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The selection of lamps in road lighting design

Street lamps must be lit from dusk to dawn (about 4,000 hours per year), or from dusk to midnight, plus a period of time in the early morning (about 2,000 hours per year). Due to the high cost of electricity consumption and the high cost of checking and replacing bulbs, high-efficiency and long-life light sources are used. Low-pressure sodium lamps are generally used in urban streets and extra-urban traffic roads in the UK. Low-pressure sodium lamps have poor color rendering performance, but this disadvantage is alleviated by the lighting of shop windows and buildings such as cinemas. Street lamps in the city center require better color rendering, and color-corrected mercury lamps are generally used. Although fluorescent lamps and even incandescent lamps are still preserved after World War II, their number is not large. At present, the use of high-pressure sodium lamps in urban central areas is gradually increasing, and it is speculated that the application of metal halide lamps will also increase in the future. At present, in residential areas, low-pressure sodium lamps are increasingly replaced by color-corrected mercury lamps.

There is no consensus on what type of lamp to use for lighting in fog. Generally, in the surrounding bright fog, only the outline of the object can be seen, and its contrast decreases with distance and fog density. Different light source colors can show different contrasts, but due to the changes in light fog, it is difficult to draw a general conclusion on which color is best. In thick fog, street lamps can act as beacons to help vehicles move, but because the size of fog particles is similar to the wavelength of light waves, the transmission difference effect does not play any role, so the brightness and projection range of street lamps are definitely more important than color. The hazy image of the lamp in the fog is enough to distinguish whether the street lamp is on the left or right.

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