The Call of the Open Sidewalk

Much of the earlier habits of Earthly society have been given up in the interest of that same economy and efficiency: space, privacy, even much of free will. They are the products of civilization, however, and not more than ten thousand years old.

The adjustment of sleep to night, however, is as old as man: a million years. The habit is not easy to give up. Although the evening is unseen, apartment lights dim as the hours of darkness pass and the City's pulse sinks. Though no one can tell noon from midnight by any cosmic phenomenon along the enclosed avenues of the City, mankind follows the mute partitionings of the hour hand.

The expressways empty, the noise of life sinks, the moving mob along the colossal alleys melts away; New York City lies in Earth's unnoticed shadow, and its population sleeps.

The Caves of Steel, Isaac Asimov, 1953

OK, here we are living in the future. Others have written at length about the absence of flying cars but what about wildly artificial environments? Space habitats? Underground cities? Huge isolated skyscrapers? Floating cities? Cities at the bottom of the ocean? Any sort of archology at all? The sort of places that the geeky set can have adventures in (or at least be respected for their ability to function in high tech environments). A science fiction cliche. The only reason Asimov bothered to describe his Cities in any detail was because he wanted to do a detective mystery there. We all knew what he meant.

Classic science fiction about such places can now be considered to be incomplete in light of our recent knowledge about circadian light. The required means of regulating circadian light and the associated rules would change a lot of narrative.

The interesting real life questions are:

Does the circadian light idea allow us to create entirely artificial environments?

and (less important)

Does the circadian light idea allow us to improve the sort of indoor environments we face today?

posted at: 11:48 | path: /clight | permanent link to this entry

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 | permanent link to this entry