In the 21st century, LED street lights have developed rapidly and become a more common source of illumination for streets and highways. Many communities have switched to LED street lights for all of their lighting needs. Environmental conservation has elevated to a top priority in many nations this century. Energy-saving LED street lighting have become a top choice for many nations to cut carbon emissions. Particularly in 2023, LED technology has replaced the original light source in many lighting circumstances. Meanwhile, high-pressure sodium lamps, as the mainstream light source for the past few years, also have their unique advantages. Many streets and highways are still using high-pressure sodium lamps as their lighting source. Below, we will introduce LED street lights Vs HPS street lights, and compare them in multiple aspects.
LED Street Lights VS HPS Street Lights: Performance
|Items||High Pressure Sodium||LED Street Light|
(Saves 60% more electricity compared to HPS)
|Color Temperature||2000 – 2500K||2700 – 7000K|
|Color Rendering Index||20 – 25||65 – 95|
|Voltage||AC200- AC230V||AC180V – AC265V|
|Luminous Efficiency||Low||High (minimal light decay)|
|Lifespan||<5000 hours||60,000 hours – 100,000 hours|
|Protection Level||IP65||IP65 – IP68|
|Startup Time||5 – 10 minutes||Instantaneous without delay|
|Continuous Startup||Not allowed|
(needs to wait for a few minutes)
|Environmental Protection||Mercury, UV radiation||No mercury; no UV|
|Heat Emission||High||Low (only 30% of HPS lights)|
LED Street Lights VS HPS Street Lights: Light Emission
LED (Light Emitting Diode) consists of a PN junction, with a core composed of a P-type semiconductor and an N-type semiconductor. When current flows through the LED, electrons from P-region, N-region and holes between them, recombine within a few microns of the PN junction. This process releases energy in the form of photons, resulting in spontaneous emission of fluorescence. The energy states of the electrons and holes in different materials of LEDs are different. When the electrons and holes recombine, they will release different amounts of energy. The shorter the wavelength of the emitted light, the greater the amount of energy released. The wavelength of light emitted by LEDs of different materials varies, resulting in different colors of light.
High-pressure sodium (HPS) lamps are high-pressure sodium vapor discharge bulbs, with a discharge tube made of a semi-transparent polycrystalline alumina ceramic tube resistant to sodium corrosion, which emits a golden white light when operating. After an HPS lamp is started, an arc is generated between the two electrodes of the arc tube. The high temperature generated by the arc vaporizes the liquid sodium and liquid mercury inside the lamp, creating sodium vapor and mercury vapor. At this point, the arc tube is filled with sodium vapor, which has a certain conductivity. When electrons emitted from the cathode of the arc tube collide fly toward the anode, the atoms are excited and release energy. This process produces light.
LED Street Lights VS HPS Street Lights: Luminous Efficiency
The luminous efficiency of high-quality LED light sources is currently around 140-160Lm/w for mainstream lighting fixtures. The luminous efficiency of high-pressure sodium (HPS) light sources is around 100Lm/w, and the light output per watt is higher than LED lights at around 40-80Lm/w. However, the luminous efficiency of a 400W HPS light can reach 120Lm/w. Considering that traditional light fixtures emit light in 360 degrees, after the light source is installed in the street light housing, most of the upward light does not form effective light, except for a small part that reflects to the road surface to form effective light, and the luminous efficiency is further reduced.
LED Street Lights VS HPS Street Lights: Fog Penetration
Regarding the fog penetration of LED lights used for road lighting, there is a lot of misunderstanding. The majority of individuals believe that LED street lights do not have good light penetration because they have seen some material online or have some sensory perceptions of the road, but they have not conducted any scientific assessments or analyses. A scientific study of this circumstance will be presented in this essay.
We all know that the range of visible light is between 380nm and 780nm, and all light within this range can be perceived and recognized by the human eye. That is to say, all lights within this spectral range have value for utilization. The spectral range of LED lights is more comprehensive than that of HPS lights. Both have peaks at 580nm, but the blue light portion of LED lights accounts for only 6% of the total luminous flux, while HPS lights have almost none. The distribution of LED light in the green-yellow region is broader than that of HPS lights.
The penetration of fog is more related to the color temperature. The color temperature of HPS lights is between 2700-3000K, while LED street lights now have very good and mature lighting effects in this range. Most people think that the reason for the poor fog penetration of LED lights is mainly due to the use of a color temperature range of 5000-6000K in early LED street lights, which has now been perfectly solved.
LED Street Lights VS HPS Street Lights: Color Rendering
The color temperature (Tcp) of LED street lights is between 4500-5000K, with a cooler color temperature. The spectrum of the light emitted by LED street lights is relatively wide, and the color is close to white light, with a good color rendering index (CRI) of 70-80. The color temperature of high-pressure sodium (HPS) lights is around 2100K, with a warmer color temperature. The spectrum of the light emitted by HPS lights is relatively narrow, with a yellowish color. The color rendering index is poorer, only 23-25. As fast lanes and main roads for vehicles, the yellowish HPS lights are slightly better for seeing the road conditions at a distance of 90-160 meters ahead, especially under foggy or dusty air conditions. For sidewalks, commercial pedestrian streets, residential areas, and other roads, LED lights have better color rendering, making it easier to distinguish people’s conditions, and have an advantage.
LED Street Lights VS HPS Street Lights: Energy Efficiency
The best way to compare the energy efficiency of LED lights and high-pressure sodium (HPS) lights is to do so at the same level of brightness. When the brightness and lighting quality of the two lights are comparable, we can compare their installed lighting power. There is a significant difference in the light efficiency of HPS lights with different power levels. The light efficiency of LED lights is not related to their power, but to the type of LED chip. In 2023, high-quality LED lights on the market have an energy efficiency of 90-130lm/W. Let’s compare the energy efficiency of the two types of lights in high-power and low-power situations.
(1) The light efficiency of high-power (250-400W) HPS lamps can reach 130-140lm/W, but in practical use, there are losses from rectifiers, light utilization, and lamp loss, so the overall efficiency is only about 55%. Therefore, the actual light efficiency of HPS lamps is 70-75lm/W. The overall efficiency of LED lights is very high, and their actual light efficiency can reach 85-100lm/W. The energy consumption of high-power LED lights is slightly better than that of HPS lamps.
(2) The light efficiency of low-power HPS lamps is already relatively low, and with losses from the lamp fixture, the light efficiency is only 45-55lm/W. However, the light efficiency of LED lights does not change with changes in power, and remains at 85-100lm/W. The light efficiency of LED lights is significantly better than that of HPS lamps.
High-power LED lights are about 25% more energy-efficient than high-power HPS lights, and low-power LED lights are about 45% more energy-efficient than HPS lights. Compared to HPS lights, LED lights are more energy-efficient and environmentally friendly.
LED Street Lights VS HPS Street Lights: Price
The price of a set of high-pressure sodium lights is around 1200-1500RMB. The price of LED street lights is around 2000-5000RMB, with different power LED street lights having different prices. If we only compare the prices, LED lights are about 2-3 times more expensive than high-pressure sodium lights. However, LED lights are more energy-efficient. High-power LED street lights save about 25% more electricity than high-power HPS lights, and low-power LED street lights save about 45% more electricity. Replacing HPS lights with LED lights can save about 260-500 kWh of electricity per year. In this way, it can recover the additional cost of purchasing LED lights. The cost can be recovered in a normal 3-year period, showing that LED lights have good economic benefits.
Looking to the future, with the gradual improvement of overall lamp efficiency, LED street lights will have better energy-saving performance. In addition, with the good controllability of LED lights and the addition of smart systems, the amount of electricity saved will increase significantly, resulting in even better economic performance and maintenance cost savings. This is one of the important reasons why LED street lights are replacing traditional light sources.
LED Street Lights VS HPS Street Lights: Service Life
When comparing their service lives, we should consider the entire life of the lamp. High-pressure sodium (HPS) lamps consist of the light source, electrical accessories (mostly ballasts and triggers), and lamp fixtures. The average service life of HPS lamps used for streetlights is 1 to 2 years, and the lamp fixtures are the same.
Different from the myth that LED lights are fragile, they have a long service life due to continuous development. The best domestic companies can guarantee a lamp life of around 50,000 hours. Based on a daily use of 12 hours, they can last for more than 10 years. One of the reasons for its long service life is the special thermal design of LED lights. Therefore, overall, the service life of LED streetlights is much longer than that of traditional HPS streetlights, and maintenance costs have greatly decreased. It is also a factor that most buyers will consider when choosing LED street lights.
LED Street Lights VS HPS Street Lights: Maintenance
When street lighting management departments purchase streetlights, the maintenance charge is a key consideration. So streetlights with good maintenance performance will have an advantage in government procurement. HPS lamps are streetlights with good maintenance performance. Their lamp fixtures and ballasts have a long service life and do not need to be replaced. Only the lamp fixtures need to be cleaned. The light source of HPS lamps needs to be replaced every 2-4 years, which is also very convenient.
As of today in 2023, LED streetlights have better maintenance performance. LED streetlights have a long service life and only need to clean the lamp fixtures. You may need to replace some lamps that have been damaged by unexpected factors, but the maintenance is not frequent. For areas with harsh environments, it is only necessary to regularly clean the surface of the lamp fixture to ensure the normal operation of the lamp fixture. Moreover, modularized LED lamp fixtures have already appeared, which makes maintenance and replacement simple and cost-effective. LED streetlights already have standards to follow, which ensures that they can be tendered, ordered, used, and maintained.
In summary, we believe that LED streetlights are already trending towards maturity. With the development of the LED industry, there will inevitably be greater development and broad prospects. Although there are still some small problems in the current application status, companies engaged in LED streetlight research, development, and production have made great efforts and will gradually solve these problems, promoting the industry’s progress.