In the mid 1900’s one of the primary goals of lighting was to help reduce the incidence of road accident, improve traffic flow and provide visual comfort for vehicle operators. By the early 1970s, high intensity light, in particular high pressure sodium vapor had become the pervading source of illumination in American cities, due to its high levels of illumination and long, reliable lifespan. Even with its benefits, the unattractive yellow-orange color made it difficult to distinguish colors in the area being illuminated. The unnatural orange tint of urban streets at night is something city dwellers had gotten used to through necessity rather than choice.
Beginning in the 1990s, city planners and architects began to question whether the over-use and misapplication of high-intensity roadway light sources was the best choice for city streets, parks, historic buildings and urban area lighting. Lighting designers pointed out that a footpath and a roadway, for example, with their differing surfaces, called for radically different lighting solutions, providing visual comfort and aesthetic sensitivity. At the beginning of the 20th century, incandescent street lighting was the preferred light source because of its sparkle, its white light and ability to render surroundings in truer colors. Advocates of the City Beautiful movement rejected efforts to explore more efficient, economical discharge light sources because “lighting must be made agreeable to the eye.”
Today, outdoor lighting applications are no longer confined to yellow light sources. Recent technological advances in metal halide, LED and fluorescent technologies are providing new alternatives that combine the qualities of daylight with the energy efficiency of high-pressure sodium lamps. This alternative is white light. As cities continue to grow and develop a marketable identity, the use of white light sources is becoming a key contributor in improving streets, public spaces and public life, creating a more livable community that residents are proud of and can relate to.
White light in urban residential and business settings offers many clear benefits when compared to yellow light:
Today’s advanced white light sources have equal or better energy efficiency than high pressure sodium.
Brighter perceived ambience, greater visibility and energy efficiency.
Improved color characteristics and color rendering. Colors appear more natural to the eye.
At the recommended illuminance levels for urban lighting, lower wattage alternatives can be use; they provide acceptable illuminance levels and lower energy consumption.
White light sources are perceived as brighter than yellow light at lowlight levels; it becomes possible to reduce overall light output while still giving users what they expect from the light source. UK lighting standards for exterior lighting now allow the minimum level of illumination on secondary roads and pedestrian walkways to be reduced as much as 30% (depending on the application) when the white light source used has a color rendering index of >60. or greater. 1
Increased visibility for motorists and pedestrians. White light improves drivers’ ability to see objects and roadside movement at a greater distance, i.e. a wider margin of safety.
White light helps people feel safer when moving around outdoors at night. Superior CRI, higher perceived brightness, makes it easier to distinguish objects, colors, people and facial recognition at a distance.
1 British Standard Code of Practice for Design of Road Lighting, BS489-1, 2003.
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