Did you ever watch a moth express a unnatural and disturbing desire to
become one with the filament of a light bulb? I tend to feel sorry for
the moth and, I must confess, a little bit superior. After spending
way too much time reading about circadian light I think that in the
future I will feel a little less superior.
In a previous
post I mentioned something about blue light and circadian
rhythm. It turns out that mammals have an entire separate visual
system devoted to synchronizing circadian rhythm to
the local light/dark cycle. The existence of this system was entirely
unknown until recently. I would like to state at this point that I
think that the people who figured all this out are awesome. All the
important stuff was worked over a period of less than 10 years. It was
definitely a triumph. I suspect that even now it is still pretty
difficult to get funding to study something no one learned about in
school. Imagine what it was like to propose that there was this huge
thing that everyone else had missed in the beginning.
Basically there are slow ambient light sensors in the eye that are
connected directly to a biological oscillator with a period of 24
hours. This oscillator is phase locked to the light/dark cycle and in
turn locks various systems to the light/dark cycle. The system is
most sensitive to light in the range from 450 to 480 nm. Light of this
wavelength is perceived by the daytime visual system as
blue. Here
is a nice summary of what was known in 2003. Check out the figures.
Following this I will freely mix the ideas of myself and others in
infotainment style.
Much of this is still not understood
... least of all by me. Even the reasons for having a circadian rhythm at
all are not clear. The explanations I have seen state something
to the effect that the circadian rhythm is important because it
regulates important stuff. Some arctic animals get rid of of it
entirely in the dark months but start it up when the light returns
(
(Ref)Thanks
Gord). This implies that maintaining a circadian rhythm is
expensive. At the same time it implies that the cost is worth it
somehow.
The thing with these systems created by evolution is that evolution
can't actually design anything. It doesn't matter that no one can
understand it or even that it makes sense. It just has to work. Stuff
like this is why I avoided taking anything like biology in
school. Every path leads down the rabbit hole. I strongly prefer
things that make sense in a simple way. Evolution sucks.
What is understood is that people are directly controlled by
light levels in a very direct way. We just don't know what all the
implications of this are.
"Wait, how many marks do I get for this?"
While reading through related papers I was struck by the apparent
level of dedication shown by the human experimental subjects. These
sort of things are mostly inflicted on students. Students tend to
think that the most outrageous form of physical humour involves drawing
stuff on drunk people. Thus it must of seemed that they were part of
someone else's hilarious practical joke. When pushing back the
frontiers of this particular bit of science you get to:
- Put up with people shining bright lights directly in your face.
- Sit alone in the dark for hours extending to days ... often with a
thermometer in your butt.
- Stare at an illuminated surface ... without moving your eyes
... for up to 6 hours. At least one experiment had a video system to
allow someone to yell at you if you attempted to move your eyes.
- Wear incredibly dorky glasses in public. Funniest when applied to
teenagers
(Ref).
Melatonin
Circadian light significantly reduces the level of a hormone
called
melatonin. The
hormone is reasonably easy to measure and is dramatically effected by
light exposure. Thus people like to use it as an indicator that
circadian light is being detected. Since it is the thing everyone is
measuring people tend to fixate on it when coming up with
theories. Light makes it go away fairly fast (15min) but it can take 3
hours to return in darkness.
Age
Older people are significantly less sensitive to circadian light than
younger people. In an analogous way to the way people loose the
ability to hear short wavelength sounds as they grow older they also
lose the ability to sense shorter wavelengths of light. Circadian light
is at the short wavelength end of the spectrum and gets
attenuated. The first graph
from
this
shows the spectral characteristic of the lens of the eye with respect
to age. Fluorescent lighting has a large spike of energy at
435nm. This would be effective as circadian light. Past the age of 20
this wavelength is strongly attenuated. It might be reasonable to
assume that children and teenagers are much more effected than adults
by fluorescent lighting. I suspect that is part of the reasoning that
led to studies like
this.
Circadian light is good
People living close to the poles tend to live without much natural
light for much of the year. This can lead to various problems. The
most famous of these is seasonal affective disorder (SAD). A common
treatment involves sitting in front of a box full of fluorescent
lights for a while in the early morning. Circadian light is generally
assumed to be involved somehow. One idea is that melatonin prevents
the production of serotonin which in turn prevents the person involved
from feeling good. So... circadian light can make you happy...
In general people like brightly lighted places. I bemoaned that fact
in this post when I was discussing low
level lighting. Those people back in the day were not just wasting
energy with their extravagant light levels. They were possibly
improving the mood and health of the people who worked there. The
present standard for office lighting calls for 500 lux. You need
1000-2000 lux to get a reasonable circadian effect. Typical factories
and warehouses tend to be dimmer than offices.
Circadian light is bad
Bright light in the evening can retard the circadian cycle in
people. The effect can be increased where there is no exposure to
light in the morning. This could mean that the affected person would
stay up later and have trouble getting up for work/school in the
morning. The net effect would be a general lack of sleep.
The question of "How much light is too much?" is a bit
complicated. Fluorescent lighting at 2000 lux would certainly have an
effect after sundown. The traditional well shaded 60W incandescent
sitting on an end table in a living room is not likely to make much
difference. TVs and computer monitors might have an effect. For
example, my monitor is rated at 300 nit. That is equivalent to 940
lux. That sounds a bit bright but the monitor only occupies maybe
1/4 of my visual field. That is important because the circadian light
sensors are well scattered in the retina. We can't stop here because
when people say that 2000 lux is significant they mean
illumination. Only the light that is reflected from the surroundings
ends up on retinas. The rule of thumb seems to be a factor of
5. So we are down by 4 and up by 5 which may mean an equivalent of
1200 lux of fluorescent lighting. That still sounds a bit high.
There are of course programs to play with for people that want to
experiment with reducing evening light exposure caused by their
monitors. A program
like Redshift that adjusts to
a warmer colour temperature at night might help. The idea is that
warmer means less blue light from the screen. For those trapped in the
MS Windows
environment F.Lux does
the same sort of thing. The less technical solution for those
concerned is just to turn down the brightness of the monitor/TV at
night.
The "C" word
This section could be subtitled "Circadian light is
real
bad". I get the impression that there is a relatively large amount of
money available for cancer related studies. When you look harder you
find more stuff. It is then no surprise that there is a theory linking
circadian light to cancer.
A study showed that women that work night shifts tend to have more
breast cancer. Also, people in developed countries tend to have more
cancer than people in less developed countries (citation needed). What
do night shift workers and people in more developed countries have more
of? One thing is artificial light.
The growth of at least some cancers has been shown to be reduced by
the hormone melatonin. More light means less melatonin so we end up
with more cancer.
I am sceptical myself. As mentioned earlier, most workplace
artificial light environments do not count that highly as circadian
light. Since shift workers tend to create a dark environment to sleep
in (and close their eyes) the extra melatonin suppression could only
be what counts as the evening hours for the particular person. That
would be only something like 3 hours down from the normal 8 or 9 hours
of high melatonin levels. Significant, but most of it is still there.
If artificial light does in fact cause cancer this would be one of the
most significant unintended effects related to a technology in human
history.
Nightlights make no difference
This all started with a night night that had bluish/white
LED's.
This
well done experiment shows that a lower limit of 0.01 W/m2 for
circadian effect would be reasonable. My calculations were quite
rough. I assumed that someone managed to stimulate their entire visual
field for 15 min (the time used in the study) with the light from my
night light. I also assumed that all the light energy was moved to the
circadian wavelengths. Since that light energy ended up being less
than 0.01 W/m2 I think it is safe to say that my night light was not
going to disrupt anyone's circadian stuff. It would be hard to think
of a reasonable night light that would. From time to time the news
media does a popular science article on the circadian light
thing. Sometimes this gets livened up to "Is your childs night light
harmful? Find out at 9!". For extra excitement they throw in the "C"
word. So to that I say, no, it isn't. If it bothers anyone they can
just stick the thing behind a dresser. "For extra safety!".
There is a lot of bogosity here
One of the nice things about writing articles about things wildly
outside my expertise is that I can say things that might be a lot more
insulting coming from someone more knowledgeable. Anyone with a light
meter, access to a freezer, and a test lab can do a study involving
circadian light. The catch is that a lot of this stuff is wildly
unknown and it is hard to know what needs to be controlled. That does
not mean that I think that the simple studies are worthless. It is
just that they should not be used to back up things like news
articles, wikipedia entries, and products.
Let's play along at home...
It might be fun do some some wild speculation of our own. For extra
fun let's be slightly political.
Daylight savings time causes unhappy/tired people!
This applies to the situation where just as the day becomes long
enough to see light in the morning daylight savings time kicks in
plunging morning commuters back into darkness. Since the lack of
morning light is bad then daylight savings time is bad for a few
months in the spring. In the height of summer daylight savings time
results in a lot more light late in the evening. Also bad.
The ban on incandescent bulbs will cause tired/unhappy people!
Canada is planing to ban light sources that use hot
filaments. Incandescent bulbs create relatively little blue
(circadian) light. Compact fluoresents could be expected to have more
of a disruptive effect in the evening. Children/teens would be more
affected by this. The "Find out at 9!" article writes itself at this point. If
you dim an incandescent it produces virtually no circadian light. This
option does not exist with compact fluorescents.
With great knowledge comes great responsibility
People are already trying to use this new found knowledge to abuse the
working class. Yes, 3% extra productivity justifies any
means. Employers have been fiddling with lighting for years. The
problem is that now lighting at work is known to have an effect on
life outside of work. I would not be surprised to see circadian light
issues show up in future employment contracts. Even if an employee
accepts a particular situation is it then ethical to fiddle with stuff
that might conceivably have an effect on things like reproduction
(
Ref1,
Ref2)?
What should we do?
I don't know about other people. Poorly understood? Potentially
powerful and/or dangerous? Great! Let's try to hack it! More later...
posted at: 16:40 |
path: /clight |
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