[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

----------------------------------------------------------------------
                             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
----------------------------------------------------------------------