Why did NASA change the lights on the space station?

Why do astronauts sleep badly?

The ISS circles the Earth roughly every 92 minutes. That means about 16 sunrises and sunsets a day. The body's internal clock, normally set by daylight, gets no clear signal for when it is day and when it is night.

It shows in their sleep. According to NASA's own researchers, astronauts slept about six hours a night while their schedule allowed eight and a half. Sleeping pills and caffeine were common on board. In a summary for NASA's 2016 research symposium, the researchers described circadian misalignment and disrupted sleep as common on long-duration missions.

What did NASA replace the fluorescent lights with?

The old fluorescent lights, General Luminaire Assemblies, gave the same white light around the clock. They were replaced with Solid State Lighting Assemblies, LED units that can change both intensity and spectrum. The first installation was planned for late 2016, and the switch was still under way in spring 2017.

The units have three preset modes. The figures come from NASA's description of the Lighting Effects study, led by Steven Lockley at Brigham and Women's Hospital and George Brainard at Thomas Jefferson University.

Look at how the modes differ. It is not only brightness that changes, but how much blue the light contains. A lower colour temperature means warmer light with less blue. The pre-sleep mode has both a lower colour temperature and less than a quarter of the brightness of the work mode.

Why does the colour of light matter so much?

The internal clock is set by a special type of cell in the eye that contains the protein melanopsin. These cells are most sensitive to blue light around 480 nm and cannot see images. They only measure whether it is light and how blue the light is. We cover the cell in Your eye's third cell type.

That is why dimming the fluorescent lights was not enough. A dim but blue light still says daytime to that cell. NASA solved it by removing blue in the evening and adding it in the morning.

Can you do the same at home?

In principle yes, and it is exactly what experts recommend. In 2022 an international research group published recommendations for indoor light in PLOS Biology. During the day, the light reaching the eye should be bright, at least 250 lux measured as melanopic illuminance. In the three hours before bed it should be no more than 10 lux, and in the bedroom at night no more than 1 lux.

It is the same logic as on the ISS: lots of light and lots of blue during the day, little of both in the evening. The difference is that you cannot swap every lamp, screen and streetlight you meet on an ordinary evening.

• Daytime: go outside, sit near a window and let daylight reach your eyes.
• Evening: dim the ceiling light and choose lamps with a warm colour temperature, 2700 K or lower.
• The last hours: lower screen brightness and filter the blue that still reaches your eyes.

What does this have to do with glasses?

A lens cannot change the lamp, but it changes the light reaching your eyes from every lamp at once. The orange LOWLIGHT lens filters 98% between 400 and 500 nm. The red filters 99% between 400–550 nm. That is the lens's filtration according to the supplier's spectral measurement, not a promise of better sleep. How the lenses differ is covered in Yellow, orange or red lens.