Street lights, the lights that you are so familiar with, have a long history. For centuries, they have changed in terms of shapes, materials, light sources, and so on. In this passage, we are going to introduce different types of street lights according to their light sources. The light source is the key to street lights, as it decides whether the street light can emit light that is up to standard, if the street light can be energy-saving, etc. Read this passage and find the best light source option for yourself!
1. Incandescent street lights
When people first used electricity as the power of the street light, they used incandescent lights, and that can date back to the 19th century. Incandescent lights generate light by heating the filament to an incandescent state. In this process, there will be heat radiation, which brings light.
- Uniform light: The light incandescent lights emit is uniform and soft, and the case can help the light emit in all directions.
- High CRI: The most obvious benefit of incandescent lights is that they have a very high CRI that can reach 95–97, which means that besides lighting up the objects, they can also reflect the actual appearance of them.
- Swift start-up: Once opened, their light output can quickly reach the rated value, so the incandescent lights don’t need much time to start working.
- Not safe enough: Because of its working principle, the surface temperature of the light is high; sometimes it can be up to 100 °C. If people touch them accidentally, they may get hurt. Moreover, the glass case will likely burst at high temperatures.
- Low efficiency: Most of the energy is transformed to heat by incandescent lights, so their efficiency is the lowest among all the light sources, which is 5-20 lm/W. Its low efficiency is the main reason why people don’t use incandescent street lights any more.
2. Low pressure sodium street lights
When the power is on, the temperature of low-pressure sodium lights increases, leading to the evaporation of sodium. With electricity, the sodium vapor emits visible light.
- High luminous efficiency: The closer the radiation spectrum is to the highest value (555 nm), the higher the luminous efficiency the light has. As the low-pressure sodium discharges radiation that is concentrated on Fraunhofer lines at 589 nm and 589.6 nm, its luminous efficiency is extremely high.
- Little color difference: Sodium sends out a radiation of a single yellow color. Therefore, it will cause less color difference compared to continuous or multi-line spectral radiation. Its high visual resolution will make the contrast between on and beside the road less obvious. This is especially important at places like the crossroads, the exit and entrance of the roads, etc., for avoiding accidents.
- Low CRI: Since sodium light produces a yellow color, it has a low CRI. So they are not suitable for places where people need to see things clearly.
- Slow start up: The solid sodium needs a high temperature to sublime. When the power is on, it will take a few minutes for the sodium to become sodium vapor, and the process can sometimes take 10 minutes.
3. High pressure sodium street lights
On the base of the low pressure ones, high pressure sodium street lights use both sodium and mercury to produce light. Thus, it can emit a light with a higher CRI, but still, the CRI is not as high as other types of street lights. Moreover, it also aims to fix weaknesses like the long discharge tube.
4. High pressure mercury street lights
High pressure mercury lights make use of the phosphor powder. When a high voltage is applied to the light, the low pressure mercury vapor will gradually turn into a high-pressure one. The high-pressure mercury vapor emits ultraviolet light, which makes the phosphor powder glow.
- Relatively high light efficiency: Compared with incandescent lights, their light efficiency is higher, which can be 35–65 lm/W.
- Cheap: The price of high-pressure mercury light is cheap, and it doesn’t cost much to maintain it.
- Ultraviolet light: The spectrum of the light emitted by the high pressure mercury light is discontinuous, and a large part of the light is ultraviolet and blue light, which may do harm to people’s health.
- Long start-up time: To reach the required high voltage, high pressure mercury lights need 4-10 minutes to start working. Besides, once it is closed, you will have to wait for it to cool down before using it again.
5. Low pressure mercury street lights
With lower voltage, low pressure mercury street lights have lower light efficiency than high pressure ones. And the light they emit has a spectrum that is not as wide as that of the high pressure mercury lights.
6. Metal halide street lights
On the base of high pressure mercury street lights, there is not only mercury but also metal halide in the light. When the air pressure in the light increases, the metal halide evaporates. The light it emits belongs to a different spectrum, so as to expand the overall spectrum and improve the CRI of the light to 70–95. However, the halides will have chemical reactions with each other and the glass at high temperatures. Metal halides are also easy to deliquesce, and the inhalation of a very small amount of water can cause abnormal discharge and blacken the lamp tube.
7. LED street lights
With the invention of blue-light LED bulbs, LEDs emerged as a new light source to produce white light. It emits light through the movement of the carrier in the light-emitting diodes.
- High light efficiency: After getting to know about the above types of street lights, you may find that most require a high temperature to emit light. This means that part of the electricity will be transformed into heat. But LED lights are not the same, so they can produce more light with the same amount of electricity.
- Long lifespan: LED’s feature of emitting a little heat makes it less likely to cause damage to the components of the light. So LED has the longest lifespan among all these lights.
- High price: Because of the high standards and high-quality materials LED lights use, the price of LED lights is higher. But it will save you money in the long run because of its high efficiency.
- Light decay: Sometimes after a long time of using LED lights, you may find them not as bright as before. The reasons can be the poor design of heat dissipation system or the choice of low-quality LED lights.
To choose high-quality LED lights, the best way is to choose reliable manufacturers like Mokolight, which has more than 17 years of experience. Here at Mokolight, you will meet a professional team of operators, salesmen, and engineers. The LED lights Mokolight produces are guaranteed by certifications like BSCI, UL, etc. Don’t wait; come find the best types of street lights at Mokolight!