Advantages and Applications of LED Street Lights

Advantages and Applications of LED Street Lights

Street lighting, with the exception of private property, is publicly owned and controlled by the government. Since LED has high efficiency, environmental protection, energy saving and long life features, it should be the first LED light source to be applied in street and tunnel lighting.

Lamps used in road lighting are called street lamps. Road lighting fixtures that use LEDs as a light source are called LED street lights. The essence of LED street lights is the LED light source. The LED street light source consists of a large number of high power white LEDs connected by a hybrid connection. In addition to LED modules, LED street lights also contain drivers, optical components and heat dissipation devices.

Development Status of Road Lighting

Road lighting emerges when people need to travel at night. Modern road lighting began with the advent of incandescent lamps. Road lighting is being developed with the development of the era, the advancement of science and technology, and the continuous improvement of people's living standards. Starting from the situation where people only need to illuminate the pavement to detect the road, they need LED street lighting to help people identify the warnings and signs on the road, and to assist motorized and non-motorized vehicle drivers.

The main purpose of road lighting is to provide drivers and pedestrians with good visibility conditions and direct them to move, to improve traffic efficiency, reduce nighttime traffic accidents and crime, and also to help pedestrians see the environment and determine directions. With the development of the social economy and the continuous improvement of people's living standards, people go to more and more outdoor entertainment, shopping, sightseeing and other activities at night. Good road lighting also plays a role in living comfort, improving the economy and strengthening the city's image.

From the lighting point of view, roads can be divided into four categories: driveways only, public streets, commercial streets, and sidewalks. In general, road lighting refers to special road lighting for cars. Among the many purposes of road lighting, providing safe and comfortable viewing conditions for motor vehicle drivers is the first priority.

The source of road lighting was first high-pressure mercury lamps, then high-pressure sodium (HPS) lamps and metal halide lamps, high-efficiency energy-saving lamps, induction lamps and LED lamps appeared one after another. Among the more mature street lighting sources, HPS lamps have the highest luminous efficiency, usually reaching 100~120lm/W. In the current Chinese road lighting market (about 15 million lamps), high-pressure sodium lamps occupy more than 60% of the market. . In some communities and rural roads, the lighting sources are mainly electronic energy-saving lamps (CFLs), accounting for about 20% of the road lighting market. Traditional incandescent lamps and high-pressure mercury lamps are being phased out.

Description of LED Light Source and LED Street Light

Light-emitting diode, abbreviated as LED, is the abbreviation for light-emitting diode in English. Its light-emitting principle is to use solid semiconductor chips as light-emitting materials. When a forward voltage is applied to both ends, minority carriers and majority carriers are injected into the PN junction of the semiconductor material. When the currents recombine, photons are emitted to produce light, which converts electrical energy directly into light energy.

As a solid light source, LED was originally used as an indicator light and instrument panel, but with the development of technology, it can already be used as a light source. It can not only convert electrical energy directly into light energy with high efficiency, but also has a theory. It has a service life of up to 100,000 hours and many advantages, such as environmental protection and mercury-free, rich colors, continuous switching and flashing, 0% ~ 100% dimming function, and the output light does not flicker, which makes it highly efficient. and energy saving The development trend of a new generation of environmentally friendly light sources.

LED street lamp is a product integrating LED light source technology, LED light controller technology, LED module connector technology and lamp design technology. The application of high-power LED lamps to road lighting has been the focus of the lighting industry in recent years.

The People's Ministry of Science and Technology rapid implementation of LED lamps in street lamp projects in large cities, in order to promote energy saving and emission reduction, and effectively guide the healthy and rapid development of semiconductor lighting applications. Local governments have used LED street lights in their lighting projects as an important task for energy saving and emission reduction.

Advantages of LED Street Lights

Compared with traditional street lamps represented by high-pressure sodium lamps, LED street lamps have many distinct and potential advantages.

High luminous efficiency, low energy consumption

Currently, the luminous efficiency of high-power white LEDs has exceeded 100lm/W and the laboratory level of high-power white LEDs of companies such as Philips and Osram, which SOLI Lighting uses for its products, reached 160lm/W as early as 2009. According to the US Department of Energy's (DOE) forecast, by 2022 the luminous efficiency of high-power LED commercial products can reach 165lm/W and the luminous efficiency of laboratory samples can reach 230lm/W. After 2022, the luminous efficiency of LED will basically no longer be greatly improved and will enter a period of lag.

In terms of road lighting, high pressure sodium lamps dominate due to their luminous efficiency of 120lm/W. However, with the continuous improvement of LED light efficiency, the monopoly position of high-pressure sodium street lights is in jeopardy. At present, LED street lights below 150W used in secondary roads have shown obvious energy-saving advantages.

Conventional street light sources often illuminate the entire area, but only traffic and pedestrian paths need to be illuminated with streetlights. For this reason, in the design of street lamps, curved reflectors are needed to reflect the lights to the road as evenly and intensely as possible, to collect the light and make it shine in the desired direction. In the light propagation process, the light output efficiency of the street lamp is only 65% to 70%, due to the blocking of the light source and the absorption of the reflective surface. In contrast, LED street lights, due to their good versatility, the efficiency of the lamp can reach about 80% when using secondary optical lenses. If the optical design is done three times, the light output efficiency of the lamp can reach 85~90%.

Facts have proven that replacing the 250W high-pressure sodium street lamp used on the secondary road with a scientific and reasonable 100W LED street lamp not only provides the average illumination required by the road lighting standard, but also greatly improves the homogeneity. The average illuminance of street lamps with high pressure sodium lamps may be higher in local areas, but the homogeneity is poor. It can be seen that LED street lights have significant energy saving space. High-intensity discharge (HID) streetlights are generally dimmable only within a small range, while LED streetlights can provide dimming control from 0% to 100% and flexibly adjust the light output according to ambient light and traffic conditions. Reduce unnecessary energy consumption while meeting lighting requirements. In road lighting, which accounts for about 15% to 20% of the total lighting power consumption, large-scale application of LED street lights is of great importance in terms of energy saving and carbon reduction.

Long service life

The lifetime of street lights directly affects the maintenance cost of all road lighting. At present, the life of high-pressure sodium lamps is generally about 20,000 hours, the life of high-pressure sodium lamps for road lighting is only about 5,000 hours, and the lifespan of high-power LEDs generally reaches 50,000 to 70,000 hours.
The average life of high-pressure sodium lamps and LEDs is defined differently. The average life of a high-pressure sodium lamp is defined as the "time to burn a group of light source samples tested to 50% of the damage number", while the average lifespan of an LED means that "a series of LEDs will experience light decay".

If the LED is measured according to the life definition of a high-pressure sodium lamp, an LED with a lifespan of 50,000 hours can reach 100,000 hours; If a high-pressure sodium lamp is measured by the definition of an LED's lifespan, a high-pressure sodium lamp with a lifespan of 20,000 hours has a lifespan of approximately 10,000 hours.

Of course, the lifetime of LEDs is not the lifetime of LED street lights. The life of LED street lights is determined by the life of the LED light source and the life of the driver circuit. The lifetime of the LED and driver circuit depends on the heat dissipation capacity of the lamp, the circuit topology and the choice of electronic components. Based on the current technical level, the lifespan of LED street lights can far exceed that of high-pressure sodium lamps.

Good color rendering

Although the high-pressure sodium lamp has the highest luminous efficiency among conventional light sources, its color rendering is the worst, with a color rendering index Ra of only about 20. This kind of poor color rendering can help people perceive road conditions, but it cannot. help pedestrians distinguish clearly. The color rendering index of LEDs can reach around 80, which is basically close to natural light, presents colors more realistically, and can better reflect the color of the object itself. The high color rendering of LEDs will undoubtedly help drivers and pedestrians identify targets and provide better traffic conditions under the same road brightness.

Quick start

The incandescent lamp will light up at some point, but the actual start-up time is about 0.1 to 0.2 seconds. Gas-discharge lamps, such as high-pressure sodium lamps and metal halide lamps, take tens of seconds or even ten minutes to begin their steady light output. Once turned off, it takes 3 to 6 minutes to cool before starting. The LED start time is only tens of nanoseconds (ns), there is no waiting time for reboot, and the LED lamp can work normally in a continuous on/off state.

Simplify optical design

The LED is small in size and can emit light in the half-plane direction. It can be considered as a point light source in the design of the lamp. It is very suitable for the use of lenses or reflectors for optical design to achieve a more ideal light distribution and higher lamp efficiency.

Strong plasticity and solid construction

The shape of the LED street light has strong plasticity, and the decoration and local humanistic features can be reflected by the shape design, adding the added value of beauty and urban image.

The LED is a solid state light source and does not contain sensitive parts such as glass and filaments. With reasonable design, LED lamps can be made very solid in structure.

Low carbon and environmental protection

Gas discharge lamps such as high-pressure sodium lamps, especially suitable for the use of solar photovoltaic technology, contain mercury and other harmful substances that will cause serious long-term pollution of the environment and water resources after the light source is abandoned. The LED chip and package can meet the requirements of the EU RoHS Directive and are free of harmful substances such as mercury and lead. After the LED is thrown away, it can be recycled and does not pollute the environment.

The characteristics of the LED driver are particularly suitable for the application of solar photovoltaic technology and wind-solar complementary technology to road lighting, to achieve real energy saving and environmentally friendly lighting.

Potential total cost advantage

At present, the unit price of LED street lights is 4 times higher than the unit price of high-pressure sodium lamps. The 250W LED street light has the same effect as the 400W high pressure sodium street light, but the price of the first is 6000~8000 yuan, and the second is only 1500 yuan. However, as long as the high luminous efficiency and long life characteristics of LED street lights can be fully exploited, the savings in electricity and maintenance costs and the initial cost difference can be recovered. With the gradual maturation of LED street lighting technology and the continued reduction of initial cost, it will not be long before its potential advantages in overall cost become apparent.

The Technical Challenges That LED Street Lights Need To Solve

If LED street lights are to be implemented on a large scale and become the main light source of road lighting, there are still some challenges to be resolved. In summary, there are three main challenges: optical design, heat dissipation issues, and drive power supply design.

Optical design

Streamlining optical design is actually a big advantage of LED street lights, but it's also a big challenge. The light distribution of LED street lights includes primary light distribution (using encapsulated lens), secondary light distribution and tertiary light distribution. When the requirements for road surface brightness, illuminance and uniformity can be met with secondary light distribution, there is no need for a third optical design. In order to meet the requirements of road lighting, the light distribution of LED street lights must be designed repeatedly to achieve what is needed.

At present, people have developed many LED street lamp light distribution schemes, such as LED primary light distribution (i.e. lens package) plus secondary light distribution of lamps, secondary light distribution of LEDs (using secondary lenses) plus tertiary light distribution of lamps and reflectors. But no matter what kind of light distribution scheme, it cannot be scientific and reasonable. To varying degrees, there are issues such as low overall optical efficiency, large glare, road brightness, and poor illumination uniformity. How to choose the light distribution method, how to choose the lens, how to improve the structure of the street lamp to meet the light distribution and heat distribution requirements are important points that are only resolved by competent companies such as SOLI Lighting.

Heat dissipation issues

The heat dissipation capacity of LED street lights directly affects the actual luminous efficiency and lifetime of the LED.

LED is an electroluminescent device. In the working process, only 15% to 25% of the electrical energy is converted into light energy, and the rest of the electrical energy is almost converted into heat energy, which increases the temperature of the LED and causes a sharp decrease in the luminous efficiency. If the LED junction temperature exceeds the maximum allowable temperature (usually 125°C), the LED will be damaged due to overheating. Therefore, the most important task in the design of LED lamps is the design of heat dissipation.

The heat dissipation system of LED lamps includes the heat dissipation of the LED module and the heat dissipation of the heat sink on the lamp structure (such as the body). The latter is the current common method of heat dissipation. Due to the harsh working environment of LED street lights, dust and flying insects are easy to accumulate, The surface of the radiator is easy to wear and oxidize, which will affect the heat dissipation of the LED and electrical appliances in the lamp, resulting in a shortened service life of the LED street light.

To solve the heat dissipation problem of LED street lights, micro fans can be configured on the lamps for active forced heat dissipation, but the service life of heat dissipation fans in the harsh outdoor environment is difficult to meet the requirements.

The weight of LED street lights is mainly determined by the weight of the cooler. As the power of LED street lights increases, the size and weight of the radiator must increase accordingly. In order to reduce the weight of the high-power LED street lamp heat sink, it is necessary to optimize the design of heat dissipation methods, heat dissipation structures and materials.

Competent and experienced lighting companies such as SOLI overcome all these problems and bring the area that needs lighting to light in the most optimum way. Company selection is important in lighting. Contact us and we will provide the lighting you need with SOLI assurance.