What is light pollution
Light Pollution
The alteration of the natural quantity of light in the night environment due to the introduction of artificial light is a true pollution. “Pollution” means “impairment of the purity of the environment” (e.g. Mc Graw Hill Scie. Tech. Dictionary). Light pollution stands for “pollution of the light”: pollution of the natural light due to manmade light.
Light pollution produces many impacts on the environment and the health of the beings living in it (animals, plants and man), as shown by a large number of scientific studies and reports (see e.g. Rich C., Longcore T. 2005, Ecological Consequences of Artificial Night Lighting, Island Press). They are still little known because this field of studies has developed since few years. The growth of the night sky brightness is the most known of the many effects of light pollution only because it is the most evident and because astronomers, with their sensitive instruments, recognized it and begun to study it already many years ago, when it was not so pronounced. Even neglecting the many and well documented effects of light pollution on the environment, light pollution is a serious problem because it endangers the perception of the Universe around us, on which the starred sky constitutes the only window available for the population. A fundamental element for the culture, both humanistic and scientific, and one important part of the landscape patrimony is disappearing. Light pollution finally means energy and money waste.
Even considering only the effects on the night sky visibility, the situation of light pollution is particularly worrisome. From the impressive data available, it clearly appears that a legislative effort is indispensable in order to direct the progress and the development of the nighttime outdoor lighting in a virtuous way of respect of the environment and energy saving, which so far was not adequately undertaken. This legislative effort must be able to promote a change in the lighting habits and is demanded with urgency because light pollution grows in an exponential way, with growth rates that in some areas surpasses 7 per cent per year.  
What could be done?  The most natural and effective solution, that to shut off any external light, is obviously not practicable in the modern world where nighttime outdoor lighting is a social necessity. In a hypothetical scale of decreasing effectiveness, the second solution is to renounce to install any new lighting system. This would not eliminate light pollution but at least would set to zero its high yearly growth rate. This solution would not create the dark and it is seen positively from some peoples, however it could be conflicting with the development requirements of advanced industrial countries like ours. The third solution is to allow the increase of nighttime lighting but, at the same time, to enforce provisions to avoid that the light is wasted upward and a top limit to the yearly growth rates of the outdoor light flux installed in each town and to the yearly growth rates of the electric power consumptions for external lighting. These top limits favor the use of more efficient fixtures, the design of lighting installations with larger utilization coefficients and the use of lamps with larger efficiencies.
The best laws against light pollution currently in force in some Italian regions, undertook a more soft road, perhaps even too much soft (e.g. Lumbardy, Emilia-Romagna, Marche). They have chosen to not place any limit to the installation of lighting systems. Except few exceptions, everyone is free to illuminate whatever he wants. If a so wide freedom is allowed but at the same time a reasonably effective law in limiting light pollution is wanted, it must be required to follow at least some fundamental rules when designing and installing the lighting system. Any attempt to leave further freedom even on the rules, results is an ineffective law.
The basis of a truly effective protection is (i) the minimization of the direct light emissions over the horizon from the luminaires by a proper choice of fixtures and a proper lighting design, and (ii) the limitation to the minimum necessary of the light emissions reflected from the lighted surfaces, by avoiding over-lighting and containing at best the light wasted outside the area to be lighted.
The adverse effects of light pollution depend on the direction of the light emission. Upward light emission by fixtures and upward light reflection by lighted surfaces have typically a very different light distribution. Fixtures are usually the main responsible of the light emissions in those directions, which make light pollution propagate in a large area and add very efficiently with pollution produced from other sources. So upward emission by fixtures need to be minimized very accurately, particularly in the first 45 degrees over the horizon plane. See this paper to learn more.
Provisions to be adopted
Let’s resume the provisions to be adopted in an effective legislation against light pollution. Only the technical measures than cannot be renounced are listed here and only those already enforced and “experimented” somewhere. They should be part of a law and not postponed to following Regulations or Planes, because they should be stronger to win the resistances of the most unprogressive part of light polluters.
1) provisions should be applied in the entire territory without ineffective subdivisions in “protected areas” or poorly defined zoning because light pollution propagates very far from sources.
2) provisions need to be clearly applied to any NEW lighting installation, both public and private.
3) light pollution due to reflection by lighted surfaces should be limited by forbidding over-lighting and enforcing the use of flux reducers at the proper time or the shut off whenever possible. When a standard rule for safety exist, the average luminance or illuminance should not surpass the minimum value required for safety (e.g. road, walking areas, working areas). For other kinds of lighting a maximum luminance of 1 cd/m^2 should be permitted (e.g. building lighting).
4) limitation of direct upward emission produced by fixtures in any direction above the horizon, should be obtained by using a parameter depending on the direction of the light and not on the integrated light flux. A good parameter is the light intensity per unit of flux emitted by the light installation, in cd/klm. The light emissions at small angles above the horizon (the first 45 degrees) should be limited very carefully because they are the most effective in producing the adverse affects of light pollution.
5) the direct upward light emission of fixtures should be limited to 0 cd per 1000 lumens of flux emitted by the fixture, in any direction above the horizon (gamma angle equal or greater than 90 degrees) for almost any kind of lighting installation. A tolerance of 0.49 cd/klm is allowed in practice, because the limit is given as an integer number and then the measurements can be approximated to the nearest integer.
6) Building and monuments should be lighted from top to bottom, with the same limits given above for the upward lighting emissions, except in cases of proved impossibility (in this case it should be permitted to light from bottom but the border of the light beams should remain inside the boundaries of the lighted surface).
7) Lighting installations for large areas should complain to the same limits above (point 5).
8) Only lamps with the larger efficiency available for the requested use should be used. They save energy and produce less light pollution outside the photopic band and inside the scotopic band.
9) Upward directed light beams, beacons and similar luminous calls should be prohibited, even because they distract car-drivers and endanger the road safety.
10) Penalties for not compliant installations should be proportional to the number of fixtures.
11) The existing installations producing huge quantities of light pollution or belonging to the most polluting categories should be adapted.
12) The lighting design made by a professional lighting engineer should be mandatory for any lighting installation (except low power home installations with less than 5 fixtures). It should be completed with the photometries of fixtures in standard EULUMDAT format and a report demonstrating the numerical compliance with these rules.
The following prescriptions could also be added, whose precious effects of rationalization have already been pointed out: 1) the yearly growth rate of the installed light flux for nighttime outdoor lighting, public and private, in any municipal district cannot exceed the 2%; 2) the yearly growth rate of the electric power consumptions for nighttime outdoor lighting, public and private, in any municipal district cannot exceed the 1,5%; 3) the fraction of downward flux emitted by the lighting installation outside the surface to be lit should be accurately minimized as much as possible.
The limit on the yearly growth rate of the electric power consumptions for nighttime outdoor lighting has been recently enforced by law in some regions of Italy.
Courtesy of Giuseppe Peltran - GAS