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\title{\vspace{-3cm}Report on activities 
of the \wwwt{Czech Section}{http://www.astro.cz/darksky}
 of the International Dark Sky Association
in 2004 and 2005}
\author{\wwwt{Jan Hollan}{http://amper.ped.muni.cz/jenik}}
\date{January 30, 2006}

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\section{Summary}

In 2004 and 2005, the Czech section of the IDA worked quite a lot on 
legislation and education, but the main activity was the  research. Due
to ``demand side'', most outputs are available in Czech  only. The
occasional English remarks are linked to in the following text. Let's 
remember that our main info in English is at \h{www.astro.cz/darksky} 
-- unfortunately not at all so up-to date, as this Report tries to be.

\section{2004}

The first half of 2004 has been mentioned in our previous report 
already, 
   \emph{Czech IDA section report on 2003}
   \h{amper.ped.muni.cz/jenik/letters/public/msg00220.html}, 
namely the results of our research -- they have been 
published in winter of that year. Some minor corrections within the main 
report and its parts have been made since and the directory 
\h{amper.ped.muni.cz/noc/} updated accordingly. The state of our 
knowledge at that time and future research goals are summarised within 
our (unsuccessful) grant application, available as (pdf is there too)    
\emph{Light as a Pollutant of the Night Environment: reality,impacts, 
remedies. Description and Substantiation of the        Project submitted
to the Czech Science Foundation} 
\h{amper.ped.muni.cz/noc/english/res_plan2004.html}.


\subsection{Health damage from man-made light at night}

In April 2004, we have submitted four abstracts 
(\h{amper.ped.muni.cz/noc/english/Can_and_Rhythm.htm})
to the Cancer and 
Rhythm conference to be held in October. 
They have been accepted as posters (all oral presentations were invited ones). 

In August, I was invited to  participate in an:   
 \emph{International Scientific Conference on Childhood Leukaemia
 -- incidence, causal mechanisms and prevention,
 Westminster, London, 6 - 10 September 2004}
  \h{leukaemiaconference.org/}.


I prepared a poster summarising our research results, its abstract is 
  \h{amper.ped.muni.cz/noc/english/leuk_conf/cz_light.htm}, 
 the very poster being 
  \h{amper.ped.muni.cz/noc/english/leuk_conf/post_jh.pdf}. 
It appeared I was the only participant concerned with general
protection of night environment against man-made light; however, many
participants were concerned with possible causal link between too much
light and childhood leukaemia, and the key researchers at the field
issued serious warnings in the media, see the conference pages or my 
posting
   \emph{Articles on Childhood Leukaemia}
    \h{amper.ped.muni.cz/darksky/2004/000069.html}. 
 For me, the most  convincing paper was by Sam Milham, on the rise of
incidences a few  years after electrification in the US (our
interpretation differs from  his: not 60 Hz magnetic field, but rather light at
night is the probable cause). I've exchanged two letters on this with
Ken Campbell, the very paper is  hyperlinked to at the end of the first
one:  \h{amper.ped.muni.cz/jenik/letters/public/msg00149.html}, 
      \h{amper.ped.muni.cz/jenik/letters/public/msg00150.html}.

Shortly after the conference, mentioning it within 
    \emph{[DSLF] Digest Number 1449}
    \h{amper.ped.muni.cz/jenik/letters/dsa/msg00068.html}
 I was asked by David Keith to propose a formula for 
metabolic-efficient light. So I did, announcing it within
   \emph{"Cancer and Rhythm" -- please register}
   \h{amper.ped.muni.cz/darksky/2004/000068.html}

The formula has been presented at the next conference in Graz, three of 
our four posters are inside  
  \h{amper.ped.muni.cz/noc/english/canc_rhythm/}
 (the remaining one, on blood pressure is not online). Our poster 
\www{g_camer.pdf}
{http://amper.ped.muni.cz/noc/english/canc_rhythm/g_camer.pdf}  was not
the only one devoted to measuring  metabolic-efficient light, but the
only one showing how to measure them  with common digital cameras,
mentioning the tolerable  levels and the need and ways of filtering out
the shortwave half  of the spectrum.\footnote{In the poster, some
imaging photometry examples from the London conference are shown; I have
made available all examples including both photopic and 
metabolic-efficient photometry just now, see
\amper{light/luminance/london}.}
One of another posters gave a reference to 
the smooth action spectrum curve proposed earlier already (based on 
papers from just two teams, not all the three ones), within
   \emph{Gall, D.:
   Die Messung circadianer Strahlungsgr��en.
   Tagung Licht und Gesundheit 26. bis 27.2.2004 Berlin}
\h{www.tu-ilmenau.de/site/lichttechnik/fileadmin/template/fglt/publikationen/2004/Vortrag_Gall2004.pdf}

Two of our posters were devoted to another aspects of light than to 
reducing melatonin production: rising the blood pressure and  disturbing
sleep. The last one alone is a serious reason for urgent  adaptation of
all outdoor lighting. 

Thomas Posch (Austrian IDA section) wrote a 
 \emph{Graz conference report},
 \h{amper.ped.muni.cz/jenik/letters/public/msg00183.html}

(Since October 2004 we filter out shortwave half of light at night at 
home, using either pure yellow linear fluorescents, yellow glass paint 
or yellow self-adhesing, well translucent foil. It's a pleasure to 
everybody, being really cosy,
and in fact inevitable for your good conscience, if
you become aware that light at night becomes a poison at most common 
indoor levels but the lowest ones.)


\subsection{Monument lighting and the limits for it}

The case of Boston Stump church lighting, which damages the night view of 
England (raised by Darren Baskill within the CFDS forum), moved me to 
study this phenomenon further. The result is surprisingly simple: any 
church illuminated to levels over 1\cdpms{} becomes an unpleasant 
dominant when seen from the space (of course not the church, just the 
lights around it). See the most relevant letter,
   \emph{Earth from above (continuing ``for your
          amusement'')}
\h{amper.ped.muni.cz/jenik/letters/public/msg00152.html}:

\begin{quote}
 ``Moreover, a general conclusion follows: any luminance higher than 
one candela per square metre, for tall buildings with tops bathed in the
upward stream of light, results inevitably in spoiling the view of the
Earth from the universe, if the viewers come into the beam. The larger 
the beam cone, the larger the cone in the space from which the view is
spoiled...''
\end{quote}

Earlier explanations on architectural and park lighting have been 
published as \emph{Re: A monumental lighting task}
\amper{jenik/letters/public/msg00137.html} and
\emph{Cathedral near Observatory}
\amper{jenik/letters/public/msg00138.html}.


 

\subsection{LPS filtering}

There is a wrong, but widespread opinion that light of several kinds of
HID lamps can  be simply filtered out, to get the starry skies back
easily. At first I  replied that it is not the case even for LPS,  
  \h{amper.ped.muni.cz/jenik/letters/public/msg00156.html}  
 -- then I
searched further and found that, in principle, it is possible for LPS,
being just a bit expensive,   
  \h{amper.ped.muni.cz/jenik/letters/public/msg00158.html}
 (the technology of ``didymium glasses'' had been developed for
 people who treat glass with a flame).

As a fifth measure (0 cd/klm horizontally and above, minimum needed
amounts of light on target areas, as little as possible elsewhere, using 
LPS only) it may become a reasonable help, when paid for by the polluters.
A recommendation stemming out of that is
   \emph{[CFDS] good LPS use should be revived}
   \h{amper.ped.muni.cz/jenik/letters/public/msg00159.html}


\subsection{MLO}

The draft of the Model Outdoor Lighting Ordinance, as submitted to
public  review by the IDA in 2004, appeared to be a bad one for the  of
protection and restoration of healthy and pleasant night  environment.
Our final position is available as
    \emph{MLO2004.1\_j.htm}
    \h{amper.ped.muni.cz/jenik/light/drafts/MLO2004.1_j.htm}

Many discussions preceded this statement, some letters being published:
\bie \raggedright
\item   
 \emph{Fix the MLO (fwd) (and filters at last)}
\h{amper.ped.muni.cz/jenik/letters/public/msg00160.html}

\item
   \emph{[Darksky]Shielding nonsense}
 \h{amper.ped.muni.cz/darksky/2004/000079.html}

\item
   \emph{[magnitude6] Re: USA Model Lighting Code (fwd)}
\h{amper.ped.muni.cz/jenik/letters/public/msg00161.html}

\item
   \emph{MLO V.2004.1, position of Italian orgs.}
   \h{amper.ped.muni.cz/jenik/letters/public/msg00163.html}
 
\item
   \emph{[fixthemlo] Amounts of light}
   \h{amper.ped.muni.cz/jenik/letters/public/msg00171.html}
\ei


\subsection{Luminaire photometry tool}

I have supplemented my command-line programme ies2tab by a possibility 
to convert luminaire photometric data from 
ies to eulumdat format (as far as I know, this became the 
only standalone and free convertor). The programme and scripts easing 
its use for batch processing of thousand of files is within 
\amper{light/ies2}. The original purpose of the programme was getting 
cutoff categories from photometry files and computing the (obsolete)
increase of skyglow due to direct emissions over horizontal directions.

\subsection{Monitoring night sky by PV plants}

An idea coming from Thomas Posch has been published: any photovoltaic 
plant can become a sensitive device for measuring night sky brightness, 
when it ceases to produce power after sunset,
see \amper{jenik/letters/radiometry/msg00014.html}. (A student of 
Masaryk University in Brno, Tom� 
Mil�� began to work on the issue just at the end of 2005.)


\subsection{Legislation}

Our legislation efforts produced at least one useful output, a 
short English text containing the minimum needed set of rules to be 
implemented together. We have attempted (in vain) to put it on agenda of the 
European IDA Symposium in Paris, see a letter from July 1,
   \emph{[Darksky]Endorsing an EU legislation}
     \h{amper.ped.muni.cz/darksky/2004/000065.html}.
An updated version has been made then in 
November (that version is on our web now). 

Recommendations for our draft came from just a couple of experts  (Fabio
Falchi, Pierantonio Cinzano, Cliff Haas -- I think he insisted we should
not say ``downward'', giving a wrong impression  that the law demands
``steep down'', we obeyed it later).

\section{2005}

\subsection{Legislation}

The former deputy Stanislav Fischer returned to the House of 
Representatives -- that one, who proposed the inclusion of protection 
of the air from outdoor lighting into the bill of the Czech Clean Air 
Act, and who achieved that first small step in 2001/2002 
(became an IDA member afterwards). 

The bill for an amendment of the Act came to the House early 2005, 
leaving it unchanged (i.e., minimised) as regards night atmosphere
protection. We have agreed that he will submit a proposal for its
change. He did so, with a  text not much differing from the English
version from November 2004.

No campaigning at all took place, we just wrote to a couple of 
Representatives, and Fischer spoke shortly at the plenary session. 
Surprisingly, a non-negligible amount of MPs (almost one third of  those
present) supported his proposal, across the parties. The Minister of
Environment took a neutral position (a step forward against 2003).

For the Minister and those Reps who cared, we had two new arguments, 
not available in 2003: the huge report on night
environment, prepared  for the ministry in 2004,
\h{amper.ped.muni.cz/noc/}, and a translation of the 2004 amendment 
of the 2000 Lombardy law -- together with a synthetic current 
version of Lombardy legislation it is at 
\h{amper.ped.muni.cz/light/zakon_oo/2005/lombardie/}. 

We are afraid that the Czech translation is the only one in the world,
what is a bit a shame -- the Lombardy legislation, together
with the  subsequent legislation of further provinces (five other before
the end  of 2005, more than 20 million inhabitants), has survived the 
test of the time, and remains to be the best template for all the world.
(Let's remark that a notable new feature of the laws accepted in 2005 is
the correct 
\emph{definition} of light pollution: \emph{alteration of the natural
levels of light}. Outdoor lighting \emph{is} polluting, what we try to
achieve, is either minimising its most adverse consequences, or avoiding
it  altogether when possible.)

In August, we prepared a Czech bill with simpler wording, implementing 
some changes in the Lombardy legislation. Together 
with that which has been submitted in spring, it is within
  \h{amper.ped.muni.cz/light/zakon_oo/2005/}
 This bill has not been submitted yet, the House being 
overloaded and the MPs being busy with the future elections. 

\enlargethispage{5mm} 

Its English analogy (with an added exemption for beamers with sources 
fainter than 1500 lm and lasers below 5 mW) is available within
  \h{amper.ped.muni.cz/light/law/Jan06/},
open to the international discussion. We shall submit the 
Czech version of this bill this year.

\subsection{National Park at Night research}

Already at the end of 2004, people from the oldest and largest National
Park in the Czech Republic, Giant Mountains (Czech: Krkono�e, German:
Riesengebirge; \h{www.krnap.cz/en/}), responsible for  nature
protection there, asked us if we could investigate the night aspect of
\emph{landscape character} there and its changes due to artificial
lighting in general and ski slope lighting in particular. 

We put together a team consisting of two architects (Jitka Brychtov�,
Josef Krause), experienced experts in landscape  character assessments
(just daytime ones, before this project) and me. During several stays 
in the Park in 2004/2005 winter, we have visited and documented many 
localities, views and circumstances. A comprehensive final report in
Czech  has been published in summer 2005, see \amper{noc/krnap}.

Visual evaluation and imaging digital photometry were our main tools. 
Imaging photometry was supplemented occasionally by luxmeter 
measurements on the spot, to know some values instantly and to have 
some check values with which the imaging photometry could be compared 
later. The main instrument was a compact digital camera Nikon Coolpix 
990, equipped with a fish-eye convertor FC E8 when needed. This set had 
been calibrated photometrically and the needed software developed in 
the same time (my programme raw2lum and an adaptation of a standard 
\www{dcraw}{http://www.cybercom.net/~dcoffin/dcraw/} software). The 
software is free, available from \amper{light/luminance}. (The last
stage, compensation for  vignetting -- light loss -- far from the centre
of image, has been solved too already, but is yet to be implemented to the 
report results -- ignoring it means, that the amounts of light are 
partly a bit larger than the report says).

One result had to be expected: clear night moonless sky in the National
Park is at least twice more luminous than a natural sky. It concerns 
even the ridges of the highest Czech mountains. Milky Way is visible, 
but not at all fascinating, due to the common sky luminance of 
0.5\cdpms{}. Strong illumination of just two ski slopes (Hromovka and 
Javor), when operating, causes the clear sky luminance to increase to
about  twice higher levels, to one millicandela per square metre --  or
``one millinit'' as it can be called as well -- or even to several 
millinits, in direction toward these major sources of pollution. These 
are already city-like values (like those measured in Brno, 
second-largest in Czechia, after Prague), rather shocking when we consider 
they are encountered in a mountain National Park.

Another result was even more serious. Relative level of pollution of the
night environment increases by orders of magnitude, when there is a 
cloud layer over the mountains. We summarised the results in the 
following table, using a more common quantity, namely the illuminance 
of the ground, concerning winter conditions with a snow-covered 
landscape:

\begin{center}
\noindent
\begin{tabular}{|p{5cm}|c|c|c|c|}
\hline
\multicolumn{5}{|c|}{Illuminance of the Giant Mountains landscape / 1 mlx} 
 \\\hline\hline
Environment & \multicolumn{2}{|c|}{Full Moon}  
             & \multicolumn{2}{|c|}{Moonless night sky} \\\hline
  & cloudless  & overcast & cloudless & overcast \\\hline\hline
Natural & 
 100  & 1 to 10 & 1 & 0.01 to 0.1 \\\hline
With artificial lighting, without ski slope lighting & 
     &  &  3 to 100 & 10 to 100 \\\hline
Including ski slope lighting & 
     &  &  6 to 300 & 20 to 300 \\\hline
\end{tabular}
\end{center}

\noindent
In another words, the \emph{night light levels at this National Park 
are commonly 100\mtimes{} to 10000\mtimes{}  higher than the 
(desirable, for protected nature) natural ones}, in case of overcast
weather.  This is no minor pollution! All nights, when light is
recycled  between snow and thick clouds, there is like if a constant
waxing Moon in the Park (just the shadows are missing), instead of a
pitch-black night, proper to the Nature. 

The very high light levels are not the only problem. \emph{The landscape 
character changes tremendously from day to night, as the lights 
themselves become dominant}. Every minor daytime-visible detail (as the
colour of roofs,  shape of windows) is considered thoroughly during any 
building permission procedure, but the night appearance of built 
environment has been completely neglected. Strong visible lamps over 
the ski slopes are far more disturbing than the lit snow itself. 

This was not unexpected, but two findings were. In many cases, the 
luminous (strongly illuminated and a bit dispersing) air in the valleys
prevents the landscape behind it to be visible at night, almost zeroing
its contrasts. And some cases, illuminated mountains slopes reach the 
luminance of the sky behind them, and the ridge outline ceases to be
discernible. \emph{When the illumination the ski slope Javor\footnote{in 
one of the two main tourist centres in the Park, Pec pod Sn�kou 
(Petzer)}  is switched on, the second largest Czech mountain,
``Studni�n� hora'' (Brunnberg)  disappears...} Just the highest one
in Czechia, Sn�ka (Schneekoppe) remains slightly visible, being farther 
from the lights and partly screened by the forest. Even David
Copperfield could not achieve more... 

Quite probably, our research was the first one concerning many aspects 
of night environment in any National Park worldwide... The other ones, 
like those in the US, concerned mostly just clear sky luminance. 


\subsection{Tolerable ski slope lighting}

Our report investigated also a possibility how ski slopes could be 
illuminated with minimised consequences for the environment. Apart 
from an evident need to emit almost no light outside the target strip of the 
slope (full shielding alone is not sufficient here; no lights should be 
visible to people standing even at the bottom of the valley), the 
total amount of emitted light is to be small. This necessity is much 
more stringent for white snow than for a asphalt road, because of 
albedo and because of the usual large width of ski slopes.

Our recommendation, which ensures some compatibility with nature 
protection, and enables sustainable ski lighting in this Park, is using 
no more than 0.5~lx, and keeping each illuminated area below 5 hectars. 
The 25 klm emissions needed for the task would not affect areas which 
are farther then 5 km from the slope (and where the slope is not 
directly visible) too much, the increase of light levels would be 
equivalent of illumination by Venus at most. In this way, a slope  which
is more than 5 km away from any First Zone of the Park (First  Zones are
areas, where anthropogenic influence is to be excluded), does  not
endanger it by its illumination alone. A limited amount of  such
illuminated slopes can exist even in the future, provided that another 
illumination (streets, hotels) will be brought to minimum in extent and
in intensity.

Half-a-lux illumination, when properly directed, is sufficient for
skiing in  the same time. This knowledge is based on the experience with
skiing by the full moon (quarter-a-lux at most), on the (much
appreciated) letter by Nancy Clanton (see
\amper{jenik/letters/ski}),  on the theoretical considerations about
visual performance at different scene luminances, and on the minimum 
spot (not average) luminance levels recommended for roads. And, 
moreover, we found a part of one ski slope, which is not avoided by 
skiers, and which has some 0.4~lx illuminance (even if visibility is 
far from being ideal there, due to a glare from a lamp lower on the slope). 

\subsection{SQM issues}

We have solved the task of measuring luminance of all sky  using a
fish-eye camera. However, costly  equipment (one thousand USD at least)
and subsequent computer  processing is needed. In 2005, an new
possibility emerged: a simple  and cheap measuring instrument (like if
an extremely sensitive  luxmeter) has  been developed, called Sky
Quality Meter, see \h{unihedron.com} (Quantity would me a more
descriptive noun, as the reproducibility of measurements is better than
ten per  cent, or 0.1 mag). To the emerging discussion, I have written 
several series of contributions. 

The first one had been on the correct 
transformation of readings to expressing luminances in common units 
-- \cdpms{} -- and on the possibility to call them by the non-SI name 
\emph{nits} (fractional units, as millinits, are even more useful). 
This line started as
\emph{Night Sky Quality Meter},
\amper{jenik/letters/radiometry/msg00009.html} and continues with 
further four items in the archive, 
\wwwt{calling \cdpms{} ``nit'' when needed}
{http://amper.ped.muni.cz/jenik/letters/radiometry/msg00010.html},
\wwwt{Re: calling \cdpms{} ``nit'' when needed}
{http://amper.ped.muni.cz/jenik/letters/radiometry/msg00011.html},
\wwwt{Conversion from ``mg/arcsec\^2'' to \cdpms}
{http://amper.ped.muni.cz/jenik/letters/radiometry/msg00013.html},
\wwwt{Re: Conversion from ``mg/arcsec\^2'' to \cdpms}
{http://amper.ped.muni.cz/jenik/letters/radiometry/msg00012.html}.
          
 Further series stressed the necessity to know ``zenith
extinction'' and offered the  ways to measure it with SQM or estimate visually: 
\amper{jenik/letters/public/msg00188.html}, 
\wwwt{191.html}{http://amper.ped.muni.cz/jenik/letters/public/msg00191.html}
\wwwt{192.html}{http://amper.ped.muni.cz/jenik/letters/public/msg00192.html}
\wwwt{193.html}{http://amper.ped.muni.cz/jenik/letters/public/msg00193.html}

In autumn, I evaluated several types of luminance -- zenith distance
dependencies, from fish-eye images taken in Brno and elsewhere, 
including one remote, just little polluted location. There had been a 
slight problem with existing vignetting of the images (underestimating 
luminance far from zenith), this has been 
corrected later (and implemented into 
\www{raw2lum}{http://amper.ped.muni.cz/light/luminance}). 
The resulting data are within 
\amper{light/luminance/radial}, the very image comparing different 
sites and giving readings assumed for the SQM tested by Pierantonio 
Cinzano is reproduced here:

\noindent\hspace*{-2mm}
\parbox[c]{0.72\columnwidth}{\ing{all_log}}
\parbox[c]{0.27\columnwidth}
{(Early 2006, a contribution
\emph{uses of SQM and how to re-calibrate}
\amper{jenik/letters/radiometry/msg00015.html}
 opened a thread on the angular sensitivity. 
It appears that the instruments differ not negligibly. 
Fortunately, there is an easy possibility to calibrate them for 
narrow-cone or even point-source measurements.)
}

\subsection{Skyglow from the lit ground}

An old argument of polluters about shielding is that  strict
requirements are obsolete -- their ``researchers'' claim most of skyglow
is due to the lit ground, not due to nowadays ``excellent'' luminaires.

We proposed that even if the  question is
solved long ago by computation (over 0.5 \cdklm{} horizontally and 
above becomes too much), for those who need to see to believe, there is a 
possibility to measure the influence of the ground directly, comparing 
snow-covered and snowless conditions. The idea and some evidence is 
available within
\emph{exact answer on shielding and skyglow}
\amper{jenik/letters/public/msg00130.html} and subsequent
\wwwt{131.html}{http://amper.ped.muni.cz/jenik/letters/public/msg00131.html}
and
\wwwt{174.html}{http://amper.ped.muni.cz/jenik/letters/public/msg00174.html}.


\subsection{Education}

Several English-written contributions concern amounts of light and 
shielding. Some of the included info may have been published for the 
first time, but I would not call it research.

One of them concerns
\emph{Traffic Sign Board and Lighting}
\amper{jenik/letters/public/msg00197.html}.

The other two try to summarise the current knowledge of the links 
between outdoor lighting and cancer,
\emph{Re: Light at Night and Cancer}
\amper{jenik/letters/public/msg00194.html} and a more recent
\emph{Re: Light at night-cancer risk in humans verified}
\amper{jenik/letters/public/msg00204.html}.


In 2005, there appeared new publications which  should help to wipe out
the most damaging myth about lighting. We  therefore continued to
promote  the knowledge of real science on crime-light relation (this
time by Paul Marchant), making available the following commentary: 
\amper{jenik/letters/public/msg00181.html}


Reminding people that the theory of skyglow exists (and says that full 
shielding is the most important single measure), seems to be a 
never-ending task. I wrote 
\emph{Three reasons why full shielding is indispensable}
 -- see ``why\_fs'' within
\amper{light/shielding} directory -- and continued with three other 
letters \emph{Re: fco and uplight}
\amper{jenik/letters/public/msg00209.html}, 
\wwwt{210.html}
{http://amper.ped.muni.cz/jenik/letters/public/msg00210.html}
and \wwwt{skyglow from various uplights (211.html)}
{http://amper.ped.muni.cz/jenik/letters/public/msg00211.html}.
The idea is, in short: \emph{light emitted almost horizontally is much more 
harmful} than light dispersed from the terrain. A simple sum of these 
two light fluxes (``amount of uplight'') is no quantity, from which the 
clear sky luminance (skyglow) could be computed (if direct emissions 
are not zero).



\subsubsection{In Czech}

A nice project began late 2005: publishing night photos with 
commentaries within an electronic astronomy newsletter, \h{ian.cz}.
Gradually, more people send in images and comments. We assume to send 
most alarming photos and findings to the corresponding municipalities.


\end{document}

pineal gland, epiphysis, epif�za, �i�inka, corpus pineale
pituitary gland, hypophysis, hypof�za

��k ��kal, �e to byla Bermanova p�edn�ka, a �e to je cirtopic.

Computation of lighting-relevant values
        URL: http://amper.ped.muni.cz/jenik/astro/
