Like the food we eat and the air we breathe, the light that enters our eyes
changes the very chemistry of our bodies.
And different kinds of light affect us in different ways.
Take the sun. Its intense, high-energy waves keep us active and alert.
Darkness signals our bodies to produce melatonin, a hormone that helps us sleep.
But we don’t rely on sunlight that much anymore.
And as we change the kinds of light we use, our bodies are changing too.
There are dozens of studies on this. But one recent one out of Penn State showed that people
who used e-readers at night weren’t as alert the next day as those who read paper books
the night before.
And sleep itself -- the very nature of it -- has changed.
Early texts reveal that before the 17th century, in Europe at least, people didn’t sleep
in eight hour blocks.
They’d wake up after four hours, stay awake for a quiet hour or two - then fall back asleep.
And studies suggest that this is our natural rhythm. Deprived of artificial light, we revert
to these old patterns.
Our earliest illuminations didn’t mess with our sleep so much. We used campfires and torches.
Then stone lamps.
Sometimes people would just thread a wick through an oily fish or a bird.
Big cities glowed under gas lamps in the 17- and 1800s.
But the oranges, yellows and reds of those lights have long wavelengths, which don’t interfere
much with melatonin production.
The big change came in the 1900s with electric light.
… from incandescent and neon to LED.
These lights -- like the sun -- can suppress melatonin. So they signal our brains to be
active.
Our segmented nights have disappeared.
Getting less sleep? Everyone knows that’s a bad thing.
But this is about more than that: it’s a loss of a distinct mental state, a sort of…
liminal zone that we used to occupy in the middle of each night.
During this time our brains were flooded with prolactin, the relaxation hormone enjoyed
by breastfeeding mothers and post-coital lovers. It was a time to read quietly, write, smoke,
have sex, or just think.
Today... in our digital, relentlessly productive society, it seems almost magical,
doesn’t it?
A time of day set apart -- not quite asleep, not quite awake -- hovering somewhere between
dreams and wakefulness, darkness and light.