The wattage of street lights can range from 30 W to 300 W, depending on different light sources and applications. Street light wattage is the first thing you will think about when choosing street lights. Street lights with the right wattage can not only provide bright illumination but also avoid energy waste. What should be the wattage of street lights for different applications? How to choose the wattage of HPS-equivalent LED street lights? How many watts will they consume? The following guideline on street light wattage contains all of the information you need!
How to convert the wattage of LED, HPS, fluorescent, and incandescent street lights?
| Light source | LED | HPS | fluorescent | incandescent |
| Light efficiency(lm/w) | 110 | 100 | 80 | 20 |
| Power factor | 90% | 85% | 85% | 100% |
| Light utilization efficiency | 90% | 60% | 60% | 60% |
| Light that passes through the housing | 90% | 60% | 60% | 60% |
Light utilization efficiency: Light sources have different light distribution designs. If the design is not reasonable enough, there will be light emitting outside of the roads or going in the wrong direction. As a result, the light utilization efficiency of this kind of street light is low.
From the table, we can determine the actual efficiency of the light sources:
LED: 110*0.9*0.9*0.9=80.19 lm/w
High pressure sodium: 100*0.85*0.6*0.6=30.6 lm/w
Fluorescent: 80*0.85*0.6*0.6=24.48 lm/w
Incandescent: 20*1*0.6*0.6=7.2 lm/w
The actual efficiency of LED street lights is 2.6 times higher than HPS lights, 3.3 times higher than fluorescent lights, and 11 times higher than incandescent lights.
Therefore, we can convert the wattage of HPS and LED according to their efficiency:
150 W HPS street lights≈60 W LED street lights
250 W HPS street lights≈100 W LED street lights
400 W HPS street lights≈150 W LED street lights
How many watts are street lights for different applications?
- Roadway street lights: For roadways, common street lights are 250 W to 400 W HPS street lights and 100 W, 110 W, 120 W, 150 W, 200 W, 250 W, and 300 W LED street lights. And the average wattage for street lights is 80 W. The roadways often carry heavy traffic, so the lighting standards are high. If applying HPS lights, the power needs to be high. But normally, LED lights are the better choice because of their high efficiency. They can achieve the same lux level at a lower power. Since the main roads and secondary roads have different traffic and standards, the lights for them have different wattage. For instance, the main roads may need 400 W HPS street lights, while 250 W HPS lights are enough for the secondary ones.
- Landscape/residential/rural street lights: Landscape street lights don’t need to provide very bright light, thus the wattage of LED street lights is generally 30-100 W.
- Industrial street lights: The LED street lights in common industrial parks are similar to those on city roads. Usually, they can be 6 to 8- meters -high, and the watts can be 50-100 W. But for special areas like the ports, they apply high mast lights, which can be 20 to 50- meters -high, so the wattage is also higher. The wattage of them can be 200-500 W.
How many kilowatts do street lights consume?
We can compare the most popular 400 W HPS street lights and their equivalent 150 W LED street lights to calculate how many kilowatts they will use in a year. Suppose the lights work for 10 hours every day.
HPS: 0.4 KW*10 H*365 D=1460 KWH
LED: 0.15 KW*10 H*365 D=547.5 KWH
How to calculate the right street light wattage?
We can apply the formula below to calculate the luminous flux and then divide it by the light efficiency of the street lights to determine the wattage.
F=Eav*W*S/(U*k*N)
F: Rated luminous flux, unit: lumen
Eav: Required average lux level for the lit area, unit: lx
W: Road width, unit: m
S: Spacing between street lights, unit: m
U: Coefficient of utilization factor, which is the ratio of the luminous flux that emits on the road to the total luminous flux the lights emit. It is affected by the elevation angle, height, road width, and placement of the street lights. The reference values are in the following form.
| elevation angle | 0° | 5° | 10° | 15° | ||||||||
| W/H | Behind the lamp | In front of the lamp | Total | Behind the lamp | In front of the lamp | Total | Behind the lamp | In front of the lamp | Total | Behind the lamp | In front of the lamp | Total |
| 0.5 | 0.25 | 0.36 | 0.61 | 0.2 | 0.35 | 0.55 | 0.18 | 0.34 | 0.52 | 0.15 | 0.32 | 0.47 |
| 0.6 | 0.27 | 0.4 | 0.67 | 0.22 | 0.39 | 0.61 | 0.2 | 0.42 | 0.62 | 0.17 | 0.41 | 0.58 |
| 0.8 | 0.3 | 0.47 | 0.77 | 0.26 | 0.46 | 0.72 | 0.22 | 0.48 | 0.7 | 0.19 | 0.47 | 0.66 |
| 1 | 0.32 | 0.53 | 0.85 | 0.28 | 0.54 | 0.82 | 0.24 | 0.56 | 0.8 | 0.21 | 0.55 | 0.76 |
| 1.5 | 0.36 | 0.55 | 0.91 | 0.31 | 0.59 | 0.9 | 0.26 | 0.63 | 0.89 | 0.22 | 0.64 | 0.86 |
| 2 | 0.37 | 0.57 | 0.94 | 0.34 | 0.62 | 0.96 | 0.27 | 0.64 | 0.91 | 0.23 | 0.69 | 0.92 |
| 2.5 | / | / | / | 0.63 | / | 0.67 | / | 0.71 | ||||
| 3 | / | / | / | 0.64 | / | 0.68 | / | 0.72 | ||||
| 4 | / | / | / | 0.65 | / | 0.69 | / | 0.73 | ||||
Note:
- W/H: The radio of the effective width of the road to the height of the lamp. The calculation of the effective width of the road is shown in table 1. The relation among the spacing (S), height (H), and effective width of the road (Weff) is shown in table 2.
- If the street light has an arm, the total coefficient of utilization factor equals to the sum of the values tested behind the lamp and in front of it.
| Length of the arm (XL, unit:m) ≤ 0.25H | |||
| Arrangement of the lamps | One-side | opposite | center |
| effective width of the road (Weff) | =Ws-XL | =Ws-2XL | =Ws |
Note: Ws: Actual width of the road, unit: m
| Light distribution | Cut off | Semi cut off | ||
| Arrangement of the lamp | H (m) | S (m) | H (m) | S (m) |
| One-side | H≥Weff | S≤3H | H≥1.2Weff | S≤3.5H |
| Staggered | H≥0.7Weff | S≤3H | H≥0.8Weff | S≤3.5H |
| Opposite | H≥0.5Weff | S≤3H | H≥0.6Weff | S≤3.5H |
Note: For curved roads whose radius is less than 1000 m, S should be calculated as 50%-70% of the straight line.
k: Maintenance factor. It is the ratio of the average illuminance on a certain surface of the lamp after a period of use to the average illuminance of a new lamp.
| IP rating | Maintenance factor |
| ≻IP 54 | 0.7 |
| ≤ IP 54 | 0.65 |
N: Street light arrangement coefficient. The street lights can be arranged in the way of one-side, opposite, and staggered, so the coefficient varies. When the street lights are arranged in an opposite way, N=2. For the other ways of arrangement, N=1.
For example, if we want to know the wattage of street lights on the main roads, we can first refer to the local lux level standard. (The standard varies for different countries.) Suppose the Eav should be 20 lx, the actual width of the road (Ws) is 15 m, the IP rating of the lamp is IP 54, the spacing (S) is 30 m, the height (H) is 12 m, the length of the arm (XL) is 1.5 m, the elevation angle is 15°, and the lamps are arranged in an opposite way.
We can infer that: k=0.65, Weff=Ws-2*XL=15-2*1.5=12m, N=2, and H and S comply with the standards mentioned above.
F=Eav*Weff*S/(U*k*N)=(20*12*30)/(0.72*0.65*2)=7692 lm
If the light efficiency of LED street lights can be 120 lm/watt, you will need 60-watt LED street lights.
Conclusion
From this comprehensive guide about street light wattage, you can learn how to convert the wattage of different light sources, the common wattage of the street lights in different applications, how much power the lights consume, and how to specifically calculate the wattage. After knowing the wattage you should choose, there are other things to consider, like the height, light distribution, etc. Check out our blogs for additional useful information, or contact us directly!
