Editing Light pollution (section)

===Improving lighting fixtures===

The use of ''full cutoff'' lighting fixtures, as much as possible, is advocated by most campaigners for the reduction of light pollution. It is also commonly recommended that lights be spaced appropriately for maximum efficiency, and that number of luminaires being used as well as the wattage of each luminaire match the needs of the particular application (based on local lighting design standards).

Full cutoff fixtures first became available in 1959 with the introduction of [[General Electric]]'s M100 fixture.<ref name="AM-Feb2009-57">{{cite journal|last=Bakich|first=M.E.|date=February 2009|title=Can we win the war against light pollution|journal=[[Astronomy Magazine]]|page=57|issn=0091-6358}}</ref>

A full cutoff fixture, when correctly installed, reduces the chance for light to escape above the plane of the horizontal. Light released above the horizontal may sometimes be lighting an intended target, but often serves no purpose. When it enters into the atmosphere, light contributes to sky glow. Some governments and organizations are now considering, or have already implemented, full cutoff fixtures in street lamps and stadium lighting.

The use of full cutoff fixtures helps to reduce sky glow by preventing light from escaping above the horizontal. Full cutoff typically reduces the visibility of the lamp and reflector within a luminaire, so the effects of glare are also reduced. Campaigners also commonly argue that full cutoff fixtures are more efficient than other fixtures, since light that would otherwise have escaped into the atmosphere may instead be directed towards the ground. However, full cutoff fixtures may also trap more light in the fixture than other types of luminaires, corresponding to lower luminaire efficiency, suggesting a re-design of some luminaires may be necessary.

The use of full cutoff fixtures can allow for lower wattage lamps to be used in the fixtures, producing the same or sometimes a better effect, due to being more carefully controlled. In every lighting system, some sky glow also results from light reflected from the ground. This reflection can be reduced, however, by being careful to use only the lowest wattage necessary for the lamp, and setting spacing between lights appropriately.<ref>[http://www.rpi.edu/dept/lrc/nystreet/ NYSERDA How-to Guide to Effective Energy-Efficient Street Lighting for Planners and Engineers.] {{Webarchive|url=https://web.archive.org/web/20110102010555/http://www.rpi.edu/dept/lrc/nystreet/ |date=2011-01-02 }} NYSERDA-Planners (October 2002). New York State Energy Research and Development Authority.</ref> Assuring luminaire setback is greater than 90° from highly reflective surfaces also diminishes reflectance.

A common criticism of full cutoff lighting fixtures is that they are sometimes not as aesthetically pleasing to look at. This is most likely because historically there has not been a large market specifically for full cutoff fixtures, and because people typically like to see the source of illumination. Due to the specificity with their direction of light, full cutoff fixtures sometimes also require expertise to install for maximum effect.

The effectiveness of using full cutoff roadway lights to combat light pollution has also been called into question. According to design investigations, luminaires with full cutoff distributions (as opposed to ''cutoff'' or ''semi cutoff'', compared here)<ref>{{cite web |url=http://www.eskimo.com/~jrterry/optics.html |title=Optics for Streetlights |publisher=Eskimo.com |access-date=2010-09-04 |archive-url=https://web.archive.org/web/20100915083231/http://www.eskimo.com/~jrterry/optics.html |archive-date=2010-09-15 }}</ref> have to be closer together to meet the same light level, uniformity and glare requirements specified by the [[Illuminating Engineering Society of North America|IESNA]]. These simulations optimized the height and spacing of the lights while constraining the overall design to meet the IESNA requirements, and then compared total uplight and energy consumption of different luminaire designs and powers. Cutoff designs performed better than full cutoff designs, and semi-cutoff performed better than either cutoff or full cutoff. This indicates that, in roadway installations, over-illumination or poor uniformity produced by full cutoff fixtures may be more detrimental than direct uplight created by fewer cutoff or semi-cutoff fixtures. Therefore, the overall performance of existing systems could be improved more by reducing the number of luminaires than by switching to full cutoff designs.

However, using the definition of "light pollution" from some Italian regional bills (i.e., "every irradiance of artificial light outside competence areas and particularly upward the sky") only full cutoff design prevents light pollution. The Italian [[Lombardy]] region, where only full cutoff design is allowed (Lombardy act no. 17/2000, promoted by [[CieloBuio|Cielobuio-coordination for the protection of the night sky]]), in 2007 had the lowest per capita energy consumption for public lighting in Italy. The same legislation also imposes a minimum distance between street lamps of about four times their height, so full cut-off street lamps are the best solution to reduce both light pollution and electrical power usage.<gallery mode="packed">
File:LED Droplight.JPG|alt=This kind of LED droplight could reduce unnecessary light pollution in building interiors.|This kind of LED droplight could reduce unnecessary light pollution in building interiors.
File:Flat-lens cobra luminaire.jpg|alt=A flat-lens cobra luminaire, which is a full-cutoff fixture, is very effective in reducing light pollution. It ensures that light is directed only below the horizontal, which means less light is wasted by directing it outwards and upwards.|A ''flat-lens cobra luminaire'', which is a full-cutoff fixture, is very effective in reducing light pollution. It ensures that light is directed only below the horizontal, which means less light is wasted by directing it outwards and upwards.
File:Drop-lens cobra luminaire.jpg|alt=This drop-lens cobra luminaire allows light to escape sideways and upwards, where it may cause problems.|This ''drop-lens cobra luminaire'' allows light to escape sideways and upwards, where it may cause problems.

File:110101 LightPollution Italian Regional bills specs.jpg|alt=The majority of Italian regions require "zero upward light", which usually implies the use of overall full cut-off lamps for new luminaires, but violations are common.|The majority of Italian regions require "zero upward light", which usually implies the use of overall full cut-off lamps for new luminaires, but violations are common.
</gallery>