In the course of evolution, the human eye has adapted to bright, white sunlight. It is, therefore, not surprising that artificial white light is regarded as particularly natural. Despite this fact, high-pressure sodium vapor lamps were a preferred solution in street lighting for many years. Compared to the high-pressure mercury vapor lamps which were previously used, high-pressure sodium vapor lamps have a higher luminous efficacy and last longer. Their typically yellowish light, however, makes it difficult to distinguish colors at night and gives objects and buildings an unnatural effect. This is one reason why municipalities and lighting planners increasingly insist on white street lighting. More and more, the choice is becoming LED.
In the future, up to 80% of energy will be saved by the change to LED street lighting, compared to the high-pressure mercury vapor lamps previously in use. Even in the change from efficient luminaires, fitted with high-pressure sodium vapor lamps, to LEDs, distinct savings are possible.To a great extent, white LED light contributes to safety in the city. The luminous efficacy, ranging from good to excellent, and the subjectively greater brightness of white light contribute to the fact that objects, persons and buildings are more easily recognizable. Thus the number of traffic accidents, for example, can be markedly reduced. Investigations have shown that car drivers detect persons at the edge of the road earlier and from a greater distance away, when there is white street lighting. Pedestrians, too, recognize obstacles more quickly than under the yellowish light of the high-pressure sodium vapor globes frequently used in streetlamps.
The following is a further top benefit of white LED light: A decrease in the crime rate in cities is being achieved through the use of white light sources. Under this type of lighting, people are easier to recognize, potential crimes easier to detect and attacks easier for a third party to report. White light also enhances the quality of images from video surveillance systems and thus supports investigations by the authorities.
White is not always white. That is because, as is often the case in daylight, various color temperatures ranging from cold white to warm white are produced by artificial light. In public squares and in pedestrian malls, warm white light produces a comfortable atmosphere of well-being with color temperatures around 3,000 Kelvin. On the other hand, neutral white light promotes safety on the streets. As a result of a carefully selected color temperature, certain materials appear to better advantage in the architecture. For glass and steel, for example, a cooler light is chosen, whereas brick façades look more natural in warm white light.
