Re: Light at Night and Cancer

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

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

Cliff,

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).

jenik