In the night scene of modern cities, street lights not only assume the basic function of illuminating roads and ensuring traffic safety, but also are an important reflection of the city’s image and quality of life. High-pressure sodium lamp (HPS) and light-emitting diode (LED) street lamps as the current urban street lighting of the two mainstream technologies, the differences between them have a profound impact on the planning, construction and operation and maintenance of urban lighting systems. An in-depth analysis of the differences between the two in terms of efficiency and brightness, cost, color temperature, service life and warm-up time is of great significance for optimizing urban lighting, realizing energy saving and emission reduction, and reducing operating costs.
solar street light
At one time, HPS street lights dominated the street light market with their excellent light efficiency. For a long time, HPS street lights were able to achieve a luminous efficacy of up to 90 lm/W. This high luminous efficacy made them the preferred choice for urban street lighting, bringing bright nights to countless streets. However, the rapid development of science and technology has pushed the lighting field to innovate, and the rise of LED technology has broken the dominance of HPS street lights. According to the strict energy-efficiency standards set by the EU in 2021, LED lamps with “A” class energy-efficiency certification can exceed 210 lm/W, which is more than twice as much as the luminous efficacy of HPS street lamps, fully demonstrating the great potential of LED technology in improving luminous efficacy.
In practice, the high luminous efficacy of LED street lights has brought about significant energy savings. Take a 10-kilometer long road with street lights installed on both sides as an example, if a street light is installed every 30 meters, a total of about 668 street lights are needed. If the use of 400W HPS street lamps, the total power of 267.2kW; and the use of 250W LED street lamps, to ensure the same brightness, the total power of only 167kW, per year (according to the daily light 12 hours) LED street lamps can be compared to the HPS street lamps to save about 356,000 kWh of electricity, energy saving is very impressive.
In terms of circuit impact, there is also a big difference between LED street lights and HPS street lights; the power factor of LED street lights can be up to 95%, while that of HPS street lights is only 85%. Furthermore, LED street lights do not require ballasts like HPS street lights, and a 400-watt HPS street light requires a 34-watt ballast, which consumes a lot of power. In addition, the high harmonic content of the HPS street light circuit not only causes additional power loss, but also reduces the stability of the power grid.
In terms of light distribution, the efficiency difference between the two is also obvious. HPS street lamps need to use an arc reflector to focus the light on the road, a large amount of light is blocked or absorbed in the process, and the light output efficiency is only 65% – 70%. In contrast, LED street lights use a secondary optical lens to achieve a light output efficiency of up to 80%, and with a tertiary optical design, the efficiency can be further increased to 85% – 90%.
| Item | LED Street Light | HPS Street Light |
| Luminous Efficacy (lm/W) | Over 210 | 90 |
| Power Factor | 95% | 85% |
| Ballast Required | No | Yes |
| Light Output Efficiency | 80% (Secondary Optical Lens), 85% – 90% (Tertiary Optical Design) | 65% – 70% |
The cost difference between HPS and LED street lights is a key consideration in the replacement of city lighting. In terms of initial purchase price, HPS street lights typically cost $50 – $150, while LED street lights cost $200 – $500, with LED street lights costing about four times as much as HPS street lights. This significant price gap has deterred many cities from planning street light replacements, and has been one of the key reasons for the large-scale conversion of HPS street lights to LED street lights. However, with the continuous progress of LED technology, the production process is becoming more and more mature, large-scale production reduces the manufacturing cost, the price of LED street lamps is gradually reduced, and its market competitiveness is also improving.
solar led street light
In terms of installation costs, a 400-watt HPS street light draws more current than a 250-watt LED street light. This technical feature means that HPS street lights need to be equipped with thicker cables to meet their power transmission needs. When considering the large number of cables required for urban street light installations, this can add up to a significant additional cost. In contrast, LED street lights require a lower cable size, which can result in significant cost savings at the installation stage.
In terms of running costs, a 250-watt LED street light can achieve almost the same brightness as a 400-watt HPS street light, showing its energy-saving advantages. With 10 hours of lighting per day and an electricity cost of about $0.07/kWh, a 250-watt LED street light costs about $63.875 per year, compared to about $102.2 for a 400-watt HPS street light. In addition, LED street lights typically last 2 – 3 times longer than HPS street lights and have a slower light decay, eliminating the need for frequent replacement of bulbs, ballasts, and other components, which greatly reduces maintenance costs. In the long run, despite the higher up-front investment, LED street lights have a much lower life-cycle cost than HPS street lights due to the dual advantages of energy efficiency and low maintenance, resulting in significant cost savings.
| Item | LED Street Light | HPS Street Light |
| Initial Cost (USD) | 200 – 500 | 50 – 150 |
| Cable Requirement | Thinner | Thicker, Higher Cost |
| Operating Power
(for same brightness) |
250 W | 400 W |
| Annual Power Consumption
(12 hrs/day) |
1095 kWh | 1752 kWh |
| Maintenance Cost | Low | High |
| Lifespan | Over 10 Years
(12 hrs/day) |
1 – 2 Years |
LED street lights and HPS street lights have obvious differences in color temperature, which also determines their light color and lighting effect is different.LED street lights color temperature range is usually between 4500 – 5000K, belongs to the cool toned light, the light emitted is close to the white light, the spectrum is relatively wide, can cover a variety of colors of light. This broad spectrum makes LED street lights have a good color rendering index (CRI), generally between 70 – 80, which can more realistically restore the color of the object.
The color temperature of HPS street light is about 2100K, the light color is warm, showing obvious yellow. Its spectrum is relatively narrow, mainly concentrated in the yellow light region, which leads to the low color rendering index of HPS street lamps, only 23 – 25, the ability to restore the color of the object is poor. Under the irradiation of HPS street light, the color of the object will appear different degrees of distortion, especially for some brightly colored objects, this distortion phenomenon is more obvious.
solar led street light
In practical application scenarios, the warm yellow light of HPS street lights performs slightly better in long-distance road condition recognition at 90 – 160 meters, especially in foggy or dusty weather, and is suitable for fast lanes and main roads. For sidewalks, commercial pedestrian streets, residential areas and other roads, LED street lights with excellent color rendering, easier to identify pedestrian conditions, the advantage is obvious.
There are many misconceptions about the fog penetration of LED street lights. Visible light wavelength range of 380nm – 780nm, the range of light can be perceived by the human eye, LED street lamp spectrum than HPS street lamps more comprehensive, both have a peak at 580nm, but the blue part of the LED street lamps accounted for only 6% of the total luminous flux, the HPS street lamps are almost no blue light, and LED street lamps in the green – yellow region of the wider distribution of the light, the HPS street lamps in 2700 – 3000K, nowadays LED street lamps in the green – yellow region of the light distribution. The color temperature of HPS street light is 2700 – 3000K, nowadays LED street light has mature and excellent lighting effect in this color temperature range, and the problem of poor fog penetration caused by 5000 – 6000K color temperature in the early days has been solved.
HPS street lights are mainly composed of three parts: light source, electrical fittings (mainly ballasts and triggers) and lamps. In the actual use of these components, there are certain life limitations. the light source of HPS street lamps after a long period of time, there will be light decay phenomenon, that is, the luminous efficiency is gradually reduced, the brightness is weakened. Electrical components such as ballasts and triggers are also prone to failures due to prolonged operation and voltage fluctuations. All in all, the average service life of HPS street lights is only 1 – 2 years, and the service life of the lamps is also shorter. This means that frequent maintenance and replacement is required during the service life of the street light, which not only increases the maintenance cost, but also brings certain impact on the stability of urban road lighting.
In some high temperature areas, due to the high ambient temperature, the ballasts of HPS street lights are more easily damaged, and their actual service life is even less than 1 year, frequent maintenance and replacement brings great pressure to the municipal departments.
Compared with the traditional HPS street light, LED street light has obvious technical advantages, so that its service life has been greatly extended. LED street light adopts semiconductor light-emitting chips as the light source, this light-emitting method is different from the traditional thermal radiation light-emitting, with low energy consumption and less heat. At the same time, modern LED street lamps in the design of the heat dissipation problem is very important, through the use of efficient heat dissipation materials and reasonable heat dissipation structure design, can be timely LED chip heat generated by the heat emitted, effectively reduce the chip temperature, to avoid performance degradation due to overheating and shorten the life of the LED street lights.
solar led street light
Taking the LED street lights produced by some famous enterprises as an example, they can ensure that the service life of street lights reaches about 50,000 hours. Calculated on the basis of 12 hours of use per day, these LED street lights can last for more than 10 years. Longer service life not only reduces the frequency of street light replacement and maintenance, reducing maintenance costs, but also improves the stability and reliability of urban street lighting systems, reducing the impact of street light failures on traffic and residents’ lives. In some remote areas of the road lighting project, due to the inconvenience of maintenance, the long life of the LED street lamp advantage is more prominent, reducing the street lamp failure caused by lighting interruption problems, to protect the local residents of the night travel safety.
LED street lights have a very significant advantage – instant on. When the power is turned on instantly, the LED street light can immediately reach the full brightness state, this instant response characteristics make it in many application scenarios have a unique value. Especially in the field of security, LED street lights can be used in conjunction with motion sensors, when a person or vehicle is detected, the street light can be instantly lit to provide a clear lighting environment for the monitoring equipment, which effectively improves the monitoring effect of the security system. At the same time, in some roads or areas with irregular traffic flow, the instant-on function of LED street lights can also realize on-demand lighting, further saving energy.
Unlike LED street lights, HPS street lights need a longer warm-up time to reach full brightness after being turned on. Typically, it takes 5 – 10 minutes for an HPS street light to gradually increase from its initial brightness to its normal operating brightness. During this time, HPS street lights are not optimized for immediate illumination. This limitation of warm-up time limits the application of HPS street lights in some scenes with high demand for instant lighting, such as security areas that require quick response and roadway lighting that is frequently switched on and off.
In some emergency rescue channels, if HPS street lights are used, they cannot provide sufficient lighting immediately after being turned on in an emergency, which may affect the passage of rescue vehicles and the rescue work; while the instant-on characteristics of LED street lights can well meet the needs of emergency lighting.
Through a detailed comparative analysis of HPS street lights and LED street lights in five aspects: efficiency, brightness, cost, color temperature, service life and warm-up time, we can clearly see the differences between the two. Although HPS street lights have certain advantages in initial price and specific road lighting, from the perspective of comprehensive performance and long-term use, LED street lights show obvious advantages with their higher light efficiency, lower long-term cost, excellent color rendering, longer service life and instant-on characteristics. It is believed that in the near future, LED street lights will become the mainstream choice for urban road lighting, creating a brighter, energy-saving and comfortable night environment for us.
