In order to realize significant energy savings in the realms of lighting, light-emitting diodes (LED) became indispensable. This two-lead semiconductor light source is a suitable tool to make cities a bit more sustainable. Contrary to the popular opinion, LED’s are not only suitable to reduce the direct demand of electricity. Let us illuminate this subject with a best practice project – the switch to LED lighting in Milan, Italy.
LED lighting in Milan enables energy savings of about 50 %
To move closer, step by step, to a sustainable city, Milan has opted for a large-scale upgrade last year. 85,000 of the 141,000 street lights, provided by the Italian luminaire manufacturer AEC Illuminazione, require only about half the amount of lighting power due to the applied light-emitting diodes.
23,650 tons of CO2 less per year with LED lighting in Milan
According to the government of the Italian metropolis, savings of about €10 million can be achieved with the upgrade to LED streetlamps. The LED lighting in Milan transforms much more electricity into light. Former incandescent bulbs convert about 90 percent into heat instead of the envisaged light.
Further savings with dimming function
Lowering the brightness of a light can realize further energy savings. The luminous intensity can be controlled automatically depending on the surrounding illumination level. Using the so-called AstroDIM function, the luminaires are able to dim automatically in stages depending on an internal astronomical clock. It calculates sunrise and sunset times. Also individually programmed values can be applied.
Fewer maintenance expenses
The longer durability of LEDs leads to a reduced demand for conventional bulbs as well as fewer maintenance expenses for their replacement. LEDs are likely to last 100,000 hours. With an assumed lighting duration of 4,200 hours per year, LEDs can survive more than 23 years. And even if their lifetime is as half as much, they enlighten the streets of Milan much longer than HID bulbs with their 2-3 years. Consequently, the one year ago installed LED lighting in Milan needs 60,000 bulbs less every year. Frequently on and off switching does not affect the lifetime or light emission. By the way, LED technology brightens up immediately in contrast to traditional bulbs.
The excessive use of artificial light causes harmful light pollution. Cities are the main sources of this misdirected light competing with the night sky. To reduce this sleep-disturbing illumination, the light color and the control of the beam direction are two decisive influencing factors. LEDs are able to emit the luminous beam in a well-defined direction compared to conventional street lights using high-pressure sodium or mercury vapor. On the other hand, especially LEDs with high color temperature worsen the effect of light pollution which is demonstrated below with an example from Los Angeles. It is therefore recommended to install low blue content light sources like low CCT LEDs instead of white LEDs with high blue content.
However, white light can better pass through the fog. Vehicles become more visible. Furthermore, blue LEDs emit no ultraviolet light causing harm to human eyes or skin. Apropos sustainability: Efficient recycling opportunities for LEDs could make available rare materials which are manufactured. Indium and gallium inside the semiconductor diode and rare earths like europium or terbium in the phosphor could make a recycling process worthwhile.
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