. They also contain lead. Unsafe disposal of these bulbs can lead to significant exposure of human beings and wild life to mercury contaminated water and food. Issues with mercury contamination and customer preference for full spectrum light has been fuelling the replacement of these lights particularly in areas like self managed residential complexes where people can directly pay for the quality of light.

Fluorescent lamps

The fluorescent lamp first became common in the late 1930s. These lamps are a form of discharge lamp where a small current causes a gas in the tube to glow. The typical glow is strong in ultraviolet but weak in visible light. However, the glass envelope is coated in a mixture of phosphors that are excited by the ultraviolet light and emit visible light. Fluorescent lamps are much more efficient than incandescent lamps, but less efficient than High Pressure Sodium.

The major problems with standard fluorescent lamps for street lighting is that they are large, and produce a diffused non-directional light. They are also susceptible to low voltage failure, prone to breakage of glass parts and contain harmful mercury. Therefore the fixtures needed to be large, and could not be mounted more than 20–30 feet above the pavement if they were to produce an acceptable light level. Fluorescent lamps quickly fell out of favor for main street lighting, but remained very popular for parking lot and outside building illumination for roadside establishments.

Compact fluorescent lamp

Compact fluorescent lamps (CFL) have been used more frequently as time has improved the quality of these lamps. These lamps have been used on municipal walkways and street lighting though they are still rare at this time. Improvements in reliability still need to be made. Some issues with them are limited lumen output, high heat build up in the self contained ballast, low life/burnout due to frequent cycling (on/off) of the lamp, and the problem where most fluorescent sources become dimmer in cold weather (or fail to start at all). They also contain harmful mercury. CFL efficiency is high and CRI is excellent around 85. CFL produces a color temperature around 3000 K with its light being "soft white" around that color temperature. Higher color temperatures are available.

Induction lights

Induction based fixtures are relatively new to the market. Induction lamps use radio frequency or microwaves to create induced electrical fields, which in turn excite gases to produce light. Induction lights have a rapid start-up and work at peak efficiency with minimal warm-up time, much like LED technology. This technology has some advantages versus HPS technology in the areas of efficiency and life cycle, however, initial cost barriers and the rapidly evolving nature of LED technology have led to limited adoption of induction based roadway lighting systems. Another limitation of Induction Lighting is that it has limited directionality when compared to LEDs. The life of induction light is negatively affected by heat and they also contain lead.

LED lights

Light emitting diodes are rapidly developing in light output, color rendering, efficiency, and reliability.
Achieving good maintenance-free thermal management in an often hostile environment while keeping product competitive is the largest challenge, which only few manufacturers managed to achieve. This latest high quality LED technologies are already exceeding all other available technologies by all technical parameters. According to its numerous advantages, even higher initial cost quickly pays for itself due to vastly reduced cost of electricity and maintenance. But to fully benefit from outstanding advantages it is important to educate and recognize the difference between low quality and latest state of the art LED technologies, since low quality LED alternatives have quickly spread all over the world.

Difference between low and high quality LED street lights

LED technology has developed dramatically over the last few years. The production of LED lighting luminaire is an extremely difficult process that requires a combination of advanced production lines, top quality materials and high-precision manufacturing processes.

Not many companies in the world meet the qualitative standards in the production of LED lamps. Because LED technology is increasing, there are a lot of inexperienced producers of LED street lights with very poor quality on the market.

Poor quality LED street lights can be worse than other types of existing energy-saving lamps on the market, while high-quality LED street lights exceed other types of street lighting in all technical parameters.

There is currently less than 100 experienced manufacturers of LED street lights in the world, of which less than 10 are able to produce high-quality LED street lamp with the highest quality standards. Those manufacturers are optimally exploiting full benefits of LED technology.

General benefits of high quality LED street lights

Below listed benefits of LED street lighting are related only to latest, high quality LED street lights:

Less energy consumption

LED street lights use 40-80% less electricity and have at least 5 times the life expectancy than regular High Pressure Sodium (HPS) fixtures.  LED lamps are 7 times more energy efficient than incandescent and twice as efficient as fluorescent lamps.

Higher efficiency and low light pollution due to directional light

LED street lights with a lower lumen output can replace conventional lamps with a higher output. For example, a 30W LED street light can often replace an 80W High Pressure Sodium lamp. The reason for this is directionality. LED street lamps are very directional and the light output is much more even then by other street lamps. Also there is little or no hot spot under the LED lamp. The light emitted from the LED lamp is directed downwards, spread throughout the entire area it covers. This means that a lower amount of light is needed to properly illuminate the area. This also dramatically reduces light pollution, which affects the mood of human beings, navigation in birds and insects, mating behavior in animals and flowering in plants.

Long life – up to 100.000 hours

LED street lights last much longer than conventional lamps (3 to 8 times longer). This results in less expense in replacing the lights themselves but also the labor to replace the lamp is needed less often. This provides a great cost savings by itself.
Also the loss of brightness or lumen depreciation is slower over the life of an LED lamp than that of a sodium or other lamp. So not only does the LED have a longer life span than the conventional lamp, but it stays brighter longer than other lamps. The long life span reduces maintenance expenses and makes these bulbs particularly suitable for difficult to reach locations and for streetlights where maintenance costs can be significant.

Great operating characteristics

LED operate at lower temperatures, are not sensitive to low temperature and unaffected by on off cycling. This makes them safer, more efficient in cold environments (outdoor lights, refrigerator lights and cold room lights) and better for applications requiring frequent switching on and off lights. These bulbs are shocks and vibrations resistant making them the best choice for places like bridges.

Reducing carbon footprint

The carbon footprint of LED street lights is smaller than other lights due to lower energy usage. Moreover LEDs last 4 to 10 times longer than any other bulbs, further reducing the carbon footprint of manufacture over the life time.

Darksky friendly

Because of the directional light, light is carefully distributed exactly where it is meant to go and therefore there is no or little light which is wasted by illuminating the night sky. This is a considerable plus especially if the local community has a Darksky Initiative.

Natural light specter – Color Rendering Index

LED street lamps with color temperature 3.500-4.200 K are rendering more natural light than the yellow of sodium lamps or green of flourescent streetlights. Also no UV or IR radiation is emitted from the LED street lamps. Color rendering index (CRI) is high (80-90) and displays natural colors of illuminated objects.

Free of harmful substances and lower environmental impact when used up

LED luminaires contain no harmful substances, like mercury, lead or other hazardous chemical and gasses. Spent LED lamps can be thrown away without any special handling or disposal requirement,since they are recyclable and environmentally friendly. Other light often have hazardous materials such as lead and mercury which require special handling and waste management procedures which have both economic and environmental costs.

Easily controllable

The light is easily controllable with intelligent systems. The light can be turned on and off instantly and can be dimmed for added energy savings at dawn, dusk, and also during hours of low traffic. Switching on-off and dimming does not affect the life-time of the luminaire as in the case of CFL lights.