Light and Circadian Rhythm Simplified

Boyhood of Lincoln (1868) by Eastman Johnson, The University of Michigan Museum of Art

Circadian Light

Visible light has been linked to improving our health and wellbeing by impacting our circadian rhythms through photoreceptors connected to our biological systems.  While much has been published and many products marketed to assist designers with implementing “human-centric” and “circadian lighting”, there is still a great deal to learn about actually specifying these systems and the value/cost proposition.

In addition to the physiological need our bodies have for certain wavelengths of light, we know there are appropriate times certain colors of light work best for us.  Furthermore, we have psychological expectations of light in our environments.  For example, cooler [whiter, blue rich] light associated with higher color temperatures, and specifically daylight, create an alerting response in our biological systems by suppressing melatonin and allowing us to produce serotonin.  This is the caffeine of the natural world.  Daylight, full of cyan wavelengths at 460 nanometers, is what wakes us up in the morning.  This is good if you are going to the office or school.   It might not be good if you are coming home from the late shift like a healthcare or factory worker.  We’ll come back to this topic in another chapter.

But the natural world knows we can’t stay awake 24/7 and while a good book might help put us to sleep, it isn’t the reading alone that makes us drowsy.  As the sun crosses the sky to meet the western horizon the atmosphere absorbs shorter, blue wavelengths and the sunset glows with longer, warmer wavelengths of light.  It is the reduction in blue-rich light, along with lower light levels, that signals our body to stop producing serotonin and to start producing melatonin to make us want to go to sleep.

For the human visual system, daylight is a perfect source that provides us with a blend of wavelengths balanced across the visible spectrum from 400 nanometers to around 730 nanometers.  Below 400 nanometers we have ultraviolet and above 730 nanometers we have infra-red in the non-visible portion of electromagnetic energy.  Ultraviolet is the reason we need to wear sunscreen and infra-red is how our French fries stay warm.

Light and The Social Fabric

In an agrarian society, people rose and slept on a daylight cycle.  Light at night was provided by firelight, torches, or candles that produced a warm color of light.  Oil lamps and other combustible fuels were helpful but were no substitute for daylight to enhance productivity.  Besides, their use often resulted in catastrophic events.  Just ask anyone from Chicago.

As the Industrial Revolution accelerated society’s transition to urban life, the electric lamp allowed for extended hours of work and social interaction without all that messy combustion.  Early incandescent sources replicated firelight allowing humans to continue our natural circadian cycles.  No one was the wiser.  However, the incandescent lamp was plagued with a short useful life.  That burning filament just didn’t last and we were always having to replace it.  Add in the poor efficiency ratio of light to heat, and some creative individual was bound to invent something better.

Along came the fluorescent tube that became a mainstay of the office.  This was an enormous advancement for efficiency.  Fluorescent sources didn’t burn a filament which allowed them to last substantially longer than incandescent sources.  The problem was the color (and the mercury), but let’s just stick to the color for now.  Fluorescent tubes used an electrical arc to excite phosphors on the inside of the tube to produce visible light.   Phosphors come in different colors like red, green, and blue which happen to be the primary colors of light.   This sounds good, right?

Sort of.  Three major social impacts resulted from the widespread adoption of fluorescent lighting in the built environment. And, if you are too young to remember how bad it could be check out this clip on YouTube.  Joe versus The Volcano

  1. Red phosphors were more expensive than blue and green so why use them if we don’t have to? If anyone remembers we had two basic colors of fluorescent tubes.  Cool white and warm white.  The cool white lacked enough red phosphor and produced a greenish color of white light that wasn’t all that pleasant.  Over the course of the day you just adjusted to the color.   Warm white emitted a somewhat pinkish color with the addition of the red phosphor but the color distortion didn’t make it very popular either.
  2. Fluorescent tubes needed an electrical device, or ballast, to keep the arc going at a particular voltage. Too much voltage and the arc wouldn’t last; too little voltage wouldn’t keep the arc going at all.   Early ballasts operated at low frequencies causing the arc to flicker which many people could not only see but the flicker caused headaches and other health-related issues.  Even with improvements like full-spectrum fluorescents with improved color and high-frequency ballasts (to reduce the flicker), the color and intensity of the lighting continued to impact our circadian rhythm.
  3. The use of clean, efficient fluorescent lighting allowed office workers to work after dark and factories to operate second and third shifts resulting in a significant socio-economic impact on our health. Now instead of warmer, lower levels of light in the evening, we were subjected to cooler, higher levels of light longer than ever before.

What happened next was the beginning of a health crisis that was not discovered for decades.  Couple that with the rise in handheld technology, the impact worsens.  Working late under bright lights at the office we delay the normal sleep-wake cycle with too much blue-white light on a daily basis.  The production of melatonin is delayed causing us to have trouble falling or staying asleep.  Blue-rich phone screens, tablets, and computers mean there is no real break from alerting light entering our eyes.

Looking Forward

What is the solution?  The change in technology to LEDs has not changed the intrinsic biological impact of light.  There is no one quick fix, but several actions taken together will get us back on the road to a well-balanced life.  First, we have to prioritize health and wellbeing as a means for better productivity.  This starts by looking at our built environment and the importance of well-designed lighting systems.  The luminaire [lighting fixture] should not be separated from the lighting controls; both are symbiotic components in a well-coordinated system.  They need to work holistically to produce the intended objective.   The entire lighting system is as important to our health as exercise and good nutrition.