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09.07.2012
 

LED street lighting saves energy and is environment-friendly

LED lighting

Source: OSRAM Opto Semiconductor

Experts estimate an energy saving of 7.5 billion kilowatt hours for private lighting, 8.3 billion kilowatt hours for industrial lighting and 3.2 billion kilowatt hours for office lighting. With 2.2 billion kilowatt hours, street lighting also offers significant power saving potential, because about a third of Germany’s street lighting is at least 20 years old. Modernisation would not only drastically reduce CO2 emissions, but also help to cut costs over the long term.

There’s another reason why municipalities need to take action. They are under an obligation to provide street lighting. The EU Ecodesign Directives 2005/32/EC and 2008/28/EC prohibit the sale of mercury vapour lamps starting from 2015.

Luckily, for some time now LEDs have provided an economical alternative lighting solution. LEDs offer enormous flexibility for indoor and outdoor lighting. A long life, low energy consumption, low maintenance costs, easy dimming and resistance to knocks and vibrations are the trademarks of the new lighting systems.

How street lighting has to be designed is defined in DIN norms, e.g. in DIN EN 13201 Part 1, which regulates the selection of lighting classes. The lighting situations to be examined for different traffic areas are described using a parameter system. The basic parameters are the typical speed of the main user – high, medium, low speed or walking pace – and the types of user within the area under examination, for example motorised vehicles, bicycles or pedestrians. Depending on the combination of the individual basic parameters, this results in a lighting situation, which is described with a letter and a digit. Further parameters, such as the geometrical properties of the traffic area and the prevailing weather, are also taken into account and ultimately produce the lighting class.

Municipal decision-makers also have to keep an eye on the useful life of lighting systems. Here LEDs generally score very high if all the parameters are correct. A long-lasting system will depend on how well the thermal management of the LEDs has been designed. The barrier layer temperature is a very important variable for LEDs. High-performance LEDs do not emit heat with the light, in contrast to conventional light bulbs. The heat generated inside the LED has to be removed from its back via materials that have high thermal conductivity, like metallic or ceramic elements, thermal pads to the board and to the surroundings.

It is not only the service life that depends on the temperature of the barrier layer, but the optical properties, such as colour or light intensity, are also affected. Precise knowledge of this variable, which is also referred to as the junction temperature, is of great importance in practice. A widespread, but relatively inexact method is measurement with a thermal imaging camera. Some suppliers use more precise measuring techniques, which are thus more reliable, to determine the temperature of the barrier layer, while at the same time measuring further key parameters such as light intensity and power consumption.

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