Why is the light from some street lights yellow/orange?
Lamps used for street lighting purposes are gas discharge lamps, which are much more efficient than the light bulbs you use in your house. The elements contained within the lamps give colour to the light emitted and the Lighting Engineer has a large choice of lamps from which to select. The low pressure sodium lamp is the most energy efficient, but has the drawback that its strong yellow/orange colour makes it difficult to tell the true colours of cars and other objects. High pressure sodium lamps emit a pale, honey coloured light, which gives better colour rendering of the street scene. More recent technological developments have produced discharge lamps which emit white light and as the efficiency and life expectancy of these lamps improves, they are likely to become the future choice for street lighting.
