With the rapid development of the current world economy, energy-saving and emission reduction become the basic national policy of China and the common goal of people all over the world. With the continuous development of LED technology, LED cost-performance continues rising.As a new light source, LED lights are widely used due to their low energy consumption, high luminous efficiency, small size, and other advantages.

In this article, we mainly introduce the application of LED in street lighting and further discuss the problems faced in the development of LED street lights. 

1. Application Of Road Lighting

When we make a road lighting design, we first need to choose the appropriate design standards based on the road type and then determine the construction standards reasonably. The basic principle is to achieve maximum energy saving with the lowest engineering investment. Meanwhile, we should also pay attention to functionality, aesthetics, and eco-environmental protection.

2. Common Street Lighting Type

At present, there are three types of street lighting that are commonly used: 

Wind and solar hybrid street lights 

Utility AC Power Street lights 

Solar energy street lights 

Each of those three types has its advantages and application emphasis, summarized as follows. 

       2.1 Utility AC power street lighting 

Utility AC power street lighting refers to traditional street lighting and led street lighting, which is commonly used in urban areas. Because of the excellent lighting efficiency, flexible and diverse installation, and easy maintenance, it is applied to a variety of road lighting systems. The disadvantage is that it needs to construct cables and configure the power supply equipment, and the installation requests large workload.  

　　2.2 Solar street light lighting 

Solar street light is a green street light lighting type with high technology content by absorbing sunlight without access to the municipal grid electricity, but through photoelectric conversion of solar energy into electricity, and with the LED light source to power the street light. The most outstanding advantage of solar street lighting is energy saving, environmental protection, the need to layout cable pipeline and power supply equipment, easy installation and construction, and low workload. 

Solar street light is a green street light lighting type with high technology content by absorbing sunlight without access to the municipal grid electricity, but through photoelectric conversion of solar energy into electricity, and with an LED light source to power the street light. The most outstanding advantage of solar street lighting is energy saving, environmental protection, the need to layout cable pipeline and power supply equipment, easy installation and construction, and low workload. The solar street lights automatically turn on and off via a controller sensing the sunlight brightness changing, so no manual operation to switch the solar street lights. 

The disadvantage of solar street lights is that their application is not as wide as the AC-powered type. solar street lights are applicable to the lighting of secondary roads and area lighting, but not applicable to the main road lighting in the central area of the cities. There can be no shading around the solar-led street lights. 

 In the past years, the Chinese government has put a lot of funding into the project of lighting up new rural areas, so that the lighting problems of many rural roads have been solved, bringing benefits to remote rural areas while also opening up market space for solar lighting.

      2.3 Wind and Solar hybrid street lighting  

The Wind-Solar hybrid street lighting can generate power by solar energy and wind power during the daytime, and continue to generate power by wind at night, which combines wind power and solar power to enhance the reliability and stability of the lighting system. 

The disadvantage of wind and solar hybrid street lights is that the system structure is complicated and the operation and maintenance cost is relatively high.

3. Advantages Of LED Street Light

　　Case 1: A campus road has more than 130 street lights, mainly to ensure that the campus road lighting, students back to the dormitory after the evening class lighting, and public lighting of the campus. Since the new campus was built and put into use, the lighting hours of the street lights are 18:00 to 5:00 p.m., with a power of 250 W for each street light. As the street lights are installed at a height of 9 m, it increases the difficulty of maintenance, requiring the use of bulky lifting platforms and multiple pushing and pulling, which take much time and labor. And the HPS street lights fail frequently (bulbs, ballasts, capacitors, triggers, etc. burn out). Ballast burnout will generally cause a short circuit to ground switch tripping, resulting in the area of the road power failure affecting lighting, students in and out of the activities are not safe, and troubleshooting is more troublesome (to remove the line one by one to investigate). And LED street lights have a long life, are lightweight, are maintenance-free are in line with the requirements of the school street lights. After observation, calculation, and application, after research and discussion, I decided to use LED street lights.

 Firstly, The comprehensive comparison shows that it will save 9,623USD( 12,056USD-2,433USD=9,623USD ) to install LED street lights on the campus roads., Compared to the original street lights, electricity costs were reduced by 9,623USD, which means saving four times the cost of electricity.

  Secondly, the ordinary street lights need to be replaced every 2 years, take the replacement cost into account, it would save 10,912USD to use LED street lights,  

Third, due to the life of the HPS( high-pressure sodium) lamp in 8000h (work 4015h/year), if street lights work 11h per day, the high-pressure sodium lamp life is generally 2 years. After 2 years of operation, over 80% of the street lights need to be replaced by new ones. We have seen that most of the HPS lamps failed in the compose after 2 years. While the LED street lights with a lifetime of 50000h, work 11h per day, the lifespan is over 12 years.   LED street lights mainly have 6 advantages:

   3.1 Comparison of LED street lights and traditional HPS street lights  

As a solid-state cold light source, LED street lights can convert electrical energy into light energy, with less environmental pollution and low energy consumption, as well as high luminous efficacy and longer life span.

　　3.2 LED street lights have high luminous efficiency and without light loss due to reflection

Most of the light emitted by LED lights can reach the irradiated object without reflection, maximizing the light, which effectively improves the efficiency of the street lamps, at the same illumination, the actual power consumption of LED is lower. Take 150W LED street light, for example, its initial luminous flux is 27750lm, because LED is unidirectional luminous, high efficiency of lamps and lanterns, 10% loss of lens, 10% loss of lamps fixture, the overall luminous flux of lamps is 22930lm, the total power of lamps is 175W, so the luminous efficiency of the LED street light is 135lm/W.

The luminous efficiency of a sodium lamp is about 90lm/W ~ 140lm/W, but because it is 360 ° luminous, only 30% of light can be applied to light subjects. So a reflector needs to be used in the fixture to improve the utilization rate of light. In fact, a lot of light in the spectrum does not play a lighting role, such as ultraviolet, red, and yellow light. Because of defects in lamp design and cost constraints, sodium lamp luminaire efficiency generally varies between 40% and 45%. For example, the 250W sodium lamp with an initial luminous flux of 30000lm, but the luminous flux of the luminaire only13500lm. That is, the actual power of the 250W sodium lamp is only 300W, and the luminous efficiency of the luminaire is 45lm/W, which is a low light utilization rate.

      3.3 LED street lights are driven by constant current, not affected by grid fluctuations

LED (Light Emitting Diode) is a semiconductor solid light-emitting device, it does not have a burning filament and ionized gas, mostly driven by constant current, which is different from traditional light sources.

　　3.4 LED street lights have a long lifespan and low maintenance costs

The LED lamp has a long life, is resistant to shock and vibration, is not fragile, and requires fewer maintenance costs. Comparing the cost of High-pressure sodium lamps and LED street lamp work in 10 years. 

LED street light and high-pressure sodium lamp use cost comparison

Due to the long service life of LED lights, further cost savings can be achieved in maintenance. On the other side, LED street light prices are going down.

      3.5 LED street lights do not contain lead, mercury, and other toxic elements, no pollution to the environment

　　High-pressure sodium lamps and other gas-discharge light sources work on the principle of the high-temperature action of the electric arc to excite the liquid sodium mercury gas luminescence. During the production process of gas-discharge light sources, the toxic mercury would pollute the environment, even after the failure of the light source in the process of disposal of waste products will also produce mercury pollution. According to statistics, since the industrial revolution, the mercury content of the earth’s atmosphere has risen more than 400 times. Once the soil, groundwater, and the atmosphere is polluted, it would be a huge threat to humans and plants, and animals, while LED street lights do not have these problems.

　　3.6 LED street light product diversification

LED street lights are generally modular designs, there are a variety of combinations, each LEDmodule is an independent light source and can be arbitrarily combined into different power and brightness requirements of the product, and the partial failure does not affect the normal work of the entire lamp, convenient disassembly, and maintenance. In addition, some LED products are designed with tubes, and can directly replace the existing street lamp, without replacing the lamp housing, saving the cost of light fixtures.

4. Problems encountered in the development of LED street lights

       4.1 Unbalanced development of technology

LED products do not have a clear national standard, the manufacturers are producing according to their own standards, the product type can not be universal, and the quality also varies very far, causing great trouble to the maintenance, maintenance, and replacement can only be referring to the original manufacturer. While LED street lights are in the stage of promoting strongly, their core technology is still controlled by several large LED manufacturers, the other manufacturers can only do the work of the assembly.

　　4.2 Investment cost and maintenance cost

　　LED street light project cost is higher than the price of high-pressure sodium lamps more than 2 times, although more energy efficient but the cost disparity is still relatively large. For example, calculations can be derived: the use of 75W LED street lights and 250W high-pressure sodium lamps in the use for 2 years after the cost and electricity is basically the same. But in theory, the high luminous efficacy of LED street lights, and long life characteristics, if they can give full play to the savings in electricity and its late maintenance costs, can make up the cost difference. This shows that the cost of its later use will be much lower than that of high-pressure sodium lamps.

Conclusion

At present, under the condition of resource shortage, energy-saving and environmental protection become the consensus of all people in the world, LED lighting has the advantages of low power, and low power consumption, in line with the national environmental protection and energy-saving policy, less radiation pollution, good stability, which makes LED lights become the best choice for road lighting.

If you want to learn more about solar street lights and traditional street lights, just click the following links for more information What you need to know about Solar street lights, advantages, and disadvantages. Solar Street Lights vs Traditional Street Lights, Comparison Advantages And Disadvantages. 12 Types Of Street Light Bulbs, Which is the Best?