A series of tests have been conducted at the Lighting Research Center in Troy (New York) on the human perception of nighttime street lighting.

In a comparison between a high pressure sodium street (HPS) light system at 15 lux and a white LED light system at 5 lux, for 70% of the interviewees the LEDs gave a more natural and authentic effect to the environment.

The perception of safety was unchanged, even though the level of brightness the LED lights was about 30% lower than that of the HPS system.

Our sensitivity to light depends on the retina, made up of rods and cones, which interprets the frequency of light spectrum as tending towards light (yellow) or dark (blue).

If a light source is made up of higher levels of blue light emissions, it will be picked up more readily by the rods (associated to nighttime brightness). This source, therefore, does not have a higher emission level, but emits a high percentage of light frequencies perceived by the human eye.

Thus, by reducing the brightness levels of white light (LEDs at 5 lux), it is possible to keep the level of perceived brightness constant whilst reducing energy consumption.

BENEFITS:

• better aesthetic perception of the environment;
• better definition of faces by CCTV cameras;
• less road accidents;
• energy and money saving.