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One of the important characteristics of these lights is the light distribution curve. The lights that are used in street lighting often have asymmetric light distribution due to the asymmetry of the street compared to the location of the lamp and the need to shine more of the lamp's light flux on the street surface. The light distribution curve is used to determine the intensity of light in different directions. Not all light sources are point, and to calculate the brightness, it is very important to know how the light is distributed. For this reason, the manufacturers provide the customer with the light distribution method along with the street lights .One of the important characteristics of these lights is the light distribution curve. The lights that are used in street lighting often have asymmetric light distribution due to the asymmetry of the street compared to the location of the lamp and the need to shine more of the lamp's light flux on the street surface. The light distribution curve is used to determine the intensity of light in different directions. Not all light sources are point, and to calculate the brightness, it is very important to know how the light is distributed. For this reason, the manufacturers provide the customer with the light distribution method along with the street lights .One of the ways to display the distribution of street lights is to use the polar light distribution curve. Since the distribution of illumination is usually symmetrical with respect to the vertical axis, the distribution of illumination can be checked by using a curve on a vertical plane. To check the distribution of light on the surface, the polar curve is a closed and usually asymmetric curve, and the distance of each point to the center of the plane indicates the light intensity at that angle. One of the disadvantages of using the polar light distribution curve is that if the changes in light intensity at different angles are large, the accuracy of the curve will be low .Street lights are divided into two categories, direct light and indirect (reflected) light, based on the way they emit light. Street lights with direct light are lights that all light reaches the surface from the lower hemisphere of the light. The table below shows the classification of lights based on how they emit light.

Light building: A street light is a device that distributes and transmits the light emitted by one or more lamps and includes all the necessary parts to support, install and protect the lamps; But auxiliary circuits and their connection devices to the power source are not included. According to this standard, the lights have different types that are classified based on their application and type of performance and installation. In this context, street lights are classified as fixed lights .Different parts of street lights

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 The bulb of the lamp must be of a type that can work continuously at the high temperature caused by the lamp. Also, in its construction, materials should be used that, when broken, turn into small particles with rounded corners, etc. Also, the ability of light to pass through the bubble should not be less than 0.85.Tungsten lamps, mercury lamps, sodium lamps and metal halide lamps can be mentioned among the main lamps used in street lighting. Of course, although tungsten lamps have low efficiency, they are used for ornamental applications. Also, due to the high efficiency and long life of sodium lamps, low pressure and high pressure sodium vapor lamps should preferably be used to provide street lighting.Low pressure sodium vapor lamps have high efficiency and produce yellow monochromatic light. The high-pressure sodium vapor lamp has a light with a combination of different colors, taking advantage of a longer lifespan. The use of low-pressure sodium vapor lamps is recommended only in traffic routes, where there is no need for light with a combination of different colors. In other roads, including roads passing through shopping centers and urban social and economic activity centers, etc., it is recommended to use high-pressure sodium lamps that have a suitable combination of light color. Mercury lamps have high efficiency and long life and are widely used in street lighting. These lamps are also divided into two categories of low pressure and high pressure lamps .Metal Halide lamps have good light color, good efficiency and long life and are used in areas where color clarity of objects is important. Fluorescent lamp, which is less used in road lighting today, has a relatively good light output, longevity and efficiency. One of the disadvantages of these types of lamps is their short life and the need for long lights and control devices.