Re: Invitation to Speak in Lebanon

[Jan Hollan <jhollan@amper....muni.cz>]

Dear Jean el Hakim,

these are some themes of lectures I could gladly give. I'd rather leave
the choice upon you -- just then I'd elaborate longer abstracts. For the
workshop, I'd be much in favour of the single topic given below. I can
write a shorter abstract for it, if needed.

with best regards,
 jenik hollan


Possible lecture topics:

Why we don't see the starry heavens any more? Mechanisms of man-made
contribution to sky luminance, glare as an even greater hindrance.

Necessary and sufficient measures to protect the night environment:
technical and legislative ones.

Cultural, health and wildlife impacts of degraded darkness. What
amounts of light do people really need? What amounts are sustainable?

Terrestrial night photometry -- modern approach and results.



Workshop proposal:

                      Photometry of the night

They are several topics I can offer as a useful workshop for those, who
are interested in protection and restoration of natural night
environment. But there is one I have top-level experience with:
        \textbf{photometry of the night environment}.
 I believe I can educate,  within a day, any interested people to become
experts at this field. At least relative experts, in the sense: ``Among
the blind the one-eyed is king'' -- the rest is upon further practice at
home.

In any discussions about sky luminance, glare, and generally about light
levels at night, the question on quantitative measures arises. What's
the amount of unwanted, man-made light, both absolutely and relatively
to natural values? Is it low (units of per cent), appreciable (about 100 per
cent), overwhelming (orders of magnitude above the natural amounts)?
A mere guess is nice and may be enough for those who agree with you,
but your opponents will laugh at it. Give them hard numbers and they
won't any more.

Natural amounts of light at night are mostly enough for human vision,
which is wonderfully sensitive, but are too low to be measured with old
conventional instruments. This may be one of the reasons for the common
strong illumination -- let's have so much light than any luxmeter can
measure it, i.e. several lux and more. Below one lux, there is like if
no light at all...

But natural light levels at moonless night are one millilux at most,
and at least ten times lower under overcast sky, even in an open
landscape. Human vision works well even in these circumstances, but
conventional light-metering instruments don't.

Fortunately, in the past decade, new instruments became common, being
able to integrate light for a prolonged period: CCD digital  cameras.
Astronomers use them since long for photometry, unfortunately  they
neglect to evaluate sky luminances (luminance: how much light comes from
some limited piece of sky) as another important product. And of course,
they don't make any measurements in overcast conditions.  Even in those
rare cases that sky luminances are reported, they concern just
tiny pieces of sky (imaged by a telescope), not the whole sky with its
variable luminance.

Dedicated scientific CCD cameras are a possible tool to image the whole
sky (or alternatively, road, facade, settlement from a nearby hill), but
they are expensive and cannot work without further components
(objective, filter wheel, computer). For faint star photometry, there
is no replacement for them, but for terrestrial photometry, there is
one: common digital cameras with uncooled CCD or CMOS chips.
Those ones, which are becoming to be as widespread as refrigerators,
washing machines, computers or phones.

I have developed a software, which enables to do good photometry with
any
   \textbf{digital cameras which offer storing images as ``raw''}.
 There are hundreds of such products already, and in near future, most
cameras (if not all) will offer such a mode. I have been using three of
them (Fuji S5000, Nikon 990, Canon D60), and I have evaluated many
hundreds of night scenes (there is unfortunately no good English gate to
that, just a neglected http://amper.ped.muni.cz/light/luminance/).

If you have or can borrow such a camera (ideally, capable of making
exposures up to one minute, and still better, equipped with a fish-eye
lens), I offer you to convert it into a scientific photometric
instrument during the workshop. Further on, you will be able measure
any luminances with it. You will be able to verify  compliance of
pavement luminances with technical standards, compute  veiling
luminances caused by glare from distant lamps, measure the  amounts of
light at your favourite observing place. You will be  able to serve as a
regional expert for low-light measurement, probably the only one in your
region or country.

Of course, evaluating images from cameras takes some time, and in many
cases it is interesting to be able to say some values immediately.
There is such an instrument now, for USD 120: the
   \textbf{Sky Quality Meter (SQM)}, from unihedron.com.
  The workshop will teach you how to use it for most diverse tasks. SQM
works even for non-scientists -- the only need is to learn the world of
photometry quantities, including the queer astronomy-specific ones. We
shall overcome this barrier during the workshop.

If you have a luxmeter, take it with you. We will calibrate it using
another ones, and we will learn how to calibrate cameras and SQMs using
luxmeters. We will also learn how to calibrate  luxmeters using Moon and
Sun, and how to measure atmospheric transparency using luxmeters.

If you are doing astronomical photometry, we will discuss how  to get
sky luminance data from your measurements as a by-product. This  is not
vital for future measurements (ordinary digital cameras and SQM are
mostly better instruments), but may be useful for being able to get
data from past years. Does your sky deteriorate or does it get better?

Finally, we will discuss jpeg photometry -- a more laborious, less
sensitive, but a possible and proven method. Again, even old images may
be processed to get luminance values. They may become a treasure, like
old glass plates for variable star research.