Let There Be Light–Or Not!

Daytime is bright. The night is supposed to be dark. We work during the day, and we should sleep at night. These are fairly simple concepts around which the human body was designed. Our hormones and our health depend on these principles.

Let there be sunshine

We need the sun and its light, all 32,000 to 100,000 lux of it (on a bright, sunny day). Even on an overcast day, the sun grants us 10,000 lux. Without sunshine, we would be miserable, or maybe not exist at all. We have all heard of Seasonal Affective Disorder (SAD), a type of depression suspected to result from not enough hours of sunlight.

So what is a lux? A lumen?

A lumen is, broadly speaking, the “quantity” of visible light that a source emits. A one watt lamp radiates approximately 683 lumens.

A lux is a measure of the intensity of illumination over a surface.  One lux is one lumen of light spread over one square meter.

Silent night, dark night

The night is supposed to be dark.

How dark? If there is an overcast sky with no moon and only the light of stars, we have 0.0001 lux. If there is a full moon, and the sky is clear, we get 0.27 lux. By way of comparison, street lights are at 320 lux and homes at 80 lux.

So what’s the problem?

We have a biological clock which functions in 24 hour cycles. The rhythms of this clock are called circadian rhythms (circa=about, dies=day), which are affected by periods of light and darkness.

This clock is located in a part of the hypothalamus region of the brain, an area called the suprachiasmatic nucleus. This biological clock sets times for us to fall asleep and to wake up. It also controls the release of hormones by our glands into our bloodstream. The ones we are most concerned about are cortisol and melatonin.

Light at night: bad!

Artificial light exposure at night causes problems with cortisol and melatonin secretion, which affects our health significantly.

Cortisol

This is a very important hormone produced by the adrenal glands. Normally, cortisol levels are higher during the day than at night. But exposure to artificial light at night alters the biological clock, and the rhythm of cortisol levels. This is suspected of having an effect on the quality and duration of sleep, and also on appetite and glucose/fat metabolism.

Cortisol levels are affected by both blue (short wavelength) and red (long wavelength) light.

Melatonin

This is a hormone produced by the pineal gland in the brain. How much of it the body produces depends on how dark it is at night and how much light we were exposed to the previous day.

Melatonin production by the body drops significantly if we are exposed to artificial light between sunset and our going to sleep. Blue light has more of an effect on this than red light. This causes problems with sleep, blood pressure levels, temperature regulation, and also blood sugar levels.

There is also a suggestion that exposure to artificial light at night (and the resulting low melatonin levels) may be associated with an increased risk of breast and prostate cancer.

Low melatonin levels may also be implicated in premature aging and depressed immunity.

Blue light may be helpful during the day, because it can improve mood, attention and reaction times. But at night, this short wavelength light causes problems. Compared to the light of standard bulbs, blue light is five times more powerful in reducing melatonin production.

Sources of blue light

LED TVs, digital clocks, light bulbs, laptops, monitor screens, smartphones, tablets and other similar electronic gadgets emit short-wavelength blue light which reduces melatonin levels.

So what to do?

• Keep your bedroom pitch dark at night.
• Turn off all electronic gadgets which emit light, especially blue light, two to three hours before bed time.
• Use a dim red light, if a night light has to be used. This causes the least suppression of melatonin levels, and the least interference with our biological clocks.
• Avoid watching TV or working on the computer just before going to bed.

In brief, don’t just curse the darkness: embrace it!