Blue Light To Stay Awake, Red Light To Sleep

The new Solid-State Lighting Module (SSLM) will replace a fluorescent panel
on the space station. One is seen here held by astronaut Michael Fincke.

One of the tests coming up in the International Space Station is the use of various wavelengths of light to stimulate wakefulness and sleep:

NASA To Test Space-Sleep Colour-Changing Lights

Blue light causes alertness. It's a mechanism behind the light therapy used for depression, which also employs blue light (Light Therapy Edges Out Prozac In Head-To-Head Comparison).

"Studies on Earth suggest humans and other creatures follow what is known as a circadian rhythm - a 24-hour biological cycle involving cell regeneration, urine production and other functions critical to health.

Research indicates that it is regulated by a group of cells in a portion of the brain called the hypothalamus which respond to light information sent by the eye's optic nerve, which in turn controls hormones, body temperature and other functions that influence whether people feel sleepy or wide awake.

When the [Solid-State Lighting Modules (SSLMs)] are coloured blue the aim is to stimulate melanopsin - a pigment found in cells in the eye's retina which send nerve impulses to parts of the brain thought to make a person feel alert.

Blue light is also believed to suppress melatonin - a hormone made by the brain's pineal gland which makes a person feel sleepy when its levels rise in their blood."

But blue light at night can keep us awake. Television and computer monitors give off light in the blue spectrum and are known to disrupt sleep. It looks like red light, or at least less blue light, can improve sleep:

"By switching from blue to red light - via an intermediary white stage - this process should be reversed, encouraging a feeling of sleepiness."
...
"So, varying the spectral composition of light does make sense from a circadian perspective, and better regulating artificial sleep-wake cycles may indeed benefit astronauts' sleep in space."

It seems counterintuitive. I expect red light to rev us up and blue light to calm us down.
________Photo from NASA.