Street lighting
Local authorities are not only responsible for the street lighting but also for the lighting required for squares, paths, building facades and Christmas illuminations. The focus in the following is on street lighting.
Standards
Regulations for outdoor lighting apply above all to street lighting. They define minimum levels of illuminance for safety, but no maximum values are specified.
In Austria, street lighting is not a specific legal requirement, but a duty to provide such lighting can be derived from various legal norms and court rulings (Austrian Civil Code, Highway Code, Supreme Administrative Court).
Basic provisions for street lighting are to be found in ÖNORM O 1051, ÖNORM O 1053 and in the European standard EN 13201.
DEN 13201 defines minimum illuminance (in lux) and luminance (in candela/m2). Specified illuminance is 25 lux for main roads and 3 to 10 lux on minor roads. Three lux is about ten times brighter than the light of the full moon.
- High pressure sodium lamp
- Light emitting diode (LED)
- Low pressure mercury lamp
- Metal halide lamps
- High pressure mercury lamp
- Luminaire with LEDs
Light-emitting diodes or LEDs are the product of a fast developing and sustainable lighting technology. Good quality LED street lights are now commercially available.
For environmentally friendly lighting, the colour temperature of the light sources must be low (3000 kelvin). Intelligent optic design is also important to ensure that the light is cast where it is needed and does not cause problems of glare.
PDF (Infoblatt "LED in der Straßenbeleuchtung")
High-pressure sodium lamps have a high luminous efficacy and emit a low proportion of UV light. The yellow light they produce enhances contrast sensitivity.
High-pressure mercury lamps, on the other hand, have the lowest energy efficiency and – thanks to the high proportion of UV light – the greatest power of attraction for insects. In accordance with EU regulation (EC) no. 245/2009, these lamps may not be sold after 2015.
Light fittings
Many conventional luminaires, like spherical luminaires and some standard street lights, radiate light in all directions. The light emitted upwards and sideways is not available for the intended purpose and constitutes a cost-intensive energy and power loss. It is also a major source of light pollution. That is why shielded light fittings, i.e. full cut-off luminaires, should be used.
Selecting a lower mounting height is an effective way of avoiding concentrations of light with long-distance effects. It reduces the amount of light emitted into the surrounding area and negative impacts on animal species. Typical pole heights vary between four and seven metres.
On sloping terrain, the street lighting should be located on the lower side so as to avoid unnecessary long-distance effects.
Efficient reflectors for targeted light control and flat diffusers are just as important as enclosed housings, which prevent insects from coming into contact with the lamps.
Operation
Intelligent lighting management can be employed to guarantee the availability of light when and as needed. |
The level of illumination should be reduced at night, when there is little traffic, from 11 p.m. to 5 a.m. say, taking due account of annual variations in daylight hours.
One option is single-lamp operation of twin-lamp luminaires after a certain point in the night. This solution must be provided for when planning the lighting system, with due attention paid to maintaining an appropriate distribution of light.
Another option is to include dimming circuits, so that the lamps can be dimmed to provide a reduced level of illumination. LEDs and fluorescent lamps are suitable for use with dimming circuits. Electronic ballasts can also be employed for stepless dimming with high-pressure vapour lamps at certain levels of illumination.
Potential for savings
Local authorities spend an average of 45 percent of their public electricity budgets on street lighting.
In view of the obsolete technologies employed in existing systems, there is a huge potential for savings in street lighting in terms of both electricity and the resulting costs and carbon dioxide emissions. |
The actual energy savings available vary depending on the types of light sources and fittings in use and those selected for the replacement scheme. The following figures are therefore only an approximate guide:
- Light sources: 30-40 percent
- Luminaires: up to 50 percent
- Operation: up to 30 percent
A lighting system upgrade on the basis of a complete replacement of light sources and luminaires is the most expensive solution, but it produces by far the best results with regard to energy and cost savings and general sustainability.
Project management and financing
In view of the wide variety of products available on the market and the differences between the various projects, it is essential to obtain advice from an expert, be it a lighting consultant or manufacturer.
It also makes sense to obtain advance information with regard to grants in aid.
Energy performance contracting is a frequently selected form of financing. In this case, the investment required to achieve savings in terms of energy consumption and maintenance costs is financed by a contractor. Basically, the contractor recoups the investment via the energy savings made over the period of the contract. Various forms of contracting are available today, and due attention must be paid to the conditions relating to maintenance, term of the contract, liability, compliance with the standards, and the guaranteed savings and other warranties, etc. That makes it meaningful to obtain independent advice.