When light pollution is mentioned, it is mostly vague what is meant by it. Attempts to clarify it lead usually just to more confusion and misunderstanding. This caused even exclusion of this kind of pollution from quantitative environmental assessments.
Even those who want to reduce this kind of pollution are often unwilling to admit that any light added artificially to the outdoor environment at night pollutes it, inevitably. The only scientific definition published in peer-reviewed literature up to now is by Cinzano et al from 2000 (slightly reworded to make it clearer): the alteration of light levels in the outdoor environment (from those present naturally) due to man-made sources of light.
Consequent thinking about the ways how this alteration could be expressed or measured leads to full understanding of how the various facets of this “vector” kind of pollution look like. This has been done in http://amper.ped.muni.cz/light/lp_what_is.pdf (or its html version) and will be summarised in the talk.
Human metabolism and awake-sleep patterns have developed under natural variation of light levels. Its amplitude, expressed as illuminance of face, used to be 1:109 (assuming that people were outside in daylight and hidden in shelters at night). Nowadays, it is mere 1:104 for some of us.
Sufficient variation is needed for a proper production of hormone melatonin during all the night. Fortunately, we can afford enough light to read or work at night, without compromising the onset of the nighttime metabolism phase – simply by filtering out the blue third of the light spectrum and keeping the remaining yellow part at modest levels of several lux or tens of lux at most, with a possible exception of a small target area.
Much lower limits are needed during sleep at night, but even these exist and are easy to obey: one centilux of face illuminance appears as harmless.
There is but a Czech text with English abstract available on the subject: http://amper.ped.muni.cz/jenik/domy/svetlo.pdf It will be available in English by the time of the conference.
Any digital camera storing raw data can be used as a luminance (radiance) measuring instrument. The needed calibration steps and the software available for them will be described. For faint light, not all cameras are suitable; the good ones report at least 90 % of dark pixels as having values larger than 0. For a previous lecture see http://amper.ped.muni.cz/light/lectures/06IAU50t_small.pdf and for technical information http://amper.ped.muni.cz/light/luminance
Many Czech sites have been investigated using digital imaging. A selection of interesting images will be discussed, illustrating good and bad examples of outdoor lighting quantitatively.
Hostetin got a honourable mention at the last IDA European meeting. See http://amper.ped.muni.cz/noc/hostetin/comparison.htm for values achieved by the new luminaires donated by Philips Lighting. Further improvement achieved by cheap adaptation of luminaires will presented for the first time.
Years ago, a programme ies2tab has been made to get human readable data from luminaire photometric files, then the relevant luminaire parameters, and finally, in 2007, the illuminance plots. A huge catalogue of such plots is available at http://amper.ped.muni.cz/light/ies2/EasyLight-SaveTheSky/ and its neighbour directories. Online computation is offered at http://amper.ped.muni.cz/light/ies2/online/
With additional scripts, the application sorts thousands of photometric files according to maximum specific luminous intensity about 70 degrees from nadir – these are candidates for maximum possible relative spacing (ratio of distance of neighbouring posts to the height of luminaires).
Some luminaire manufacturers offer antireflection coating of the bottom lens. The technology for that has advanced immensely in recent years. http://amper.ped.muni.cz/light/EuP/antir_bookm.htm are some relevant links, http://amper.ped.muni.cz/light/EuP/FS.htm describes fully shielded luminaires advantages taking into account this new possibility. http://amper.ped.muni.cz/light/EuP/transmis1.25.png gives the transmission curves. The new “invisible” glass will be demonstrated at the conference and compared with older types of glass and plastics.
The Sky Quality Meter has become the most widespread luminance meter for faint light. Optical adaptations of this instrument enable to measure narrower cones, using it as a tool to investigate luminances of any surfaces, see http://amper.ped.muni.cz/jenik/letters/radiometry/msg00021.html. Recalibrating the adapted SQM is easy and will be demonstrated. Using SQM is a way to calibrate even the digital cameras without using a standard luxmetre.
Jenik
PS. Reading the excellent paper by Dr. Clark (A Rationale for The Mandatory Limitation of Outdoor Lighting) is another task I'm honoured to be asked to do. In fact, I could also make any short or long introduction to climate issues, as I'm giving lectures on that since 1990 and have edited the Czech translations of the three recent Summaries for Policymakers as published by the IPCC in the past months – but I assume that some insider will make it in Bled. (The Czech translations and vector figures easy to adapt to another languages are available from http://klima.hvezdarna.cz.)
