Monthly Archives: August 2015

A Sci-fi-esque Light-Sensing System

NASA Identifier: iss002-702-085 On Earth, we experience one sunrise and sunset in a 24-hour day. But in a flood of the full spectrum of light, International Space Station crews see about 16 sunrises and sunsets in that same time frame. This sunrise view was taken by the Expedition Two crew in 2010.

NASA Identifier: iss002-702-085
On Earth, we experience one sunrise and sunset in a 24-hour day. But in a flood of the full spectrum of light, International Space Station crews see about 16 sunrises and sunsets in a 24-hour period. This sunrise view was taken by the Expedition Two crew in 2010.

The light sensitivity of the eye’s daytime color vision system evolved later than nonvisual light detection systems and so is not optimized for detecting light to reset the brain’s master circadian clock. On the visible light spectrum, the sensitivity of the three-cone photopic visual system peaks in the mid-wavelength green range, at 555 nanometers. But the nonvisual system contains the photopigment called melanopsin, which has a peak sensitivity at 480 nanometers in the short-wavelength blue range.

In animal models, and studies of different types of blindness, if the visual rods-and-cones system was removed from the cell layers of the eye, or is non-functioning, the nonvisual system works perfectly fine on its own, sending clock-setting light to the brain.

While there is some interaction, circadian neuroscientist Steven W. Lockley explains, the visual and non-visual photoreceptor systems can function independently and have their own photoreceptors, neural pathways and effects on the brain.

It’s crucial that we understand human physiology and our complex relationship with light given how important light is to sleep, circadian rhythms, and health. The eye’s nonvisual retinal system — a sci-fi-esque mechanism of which ophthalmologists largely remain unaware 13 years after the system’s discovery — represents a distinct photoreceptor systems with its own photopigment, neural pathway and function from the photoreception system that we use to see.

Neuroscientist George C. Brainard, director of Thomas Jefferson University’s Light Research Program, was one of the first scientists to study the effects of light wavelength on circadian photoreception. In 2001, his was one of two laboratories that made the major finding about the human eye: the melatonin suppression response — one of the non-visual responses to light — had a peak sensitivity in the blue light range that did not match the light sensitivity pattern of the rods and cones used to see.

Earlier work had shown that total visual blindness did not change circadian light responses, but these papers (Brainard et al., 2001; Thapan et al., 2001) provided more formal functional evidence of a non-rod, non-cone photoreceptor in the human eye.

This discovery, coming on the heels of colleagues’ research showing that the mammalian eye contains a light sensor separate from the visual rods-and-cones system, set up neuroscientist David Berson’s monumental finding in 2002: the mystery photoreceptor and a light-sensitive molecule called melanopsin, discovered in 1998 in the camouflaging skin cells of the African clawed frog, were one and the same.

Unfortunately, the conversation about light wavelengths gets stuck on the short end of the spectrum. It is true that the eye’s nonvisual light-sensing photoreceptor system is most sensitive to short-wavelength blue light, but as Lockley explains, all visible light can affect circadian rhythms. Any light source after dusk can be considered unnatural, including the light necessary to do shiftwork but also the light inside our homes, such as from TVs, cellphones, computers, and other electronic devices, which keeps us awake at night and disrupts our sleep and circadian rhythms.

Light after dusk, as relayed by the eye, tells the brain it’s daytime. And if the brain thinks it’s day, not night, it will induce daytime physiology as it thinks that we are awake at the wrong time. Consequently, light at night shifts the clock, suppresses melatonin, increases heart rate and temperature and alerts the brain — all of which are associated with daytime in a day-active species like humans.

But short-wavelength blue light — a stimulant, as opposed to relaxing, long-wavelength yellow/red light at the far end of the visible light spectrum — is also medicinal light. It can be used to improve alertness, reset disordered clock rhythms, or alleviate seasonal depression.

It’s the natural color of a brilliant, midday sky pouring in through the windows of assisted-care facilities for the elderly, improving patients’ moods, sleep, and cognitive symptoms of dementia.

And it’s a crucial component of the LED lighting wavelength model being tested for the International Space Station.

Space Station Twilight Zone

NASA Identifier: iss002e5413 Night and day don’t exist on the International Space Station, where astronauts live in the equivalent of a twilight zone: Repeated exposure — or lack of exposure — to the wrong wavelengths of light at the wrong time disrupts their biological clocks and circadian rhythms. Still, the views are beautiful: This sunset view with the space station’s solar array in the frame was taken by the Expedition Two crew in 2010.

NASA Identifier: iss002e5413
Night and day don’t exist on the International Space Station, where astronauts live in the equivalent of a twilight zone: Repeated exposure — or lack of exposure — to the wrong wavelengths of light at the wrong time disrupts their biological clocks and circadian rhythms. Still, the views are beautiful: This sunset view with the space station’s solar array in the frame was taken by the Expedition Two crew in 2010.

The International Space Station orbits the Earth every 90 minutes, creating incredible photography opportunities for astronauts who see approximately 16 sunrises and sunsets in a 24-hour period. Night and day don’t exist on the space station, where astronauts live in the equivalent of a twilight zone: Repeated exposure — or lack of exposure — to the wrong wavelengths of light at the wrong time throws their biological clocks out of whack and disrupts their circadian rhythms. The astronauts are cut off from the natural light-dark cycle and therefore have to create their own.

Astronauts typically only get about six hours of sleep in a 24-hour period due to a number of factors, including circadian misalignment. They suffer from insomnia and fatigue: dangerous conditions in space where they are required to work slam shifts — the performance of critical, time-specific operations, such as docking. Sleep loss can severely impair the astronauts’ cognitive functions within a few days, increasing the risk of mission errors and putting their health and safety at risk.

So electric light is coming to the astronauts’ rescue to help with both circadian misalignment and providing an acute stimulant to reduce fatigue in the form of a programmable LED wavelength system being designed and tested by a specialized lighting team of neuroscientists and NASA engineers.

The LED lighting system being designed for the space station will far exceed the sophistication of the aging fluorescent lights now in place. The lighting system is scheduled to be installed in phases, starting in fall 2016 in the U.S. crew quarters and eventually expanding to the entire U.S. module of the space station.

Image courtesy of NASA This educational LED lighting model was prepared to illustrate the full-color spectrum of light that the new, programmable system will provide astronauts — a system that will allow for greater lighting control with the manipulation, or fine-tuning, of color wavelengths.

Image courtesy of NASA
This educational LED lighting model was prepared to illustrate the full-color spectrum of light that the new, programmable system will provide astronauts — a system that will allow for greater lighting control with the manipulation, or fine-tuning, of light’s wavelengths.

No, says neuroscientist Steven W. Lockley, the new LED lights (above) won’t really resemble disco lights. The new, programmable system will provide greater lighting control with the manipulation, or fine-tuning, of the wavelength and intensity of light to either stimulate, when alertness or circadian resetting is required, or not stimulate, for example prior to sleep, the circadian photoreception system. A system of multiple LEDs, he explains in talks, can produce thousands and thousands of combinations of light.

As a countermeasure for fatigue and circadian disruption, and to improve vision, health, safety, and performance, the astronauts will actually see variations of white light, designed to enhance or minimize stimulation as required.

The Rocket Science of Better Light

Photo courtesy of NASA Electric light is coming to the astronauts’ aid in the form of a programmable LED wavelength system. U.S. Astronaut Mike Fincke holds an early prototype of an LED lighting unit that was installed on the space station during Expedition 18 about six years ago.

Electric light is coming to the astronauts’ aid in the form of a programmable LED wavelength system. U.S. Astronaut Mike Fincke holds an early prototype of an LED lighting unit that was installed on the space station.

To work in conjunction with the eye’s nonvisual system, the International Space Station’s high-precision LED lighting system will offer three main settings:

1) high alertness (blue-enriched light): suppresses melatonin, accelerates the shifting of the circadian clock, and boosts reaction times and performance.

2) general illumination: a bright and full spectrum of evenly distributed light — like that of daytime — improves visibility and maintains alertness and cognitive function.

3) pre-sleep, or bedtime (red-enriched white light): de-emphasizes blue light and promotes relaxation and sleep.

The lighting is being designed to help the astronauts relax, sleep, awaken feeling refreshed, and quickly shift their body clocks to better handle dangerous unpredictability in a line of work where one wrong move can mean mortal disaster.

The lights are designed to provide the right light at the right time, from blue-enriched alerting light in the morning, to lighting to maintain good vision during the working day, and then a blue-depleted and lower intensity light before bed to help relaxation and facilitate sleep.

Circadian neuroscientist Steven W. Lockley explains that along with the new lighting, we also need a new way to measure light as the current standards and meters are concerned only with light for vision. Light meters — along with current industry lighting standards — are attuned to the peak light sensitivity of the eye’s daytime color vision system.

The field is designing new ways to describe light so that the nonvisual benefits are also captured, Lockley says, allowing lighting designers and architects to start to incorporate the benefits of light into their designs. The spectral fingerprint of all lighting design should be based on optimizing both the visual and nonvisual benefits of light.

Safety-sensitive occupations, such as those found in the law enforcement and military fields, can benefit from this technology as well. Submarine crews, for example, just like astronauts, lack access to natural light-dark cycles.

A research article published in Acta Astronautica (George C. Brainard, et al., 2012, “Solid-state lighting for the International Space Station: Tests of visual performance and melatonin regulation”) describes the future of lighting.

As the article details, the development of specialized lighting for long-duration space exploration “will ultimately revolutionize how our public facilities, work places and homes are illuminated in the coming decades. … By refining multipurpose lights for astronaut safety, health and well-being in spaceflight, the door is opened for new lighting strategies that can be evolved for use on Earth.”

Everywhere electric light is used, Lockley says, we can do a better job of it. We’re only at the start of understanding what this photoreceptor system does. And as the general public becomes aware of the multipurpose lighting being developed for astronauts, he predicts an explosion in the availability of LED technology on Earth.

NASA Identifier: 259129main_ISS015E18958_full As researchers have written, the development of specialized lighting for long-duration space exploration is helping to open the door for new lighting strategies that can be evolved for use on Earth. The workings of the LED lighting system being developed for the International Space Station hold tremendous implications for myriad lighting applications on Earth.

NASA Identifier: 259129main_ISS015E18958_full
As researchers have written, the development of specialized lighting for long-duration space exploration is helping to open the door for new lighting strategies that can be evolved for use on Earth. The workings of the LED lighting system being designed and tested for the International Space Station hold tremendous implications for myriad lighting applications on Earth.