Outdoor Lighting
| The New Zealand Energy Efficiency and
Conservation
Authority (EECA) have calculated that street and pedestrian
lighting annual energy consumption accounts for 21 million $(NZ), or
28% of an average Territorial Local Authority's (TLA) total energy
costs. Carbon Dioxide (CO2) emissions from electricity generation
associated with this end use are 25,900 tonnes per year. The survey
results received indicate that energy costs amount to $18.6 million per
annum, excluding state highway street lighting paid for by Transit New
Zealand. There appeared to be a wide range of practices in the area of street and pedestrian lighting,with small rural TLA's lacking the street-lighting engineering resources of the larger urban TLA's. In response the EECA, through the Energy-Wise Councils Partnership, and Transfund partnered this study to improve the understanding of the opportunities for cost effective improvements in street lighting. The EECA Street Lighting Energy Efficiency Study Other outdoor lighting includes signage, architectural and security lighting and floodlighting of carparks, buildings, monuments, schools and homes. At present, much of the installed outdoor lighting spills light beyond the area intended to be lit. The wasted light represents a waste of New Zealand's energy resources, and is having a significant impact on the visibility of the night time sky.  Figure 1 Figure 1 shows three possible designs for a standard street light fixture. The left hand image shows a street light with a flat-glass lens or full cut-off lamp. This design projects nearly all of the output of the lamp onto the area to be lit. No light is projected above the lamp, not into adjacent properties. The center image shows a similar lamp, but with a dropped refractor lens. This is also known as a semi-cutoff lamp. As shown the output from this lamp can disperse widely beyond the intended work area of the fixture. An estimated 30 to 40% of the light from this light will fall outside of the area intended to be lit, with much of this light interacting with aerosols in the atmosphere to produce sky glow. This skglow masks our view of the universe. The right hand image shows the typical situation in New Zealnd where the lamp is mounted at an elevetaed angle, approximately 15 degrees above horizontal. This worsens the effect of spilled light into the night sky. These lights are visible from many kilometers away. The EECA report on streetlight discusses a number of aspects of lighting but fails to mention this spilled light, nor the energy cost of this light. The City of Calgary in Canada has taken notice of this spilled light and replaced replaced many of its street lights with cutoff light fittings. The energy savings are significant. Calgary Street Lights
Figure 2 Figure 2 shows the difference between Non Cut-off, Semi Cut-off and Full Cut-off lights. By directing all the light from a lamp onto the required area, a lower wattage bulb can be used to achieve the desired lighting levels. 
Figure 3 
Figure 4 Figures 3 and 4 again display the savings that can be made. In this case a shield has been applied to the floodlight to direct the light on to the task area. The neighbouring property is protected from the direct output from the light and no direct light spills into the sky. For an excellent article on New Zealand's light pollution see the New Zealand Listener article of August 2003 Good Night by Rebecca Greatrex. |
