Accessibility and safety are two factors that make public lighting so important in our routine. First, to see and drive, which seems nearly impossible without her at night; Second, we need it to feel safe. If the light does not light enough, you may not see a hole in the street, the colors are not faithful to reality, trading closes early, people avoid getting stops in headlights.
In many cities, sodium lamps correspond to approximately half of all the lamps that there are on the streets, have a strong yellow color and not well maintain loyal the original colors of objects, because your color rendering index is approximately 20, when acceptable is above 60.
These indexes reflect an outdated technology in lighting that, despite having a good energy consumption, is not as efficient for the human night vision. Are effective only within the photopic vision (high light situation — which is not the case of the nocturnal environment).
As light levels, the human being sees differently at night. Brightness is assimilated differently before and after sunset, because our eye “adapting” as the sensitivity of these light levels. At night the human vision eliminates practically the entire spectrum of sodium lamp and recognizes better the colors Blue and green.
Metallic vapor lamps already have in your spectrum good levels of blue and green, so provide better visibility, in addition to greater energy savings if compared to the sodium vapour.
Metallic bulbs produce white light, have high colour rendering index (greater than 65, depending on the model) and a longer life and are more aware that the LEDs, for example. Through all this she continues to be an excellent choice when it comes to public lighting.