Does LED street lamps better than high-pressure sodium lamps?

At present, China is creating a resource-saving and environment-friendly society, and the concept of "green lighting" is gradually gaining popularity. With the continuous advancement of science and technology and the rapid development of semiconductor material application technology, low-power LED light sources have been widely used in landscape lighting, and high-power LED street lights have attracted more and more attention from all aspects.

These two technologies are completely different methods of producing light. Sodium vapor bulbs contain metals that evaporate into an inert gas within a glass envelope, while LEDs are a solid-state technology. Both technologies are extremely efficient. The difference is that sodium vapor lamps were the most efficient technology in the 1970s, while LEDs are the most efficient technology today. Although sodium vapor lighting beats nearly every other technology in terms of energy efficiency (which is why it was chosen to light up many city streets), it loses out to LEDs. Both LEDs and sodium vapor lamps emit electromagnetic radiation within a small portion of the visible spectrum, but LEDs waste far less energy as waste heat, and they also offer users an incredible variety of high color rendering index options (thus eliminating the monochromatic black appearance of objects illuminated by LPS and HPS bulbs).

The biggest difference between LED lamps and high-pressure sodium lamps is the color temperature and color rendering index. LED lights have a wider range of color temperatures as well as a higher color rendering index. LED area lights have easier intrinsic than high-pressure sodium lamps.

1. Comparison of luminescence principle

1.1 The luminous principle of LED lights

LED (Light Emitting Diode), a light-emitting diode, is made of III-IV group compounds. It is a solid-state semiconductor device that can directly convert electricity into light. The heart of the LED is a semiconductor chip. The semiconductor chip is composed of three parts. One part is a P-type semiconductor, in which holes dominate, and the other end is an N-type semiconductor. The electrons and holes will be pushed into the quantum wells when the current acts on the chip through the wire. In the quantum wells, the electrons recombine with the holes and then emit energy in the form of photons. This is the principle of LED light emission. The wavelength of light is also the color of light, which is determined by the material forming the P-N junction.

1.2 The luminous principle of the HPS lamp

The high-pressure sodium lamp uses electricity to generate an arc between the electrodes at both ends of the arc tube. Due to the high arc temperature, the sodium amalgam in the tube is heated and evaporated into mercury vapor and sodium vapor. The electrons emitted by the cathode impact and discharge during the movement to the anode. The atoms of the substance gain energy to produce ionization or excitation and then return from the excited state to the ground state or change from the ionized state to the excited state and then return to the ground state in an infinite loop. At this time, the excess energy is released in the form of light radiation. Then there is light. High-power street lighting is a new type of lighting method that realizes lighting needs by illuminating the LED group by DC low voltage. It has the characteristics of high brightness and good color rendering. In addition, because the input of street lighting is low voltage DC, it can be. The combination of solar energy makes solar outdoor LED street lights a possibility for road lighting in the future.

2. About energy efficiency analysis and comparison

The lighting installation power of the two should be compared on the premise of reaching the same illuminance (brightness) level and similar lighting quality standards. Because the high-power tube (250~400W) of the high-pressure sodium lamp has high luminous efficiency, it can reach 130~1401m/W, while the luminous efficiency of the low-power tube (100~150W) is about 80~100 lm/W, while the current high-power LED 1W LED tubes are mostly used in led street lamp, and their luminous efficiency is much higher. Therefore, it is advisable to analyze high-power LED road lights and low-power street lamps separately.

2.1 High-power (≥250W) street lamps

High-pressure sodium lamps have high lighting efficiency, considering three factors: ballast loss, lamp efficiency, and light channel utilization. If the overall efficiency is calculated as 0.55, the effective light efficiency of the sodium lamp is about 70~75 1m/W; and the effective luminous efficiency of outdoor led light street, the best domestic enterprise has reached 1701m/W. Therefore, for high-power street lamps, LEDs are much more energy-efficient than sodium lamps.

2.2 Low-power (≤150W) street lamps

The effective luminous efficiency of sodium lamps (included in the overall efficiency of 0.55) is about 45~551m/W, while the led road light is still calculated at 170 lm /W, the LED can achieve 75% energy saving than sodium lamps. Up to 80%.

3. Analysis of the light color of the light source on the road lighting effect

The correlated color temperature (Tcp) of the high-pressure sodium lamp is about 2100K, which is a warm color temperature, and its color rendering index (Ra) is only 23~25, and the color rendering is low; and the color temperature currently used by outdoor led street light is mostly 4500K-5300K, which is a cool color temperature. A better product, its Ra can reach 70~80, and its color rendering is good. As a fast lane and main road for motor vehicles, the sodium lamp with a yellowish light is slightly better than the white light for seeing the road conditions about 90~160m ahead, especially for foggy and dusty air conditions. It has advantages. For sidewalks, commercial pedestrian streets, residential quarters, and other roads, the color rendering of LEDs is better than sodium lamps, distinguishing people's conditions more clearly, and has advantages.

4. Economic analysis and comparison

High-pressure sodium lamps are about USD150-200 per set; at present, the street light cost varies greatly according to the power size, which is about USD 80-300. As far as the status quo is concerned, LED street light fixtures are slightly more expensive. However, LED can save energy by 75%. Replacing the original 150W high-pressure sodium lamp with an led streetlight saves about 500KWh of electricity per lamp every year, which can recover the extra cost of lamp purchase. Normally, the cost can be recovered in 1-2 years, and the LED lamp has shown good economic efficiency. Looking to the future, with the gradual improvement of the light efficiency of LED road light sources, the overall lighting efficiency of the lamps will increase accordingly, and the energy-saving performance will be better. Street lamps will be popularized with low power. The price of LED streetlights will also be reduced, gradually eliminating traditional light sources.

5. Service life analysis

The comparison service life should be based on the whole lamp life. High-pressure sodium lamps include light sources, electrical accessories (mainly ballasts and triggers), and lamps. Sodium lamps are used for street lamps with an average life span of 1 to 3 years. Energy-saving inductive ballasts will not be less than 20 years, and the same is true for lamps. The service life of the LED streetlight has been used. Existing domestic companies have done their best to guarantee the life of the lamps to be about 100,000h. The road lighting can be used for more than 20 years if it is used for 12 hours per day. So, overall, the service life of an LED streetlight is much longer than that of traditional sodium street lighting.

6. Maintain performance comparison

Users represented by urban street light management departments are more concerned about the maintenance performance of LED road lights. According to the analysis, the maintenance performance of the sodium lamp is good. The lamp only needs to be scrubbed and does not need to be replaced. The ballast is rarely replaced. The light source is replaced every 1 to 3 years, which is very inconvenient. In addition to the occasional damage to the power supply during the service life of the road lamp, almost no maintenance is required. For areas with harsh environments, only the surface of the luminaire needs to be cleaned regularly to ensure the normal operation of the luminaire, and there are now mature modular LED road lights. Appears maintenance and replacement are simple, and the cost is very low. Outdoor LED street lights already have standards to follow, and there are guarantees for bidding, ordering, use, and maintenance. In summary, we believe that outdoor LED street lights have become mature, and with the development of the LED industry, there will be greater development and broad prospects.

7. Luminous efficiency

The luminous efficiency of the LED light source, the LED street lighting effect produced by Hylele, can reach up to about 170 Lm/w. The luminous efficiency of the high-pressure sodium lamp light source is about 100Lm/w, and the luminous flux emitted per w is 40-80Lm/w lower than that of the LED. The luminous efficiency of a 400-watt high-pressure sodium lamp is as high as 120Lm/w. 

8. Fog permeability

In road lighting, there is a big misunderstanding about the penetration of street lighting in heavy fog. Most people have always believed that the penetrability of LED street lamps is lower than that of traditional sodium lamps, which is a misconception. Most people see some information from the Internet or see some sensory feelings on the road without scientific evaluation and analysis, so they think that the light penetration of street lighting is poor. In this article, we will make a scientific analysis of this situation. We all know that the range of visible light is between 380nm and 780nm, and light in this range can be accepted and recognized by the human eye. All lamps and lanterns have use-value only in the range of this waveband, and the human eye cannot recognize it outside this range. The analysis of penetrability in this article is only carried out within this scope. It can be seen from the spectrogram that the spectrum of the LED is much more comprehensive than that of the sodium lamp. The peaks of both are at 580nm. The blue part of the LED only accounts for about 6% of the total luminous flux, while the sodium lamp has almost none. The distribution of the red-light zone of the LED is wider than that of the high-pressure sodium lamp.

9. Dimming function

Outdoor LED street lights have a perfect dimming function. The light output of LED lamps is directly proportional to the working current, so the light can be dimmed by reducing the current. In addition, since the frequent switching of the LED lamp does not cause much damage to it, the LED lamp can also be dimmed by pulse width adjustment. By adjusting the duty cycle of the voltage and the operating frequency, the luminous intensity of the LED streetlight can be effectively adjusted.

10. Performance comparison

led vs sodium street lights

 

‌In conclusion，LED street lights have significant advantages over high-pressure sodium lamps, mainly in terms of energy efficiency, lifespan, maintenance cost, environmental protection, and intelligent control.

Lifespan and maintenance cost

Lifespan‌: LED street lights have a longer lifespan and less light decay, while high-pressure sodium lamps have greater light decay, which can reach more than 30% in about a year.
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Maintenance cost‌: LED street lights reduce the frequency of bulb replacement and maintenance costs, and the materials of LED lamps can be recycled, further reducing maintenance costs.

Environmental protection

Environmental protection‌: LED street lights do not contain harmful metals such as mercury, waste can be recycled, the working temperature is low, there is no ultraviolet and infrared radiation, the glare is small, and no light pollution is generated.

‌Energy saving and emission reduction‌: LED street lights have lower power. For example, the effect of 250W high-pressure sodium lamps and 120W LED lamps is similar, but LED lamps have lower power consumption. If it is calculated as a city with 20,000 street lights, carbon emissions can be reduced by 5,200 tons per year, saving about 14 million yuan in electricity bills.

Intelligent control

LED street lights have automatic control energy-saving devices, which can realize computer dimming, time period control, light control, temperature control, remote control, and automatic light inspection, and have a more humanized design.