LED Street Light VS HPS Street Lights

Comparison of the luminous principle of LED lamps and high-pressure sodium lamps

LED light Emitting Principle

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 consists of three parts, one part is a P-type semiconductor, in which holes dominate, and the other end is an N-type semiconductor.
When the current acts on the chip through the wire, the electrons and holes will be pushed into the quantum well. In the quantum well, the electrons recombine with the holes, and then they will emit energy in the form of photons. This is the principle of LED light emission. The wavelength of light is the color of light, which is determined by the material forming the P-N junction.

Luminescence Principle of 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 temperature of the arc, the sodium amalgam in the tube is heated and evaporated into mercury vapor and sodium vapor. The electrons emitted by the cathode collide 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.

The Uniqueness of LED Street Lights

The high-power LED street lamp is a new type of lighting method that realizes the 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 the LED street lamp is low voltage DC, it can be The combination of solar energy makes solar LED street lights a possibility for road lighting in the future.

1. The characteristics of the LED street light itself-the unidirectional light, no light diffusion, to ensure the light efficiency.
2. The LED street light has an automatic control energy-saving device, which can achieve the greatest possible reduction in power and energy saving under the condition of meeting lighting requirements at different times.
3. Each unit LED chip has only a small volume, so it can be prepared into various shapes of devices and is suitable for variable environments.
4. Long lifespan: It can be used for more than 50,000 hours and has high luminous efficiency. At present, the luminous efficiency of LED lights from Tachyon reaches 150~200lm/W or even higher.
5. Easy installation: No need to add buried cables, no rectifiers, etc., just install the lamp head of the street lamp on the lamp pole or embed the light source into the existing lamp shell.
6. Reliable quality: All circuit power supplies use high-quality components, and each LED has a separate overcurrent protection, so there is no need to worry about damage.

The Advantages of LED Street lamps Compared to Traditional HPS Lamps

Energy saving

The efficiency of the LED light source has reached 150-200lm/W, and there is still a lot of room for development, with a theoretical value of 250lm/W. The luminous efficiency of high-pressure sodium lamps increases with the increase in power. Therefore, the overall luminous efficiency of LED street lamps is stronger than that of high-pressure sodium lamps.
Using high-power LED light sources with high-efficiency power supplies, the actual lighting effect has been tested compared to the current high-pressure sodium lamps used on the road. Energy saving is more than 60%, and there is still a lot of room for technological progress. With the rapid improvement of LED efficiency, LED street lamps have shown great potential in energy saving.

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. Due to the high luminous efficiency of high-power lamps (250~400W) of high-pressure sodium lamps, which can reach 130~140 lm/W, the luminous efficiency of low-power lamps (100~150W) is about 80~100 lm/W. Power LED street lights mostly use 1W LED tubes, which have similar luminous efficiency, so it is advisable to analyze high-power street lamps and low-power street lamps separately.

(1) High-power (≥250W) street lamps: high-pressure sodium lamps have high lighting efficiency, considering three factors such as 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 lm/W; The effective luminous efficiency of LED street lights is currently about 100 lm/W, and the best domestic companies have reached 180~200 lm/W. Therefore, for high-power street lamps, LEDs are currently more energy efficient than sodium lamps.

(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 is still calculated at 100~120 lm/W, the LED can achieve energy saving than sodium lamps 70%~80%, up to 90%. From the above analysis, it can be seen that when the low power (≤150W) of the branch is used, the LED street lamp can save energy by 10%~30% than the sodium lamp, and the high-power LED street lamp can save 50%, 60% energy than the high-pressure sodium lamp, so the future LED It will be the general trend that lights completely replace HPS.

Good color rendering

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. The color temperature currently used by LED street lights is mostly greater than 5300K, which is a cool color temperature. The color rendering of better LED street lights is much higher than that of high-pressure sodium lamps, and its Ra can reach 70~90, and the color rendering is good. From the perspective of visual psychology, to achieve the same brightness, the illuminance of LED street lights can be reduced by more than 20% than high-pressure sodium lamps on average. And the road looks brighter, feels more comfortable, and the driver feels safer.
As a fast lane and main road for motor vehicles, the sodium lamp with a yellowish light is slightly better than white light for seeing the road conditions about 90~160m ahead, especially for foggy and dusty air conditions. It has advantages. For roads such as sidewalks, commercial pedestrian streets, and residential quarters, the color rendering of LEDs is better than that of sodium lamps, and the status of people can be distinguished more clearly, which has advantages.

Long lifespan

LED street lights have low light decay, less than 3% in one year, and still meet the road illumination requirements after 10 years of use, while high-pressure sodium lamps have large decay, which has dropped by more than 30% in about a year. , LED street lamps can be designed with lower power than high-pressure sodium lamps and have a longer life. The comparison service life should be based on the whole lamp life. High-pressure sodium lamps include light sources, electrical accessories (mainly ballasts, triggers) and lamps.
Sodium lamps are used for street lamps with an average life span of 3 to 5 years. Energy-saving inductive ballasts will not be less than 20 years, and the same is true for lamps. The existing LED lamps can generally achieve 50,000 to 60,000 hours. The main reason is that the life of the LED chip is very long, but it has a great relationship with many factors such as temperature and heat dissipation after packaging. In addition, there is also the life of the electronic components of the drive circuit device.

Green and environmental protection

LED does not contain harmful metals such as mercury and other heavy metals, and will not produce pollutants, unlike high-pressure sodium lamps or metal halide lamps that cause harm to the environment when they are scrapped.

Low maintenance cost

According to the current technical level and test results, the high-power LED light source can be used normally for 10 years without replacement, while the traditional high-pressure sodium lamp needs to be replaced once a year and a half on average. The use of LED light sources can greatly reduce maintenance costs .

Optional color temperature

LED can meet the needs of color temperature in different occasions. Indoor and outdoor color temperature requirements are different. Home lighting is not the same as commercial lighting. In addition, some stores need alternative white LED lights to make their products more fashionable and sophisticated. Satisfy the appetite of shoppers from the color. The color temperature of the high-pressure sodium lamp is too low, making people depressed and hypnotic. The yellow light in summer may give people a hot feeling.

High safety factor

LED street lights are low-voltage products. Of course, this is for solar LED street lights. 12V is enough, and the voltage of city power LED street lights is still 220V.

Fog penetration

There is a big misunderstanding about the penetration of heavy fog in LED street lamps in road lighting. Most people have always believed that the penetrability of LED street lights is lower than that of traditional sodium lamps, which is a wrong understanding. . The distribution of LED red light area is wider than that of high pressure sodium lamp.