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[DSLF] Digest Number 1732

There are 3 messages in this issue.

Topics in this digest:

      1. Re: Light at Night and Cancer
           From: Jan Hollan <jhollan@amper....muni.cz>
      2. Re: Light at Night and Cancer
           From: "Terry McGowan" <lighting@ieee...>
      3. Re: Light at Night and Cancer
           From: ctstarwchr@aol...


Message: 1         
   Date: Fri, 12 Aug 2005 00:08:04 +0200 (CEST)
   From: Jan Hollan <jhollan@amper....muni.cz>
Subject: Re: Light at Night and Cancer

> Light levels in the range of full moon illuminance
> have been proven to trigger this negative effect on suppression
> of melatonin in humans,


this is true, but applies without any question just for light at some
460 nm, where photopic sensitivity is low, or at even shorter wavelengths
(with photopic sensitivity still lower and the non-imaging visual system
still very sensitive).

For any common light sources (artificial, Moon, sky) the problematic
illuminations _of the eyes_ start at several lux perhaps. This translates
to the problematic illumination of the terrain (assuming no glare) of
perhaps twenty lux (assuming its albedo 0.15).

In another words, outdoor lighting is mostly not so strong that it would
affect melatonin production -- esp. sodium lighting with little shortwave
proportion. The possible/probable fatal influence is due almost solely to
indoor lighting.

Sleep disruption, however, is starting at 0.1 lx falling onto windows
(Moon near full), and simply because of that ever known and well known
fact we can say that light begins to be toxic at night starting at
centilux level (of illuminance of the eyes). Melatonin-reducing toxicity
starts at orders of magnitude higher values (and closed eyelids shift
the threshold to ten times higher level again, filtering the blue and
green component a lot).

My suspicion is, however, that during dark weeks with no direct sunlight
and heavy clouds (or for indoor-staying people) the sensitivity of
circadian-synchronising visual system to faint light might grow, so the
safe levels preventing reduction of melatonin production at night may be
ten times lower in such circumstances.  We cannot exclude that outdoor
lighting is strong enough in winter to be a metabolic problem too...

Treating light at night as a toxic pollutant means a profound change of
attitude toward lighting. This change is necessary for achieving
fundamental improvement of current indoor lighting as well as that of
outdoor one.

Light as a toxin will be regarded very differently from light as an
unconditional blessing.

Still, people should know there are safe levels of light at night.
Candle at 1 m from the eyes won't reduce melatonin production. A purely
yellow light (showing pure blue objects as dark grey), achievable by
filtering (or by using LPS or special pure yellow linear fluorescent
tubes) won't compromise it even at ten lux eye illuminance. We can have
sufficient no-regret light at night before going to bed. Even TV screen
should be tolerable (even if it would be better to dim its blue pixels).



Message: 2         
   Date: Fri, 12 Aug 2005 09:18:21 -0400
   From: "Terry McGowan" <lighting@ieee...>
Subject: Re: Light at Night and Cancer

The web site http://www.lowbluelights.com  has some additional information 
on this subject and an up-to-date list of research papers.  It's also an 
example of one way a small part of the lighting industry is beginning to use 
the information.

In the interests of full disclosure, one of the researchers, Dr. Richard 
Hansler, is a long-time friend and colleague.  However, I do not have any 
financial or any other business interest in the companies mentioned.

Terry McGowan

----- Original Message ----- 
From: "Greg Crawford" <gc@nelsonbay...>
To: <DarkSky-list@yahoogroups...>
Sent: Wednesday, August 10, 2005 9:01 AM
Subject: RE: [DSLF] Light at Night and Cancer

> I've already discovered an error in my own letter. The pathway appears to 
> be
> through the hypothalamus to the pituitary gland, but that is getting a bit
> technical for a letter to the editor. I would replace the relevant 
> sentence as
> follows:
> "The light triggers specialised retinal ganglion cells in the eye which 
> signal
> the brain to suppress melatonin."
> - Greg
> -----Original Message-----
> From: DarkSky-list@yahoogroups... [mailto:DarkSky-list@yahoogroups...] 
> On
> Behalf Of Greg Crawford
> Sent: Wednesday, 10 August 2005 10:35 PM
> To: DarkSky-list@yahoogroups...
> Subject: [DSLF] Light at Night and Cancer
> I'm about to respond to a letter to the editor in our regional newspaper 
> which
> asked about the causes of cancer. (This followed a feature highlighting a 
> higher
> than normal incidence of cancer in our region.) I would appreciate 
> people's
> responses on my letters accuracy. I have had to keep it brief to match the 
> word
> limit. The letter is below. (I have also sent a copy yo Stephen Pauley.)
> - Greg
> [Name of previous author] (Herald 10/8/2005) asks what the causes of 
> cancer are.
> One factor often overlooked is exposure to light at night. Ongoing 
> research in
> U.S. universities has shown that exposure to light at night leads to 
> suppressed
> production by the body of the hormone melatonin. Melatonin not only 
> enables a
> person to sleep, it is also "oncostatic", meaning it helps stifle the 
> growth of
> cancers. The mechanism by which light at night suppresses melatonin is now
> known. The light triggers specialised retinal ganglion cells in the eye 
> which
> connect to the pituitary gland. Experiments with both laboratory animals 
> and
> human beings clearly demonstrate the mechanism. Furthermore, controlled
> experiments in which laboratory animals are subjected to light at night 
> clearly
> demonstrate an increased incidence of cancer as a result. It is 
> interesting to
> note in this regard that night-shift workers also demonstrate an increased
> incidence of cancers. While daylight naturally suppresses melatonin 
> production,
> continued suppression right throughout the night by artificial lighting 
> presents
> a health hazard. Further information can be obtained from a research task 
> force
> investigating the phenomenon at 
> http://www.darksky.org/wrkgrups/phobiowg.html


Message: 3         
   Date: Fri, 12 Aug 2005 16:15:25 EDT
   From: ctstarwchr@aol...
Subject: Re: Light at Night and Cancer

This is an outstanding resource Terry.  Thank you so much
for presenting it to everyone.  After a quick review I was
very impressed with the amber night light and what they 
said about children being afraid to sleep in the dark.  I 
was too until my parents removed that Felix the Cat clock
hanging on my bedroom wall.  
Imprinting in our DNA likely drives man to exhibit illogical 
behaviors where light and impending doom are concerned. 
The industry as a whole including utilities have capitalized 
on 'fear factors' forever with the 'security light' continuum.
I look forward to reading more of the research papers 
listed on this web site, and it is very encouraging to see 
the lighting industry is starting to take notice to some of 
these health hazard potentials recently discovered in 
scientific research.  Many thanks again for the information!

Clear  skies  and good seeing,
Keep looking up!

Cliff  Haas
Author  Light Pollution Awareness Website    (LiPAW)


In a message dated 8/12/2005 10:59:09 A.M. Eastern Standard Time,  
lighting@ieee... writes:
> The  web site http://www.lowbluelights.com  has some additional
> information on this subject and an up-to-date list of research 
>  papers.  It's also an example of one way a small part of the 
>  lighting industry is beginning to use the information.

[Non-text portions of this message have been removed]


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