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20 lx white compromises circadian rhythm
Dear Nick Kelso,
I've just noticed the "light center's" intiative.
As somebody who observes the topic of Light at Night since many years, I
am afraid that the illuminances of 20 lx by cool white light are toxic to
human health at night, diminishing or even preventing melatonin
production. Hopefully, African people without electricity have that
production still almost 11 h long, unlike any European people. This is a
blessing for health.
Using filtered warm white LEDs (I do so at home, using yellow foil which
can be peeled off for a moment, if necessary) or amber LEDs (these are my
choice, we use mostly these), supplemented eventually with some green and
perhaps one dim blue diode, would be far more proper.
And moreover, 6 lx at most - entirely enough even for reading small print
with adequate accommodation (i.e., 4 D glasses for presbyopic people over
47), not to speak about soccer. This is twice the amount available at the
start of civil night at open space, when outdoor lighting is
conventionally switched on. 3 lx would be more appropriate, being still
ten times stronger than the strongest possible moonlight.
Further, as the image at
http://www.philipsafricaroadshow.com/philips-announces-initiative-to-provide-solar-powered-led-lighting-for-100-small-soccer-pitches-or-light-centres-for-rural-communities-across-africa/
indicates, the employed luminaire has large luminous intensity in an
almost horizontal direction; I guess it is no fully shielded one. But it
should be, to prevent disturbing wide surroundings and glaring into eyes
of approaching people.
Illuminating the place at 3 lx, with very small blue component and 0
cd/klm horizontally and upwards, that might be sustainable. The way you're
doing it now is far from that, IMHO.
Actually, using 20 lx white light might be even dangerous for people going
from such a strongly lit place to nature again. Some people don't adapt
quickly enough.
For some background to my advice as given above, please see a draft
(had to be 4 pages at most)
http://amper.ped.muni.cz/light/drafts/hollan_light4h.pdf
and the links from it.
yours sincerely
Jenik Hollan
PS
below: an example of a photometric evaluation of another LED
luminaire -- I'll gladly do the same for your products
---------- Forwarded message ----------
Date: Tue, 2 Oct 2012 12:08:16 +0200 (CEST)
From: Jan Hollan <jhollan@amper....muni.cz>
To: magnitude6@yahoogroups...
Cc: darksky@amper....muni.cz
Subject: Re: [magnitude6] Re: Batlamp - the ultimate LED streetlight for
protecting the night sky?
I've put the illuminance plots and luminous intensity tables to
http://amper.ped.muni.cz/light/ies2/innolumis/
The ldt file has no data over 90, so no ULR can be computed ;-)
-- see the tables. We can just realistically hope that all number over 90
degrees would be 0.0 cd/klm. Omitting values over 90 degrees in photometric
files is a bad habit. Here it presents no swindle for sure, but for another
luminaires, it could.
We have to ensure 0 cd/klm. ULR is to be 0,00 %, it mostly is with 0 cd/klm.
I've added some text (and an *.ies file) to the above directory and computed
a case for spacing 3, at 5 m height, using my own online php.
It looks nice, see for yourselves. The only problem is with so much light
falling behind the lamps, making them a really good choice just for a
situation of a road in front of the poles and a broad sidewalk behind them.
cheers, jenik
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Jan Hollan, Ph.D.
CzechGlobe - Global Change Research Centre of the Acad. Sci. Czech Rep.
AdMaS - Advanced Materials, Structures and Technologies Centre of the Brno
University of Technology
home:
Lipová 19, 602 00 Brno fix. +420 5 43 23 90 96
mob. +420 606 073 562
volunteer of the Ecological Institute Veronica
Panská 9, 602 00 Brno, Czechia http://www.veronica.cz
e-mail: hollan@ped....cz http://amper.ped.muni.cz/jenik
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