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\title
{Measurement of the light pollution:
 a project for the Grant Agency of the Czech Republic}
\authJHPP
\date{March 28, 2002}

\maketitle

The growing light pollution has damaged our twilight and nighttime
environment in the last decades to a very large degree.  Whereas the
implication for the night sky is obvious (qualitatively at least), the
consequences for the outdoor safety and visual bearings of people, for
their health and for wildlife are just becoming to be studied. 


\subsection
{Background}

An ever increasing part of the public becomes aware that the consequences
of poor outdoor lighting are really serious, and that the lighting can be
easily improved a lot and at low (mostly even negative) costs.  In many
places throughout the world the lighting has been reconstructed to be less
polluting and obtrusive, demanding less power (and contributing less to
the greenhouse emissions). In some municipalities, regions, and states,
such efficient lighting is demanded by the law already. 

Czechia has joined these pioneers them recently.  A requirement to prevent
the light pollution is a part of its Act on the Protection of the
Atmosphere. In fact, it's the first nation-wide case in the world -- legal
prevention of light pollution is being prepared in another countries
(e.g., Italy, Slovenia, Croatia), but Czechia became the first one. This
is undoubtedly a result of a strong position (and popularity) of astronomy
research and education in our country, and of the fact, that the leading
Czech astronomers acted as responsible citizens during the preparation of
the law.  While prevention of the light pollution is a general
environmental issue, astronomers with their intimate knowledge of the
night environment are naturally the first part of the society which
realized the degree of the problem and worked on solutions. In the regions
with longer history of prevention of poor lighting, they have allies from
numerous fields (biology, medicine, police, ...) -- including lighting
engineers. In Czechia such process is still in its infancy but thanks to
the new law, to the broad public interest (and to many journalists), the
public perception of the seriousness of the problem grows quickly. 

The Czech law (valid since June 1, 2002) says (see
\h{www.astro.cz/darksky}) that 
     ``light pollution [is] every form of illumination by artificial light
       which is dispersed outside the areas it is dedicated to,
       particularly, if directed above the level of horizon.''

Being a qualitative definition, the statement in the law is clear enough. 
Primarily the direct light from lamps radiated above the horizon should be
avoided, as it is technically feasible and common in many places already.
However, it would be highly interesting to have quantitative data on the
degree of light pollution as well. There is a unique opportunity to
document, how the pollution is diminished with application of the rules
demanding proper use of outdoor artificially produced nighttime light. 

The first task is to quantify the present state.


\subsection
{Astronomical photometry}

A part of it can be done through the proper use of standard astronomical
photometry: in fact, the luminance of the sky is computed routinely during
astronomical photometric measurements of celestial objects.  To study the
level of light pollution of the sky, the sky luminances (or radiances in
the corresponding filters) should not be discarded after completing the
reduction of the astronomical object's data, but it has to be recorded and
published. This holds for the new observations as well as for old archived
data. A call for such data came several times already from Pierantonio
Cinzano, the lead author of the new classic ``The first world atlas of the
artificial night sky brightness''. Artificial contributions to luminances 
of the sky (or their infima
in zenith) have been computed for most of the world by his group based on
the satellite images of cloudless nighttime Earth. However, a validation
through the Earth-based direct measurements is scarce and much needed.
In Czechia, with a
dense network of people doing astronomical photometry, such validation can
be made with a moderate effort.

Using the standard photometric data for that purpose assumes that the
needed software will be developed, a simple-to-use one. This is one of the
goals of the project. The software will be then published with its first
results and all the people doing astronomical photometry could consider to
use it and either publish the results or make them available to others. 
The basic version of the software will extend the astronomical image
processing software Munipack (see \h{munipack.astronomy.cz}), but
another standard photometric packages should also get an option to report
sky radiances. 

Another goal is to do dedicated measurements of the night sky luminance
both in remote locations far from the artificial lighting and in selected
areas of high level of light pollution, observing zenith and selected most
interesting azimuths at various elevations above horizon. Such remote
sites are most influenced by the direct just-above-horizon light from the
lamps and should reclaim almost pristine skies when the lighting is made
as non-polluting as possible in the future. A new portable equipment is
necessary for this research.  A straightforward method of the calibration
of the measuring device can be developed from the method of classic CCD
astronomical photometry.


\subsection
{Terrestrial photometry}

The same equipment (an over-8-bit digital camera, a notebook and further
accessories) will be then used for terrestrial imaging of nighttime scenes
as well. One goal is to view the same locations (settlements, industrial
areas) at different angles down from the horizon. The amount of direct
polluting light from the lamps will be quantified this way and its
proportion to other light measured (from, e.g., the illuminated surfaces,
windows, neon advertisements, car headlamps).  This proportion is largely
unknown -- simple looks from hills and towers down to the inhabited
nighttime area shows that poorly aimed lamps are vastly dominant, but some
advocates of the current public lighting practice still claim that the
role of direct light from street and area lighting is minor.  Thus, there
is a need to measure their actual contribution. 

In some cases, the same area should be investigated at various downward
angles, to study the angular dependence of the upward going light -- a key
issue for the computation as made for ``The first world atlas ..'' and
previous works, but a rather uncertain one. An plane flying over the area
should serve for this purpose while a series of images would be taken from
its bottom. 

The two tasks mentioned above concern the sources of the artificial
contribution to the nigh sky luminance, i.e. the original ``astronomical''
concern about light pollution. However, even other polluting (and directly
obtrusive) light should be investigated. 

Illumination of the interiors of the sleeping rooms by poorly aimed lamps,
nighttime advertisement or excessively lit surfaces should be measured as
well, with the same imaging system and with some calibration tools (common
to all terrestrial measurements, i.e., with high-sensitive meters of
illumination and luminance). 

Finally, the street and area lighting from the perspective of pedestrians
and drivers will be investigated. The illumination and luminances of those
surfaces, which are lit on purpose as well as of those, which should not
be lit at all, will be measured and compared with the direct light from
lamps in the field of view. Glare from the lamps and overly lit billboards
will be quantified and compared with human judgements (of people with and
without sight disabilities). 

For making and evaluating terrestrial photometry, a new technique and
software will have to be developed. Curiously, a part of the evaluation
can be done by using a sw for astronomical photometry. Namely the distant
lamps are behaving like stars and their brightnesses can be computed in a
similar way just like the brightnesses of celestial objects. What remains,
the background, is like a sky containing some nebulosities. Again, a
software will be sought for (or developed), that will enable other people
worldwide to pursue the same tasks. 

Apart from using the most adequate hardware for terrestrial photometry, a
possibility to get useful results with most common digital cameras will be
investigated. It can be however supposed that the capabilities of common
cameras on the market will grow over the next years, so what will be
developed for the most advanced today-ones, may be immediately useful for
many other types in the near future. 


\subsection
{Documenting the expansion of quality outdoor lighting}

In some areas, the old polluting lamps are being replaced by less
polluting ones. The improvement achieved this way will be documented for
some cases. Even more important is the documentation of changes within the
pilot areas around major observatories (or perhaps nature reserves), where
the improvement of outdoor lighting is envisaged (by the law and the
proposed implementing regulations demanded by the law) even before the old
lamps die of age.  Even though such adaptations and replacements of old
lighting systems will be cost-effective in most places, inevitably they
need some initial investment. The investors will naturally ask: how much
has the light pollution diminished?  The quantitative answer could and
should exist and be published, and the procedure how anybody can get such
results should become quite clear, so that it could be used by lighting
engineers too. 

\subsection
{Collaboration}

The whole topic is rather new. The applicant is well acquainted with the
field's state of the art and is in contact with most researchers at this
field (and with some in related fields) in the world.  As a person
contributing to the adoption of the anti-light-pollution legislation in
Czechia, he feels that the newly emerged leading role of his country at
this field should be pursued further, with scientific (rather than just
educational, as it was up to now) goals. Of course, an educational
outreach and publicity of the results will be pursued as well. 

The current project can in many aspects of investigation methods use the
results of another project supported by the Grant Agency of the Czech
Republic, namely that one by Petr Baxant, ... and can proceed partly
side-by-side along it. New people, students, astronomers and lighting
engineers will be engaged for the investigation of consequences and
remedies of outdoor lighting.  In future the research may expand to
another countries as well, some international cooperation may emerge even
during the project. 

Linking the measured photometric quantities (mesopic, twilight-seeing
photometry will be pursued as far as possible apart from a standard
photopic, daytime-seeing one) with the health effects, traffic accidents
rate, birds behaviour etc. is also possible, but difficult to plan. Some
research of this kind is probable to emerge (in case of the ecological
consequences of nighttime lighting, people participating at the conference
of that name are promising collaborators, see
\h{www.urbanwildlands.org}, as well as some Czech zoologists interested
in this new field). Our project welcomes interdisciplinary cooperation,
but will concentrate on photometry itself. 

The running results will be publicly available on Internet and the major
achievements published on the conferences and in the scientific press. 

A by-product may be photometry of bright stars, which is anyway necessary
for getting the values of the actual extinction of light by the atmosphere
-- knowing the extinction coefficients enables using all luminance data,
not just their infima, to know the magnitude of light pollution. 


\subsection
{The main participants}

The applicant, Jan Hollan, works at the N. Copernicus Observatory and
Planetarium in Brno. He is the sole Czech member of the International Dark
Sky Association (honored by an award from its executive director recently,
for his achievements at the promotion of non-polluting lighting and his
contribution to legal framework in Czechia), a founder and leader of a
Czech group of dark sky advocates. He has advised at photometry tasks his
students a long time. He has written a lot of astronomy software,
including a programme for evaluating the ``sky light pollution increment
of luminaires'' (see \h{amper.ped.muni.cz/light/ies2}). The
Observatory itself is doing astronomical photometry with a standard
CCD+telescope equipment at two sites (Brno and Vyskov) and its data are
among those to be processed (including the new ones acquired directly for
this purpose). 
 
The co-applicant Petr Pravec is doing photometry at Ondrejov Observatory
of the Astronomical Institute of Academy of Sciences of the Czech
Republic. He leads a team investigating minor planets, esp. the Near Earth
Objects. Reducing light pollution of the sky is a vital issue for his
research in Ondrejov, the long series of the old and new data will enable
documenting the reversal of the trend from getting worse to getting
better. The standard equipment for astronomical photometry in Ondrejov is
the best one in Czechia and it is in a continuous operation since 1994.

The collaborator Petr Baxant is evaluating luminance information from
digital images with respect to glare and visual comfort.  His expertise
will add much to the calibration and evaluation of outdoor terrestrial
photometry. Through his Department of Electrical Power Engineering,
Faculty of Electrical Engineering and Computer Science at Brno University
of Technology he is able to share some equipment for initial
investigation to help in choosing appropriate hardware for the project. 


\bigskip\noindent
Jan Hollan, March 2002

\begin{thebibliography}{9}
\bibitem{C1} Cinzano, P.  2001: private comm., 
 \h{amper.ped.muni.cz/jenik/letters/public/msg00022.html} 
\bibitem{C2} Cinzano, P. -- Falchi, F. -- Elvidge, C. D. 2000: 
 The first world atlas of the
 artificial night sky brightness, Monthly Not. of Royal Astron. Soc, 328,
 689-707,  see also \h{www.lightpollution.it} (also for further papers
 of Cinzano) 
\bibitem{C3} Cinzano, P. 2000: 
 The growth of light pollution in north-eastern Italy from 1960 to 1995,
 in Measuring and Modelling Light Pollution, ed. P. Cinzano, Mem. Soc.
 Astro. It., vol.71, 159-166 (2000) - submitted April 1998
\bibitem{C4} Cinzano, P. 2000:
The Propagation of Light Pollution in Diffusely Urbanised
Areas, in Measuring and Modelling Light Pollution, ed. P. Cinzano,
Mem. Soc. Astro. It., vol.71, 93-112 (2000) - submitted May 1998
\bibitem{B1}
Baxant, P:
 Luminance distribution analysis using digital photography,
 PhD thesis, Brno 1999, for
 a pdf summary see \h{bear.ro.vutbr.cz/nakl/thesis/baxant.pdf}
\bibitem{H1}
 Hollan, J. 2001: Let's illuminate just that, what we really want to
(a leaflet, in Czech), Czech Astron. Society, for a crude English draft see 
 \h{amper.ped.muni.cz/light/zakon_oo/letak}

\end{thebibliography}


\end{document}
