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Effects of Intensity of Short-Wavelength Light
on the EEG and Performance of Astronauts
During Target Tracking
Yang Gong1, Ao Jiang2(B), ZiJian Wu1, Xinyun Fu1, Xiang Yao1,
Caroline Hemingray2, Stephen Westland2, and WenKai Li1
1Xiangtan University, Xiangtan, Hunan, China
2School of Design, University of Leeds, Leeds, UK
aojohn928@gmail.com
Abstract. In complex human-machine systems such as spacecraft, poor astronaut
performance leads to dangerous accidents, and assessing the functional state of
astronauts during a mission has positive impacts on risk reduction and efficiency.
This paper aimed to assess the functional state of astronauts in performing tar-
get tracking tasks of different difficulty at three different short-wavelength light
intensities (40 lx, 80 lx, and 160 lx) in a simulated space station module with a
head-mounted display (HMD) and electroencephalogram (EEG) equipment, and
collect EEG and task performance changes as well, aiming to better understand the
cognitive behavior of astronauts during spacecraft operations. Thirty healthy par-
ticipants were recruited for this experiment and their EEG physiological signals
were collected during simulated astronauts in conducting target tracking tasks.
Meanwhile, all participants wore a head-mounted display (HMD) to perform tar-
get tracking tasks of low, medium, and high difficulty in three intensities (40 lx,
80 lx, and 160 lx) of short-wavelength light (λmax =475 nm), while remaining in
the darkness (<1 lx). All the participants’ EEG power in the beta range after expo-
sure to 160 lx light was significantly higher than that to 40 lx and 80 lx light, or it
kept in the darkness. In addition, alpha and theta power were significantly lower
in 160 lx light than in darkness. This study provides some evidence that nighttime
short-wavelength light exposure can improve the astronaut task performance in
performing target tracking.
Keywords: Short-wavelength light ·Target tracking ·EEG ·Task performance
1 Introduction
Most tasks performed by astronauts during manned space missions require high levels
of brain activity. Moreover, cosmic radiation, microgravity, and light exposure have
impacts on the astronaut’s brain [1–4]. Therefore, it is particularly important to explore
the factors that affect the brain load of astronauts [2]. The National Aeronautics and
Space Administration (NASA) is focusing its space exploration on the Moon in the
coming years, and other countries are also pursuing more interplanetary exploration
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2022
D. Harris and W.-C. Li (Eds.): HCII 2022, LNAI 13307, pp. 279–289, 2022.
https://doi.org/10.1007/978-3-031-06086-1_21
280 Y. Gong et al.
programs [5]. As various human space exploration missions advance and humans spend
more time in space, understanding the challenges faced by astronauts who live and
work in the space environment and knowing how to address them are important for the
development and planning of future human space missions [6].
Long-term adaptation to the space environment is critical to the health, safety and
productivity of all astronauts [6,7]. When astronauts go to the Moon, Mars and other
planets to carry out complex and diverse space missions, they are susceptible to distur-
bances in the spaceflight environment, thus resulting in increased mental fatigue and
impairing the human ability to process information, which has impacts on the efficiency
of the mission [6,8]. Similar to other human spaceflight activities, as an important
spaceflight operation task, target tracking requires astronauts’ rich experience and pre-
cise operation. Furthermore, due to the reduced concentration, slow thinking or sluggish
movements of astronauts during operations, the target tracking task is performed less
efficiently and may result in in-flight accidents [2].
Some researches on date have revealed that light is not limited to influencing
human physiological parameters and circadian rhythms but also has impacts on neurobe-
havioural performance [1,9,10]. In Lin et al.’s study, all participants were irradiated with
three intensities of short-wavelength light and darkness, all of which revealed signifi-
cant changes in electroencephalogram (EEG) power at different frequencies [11]. Other
studies have proved that higher illumination levels can speed up cognitive responses in
humans and improve task performance [12]. What’s more, Sunde et al.’s study exposed
healthy participants to different wavelengths of light for the assessment of work perfor-
mance, and it was found that participants’ productivity was significantly improved by
using short-wavelength light exposure compared with long-wavelength light [13]. How-
ever, as the effects of different wavelengths of illumination on humans when performing
target tracking tasks were still not discovered at this stage, more researches are clearly
needed to discover the effects of intensity of short-wavelength light on brain activity and
task performance.
To better understand the effects of different intensities of short-wavelength light on
astronaut EEG and task performance, this study used a head-mounted display (HMD)
and EEG equipment to investigate the effects of different intensities of short-wavelength
light on participants’ EEG and task performance, while performing target tracking tasks
of various difficulties in a simulated space station module. Thus, (Q1) does the exposure
to short-wavelength light affect the EEG power and task performance? (Q2) Are there
differences in the effects of different short-wavelength light intensities on EEG power
and task performance?
2 Methods
2.1 Participants
Thirty healthy male participants were enrolled for this trial to participate in the study at
the age of 18–28 years (M =23.5, SD =1.9). All participants were non-smokers without
the history of cardiovascular or cerebrovascular disease or psychiatric disorders. During
the experiment, all participants were required to be in good psychological condition
and avoid smoking, alcohol, and caffeine intake. On the other hand, all participants had
Effects of Intensity of Short-Wavelength Light on the EEG 281
participated in a course on the use of head-mounted displays (HMD). The participants
were briefed on the procedure and precautions before the experiment, and all participants
signed an informed consent form. The experiment was approved by the local ethics
review board.
2.2 Scene Building
Researchers used a joint Rhino and Unity platform to develop the interior scenes of the
crew module of the International Space Station. The program was set up in C# and a
3D computer rendering program was used to simulate the space station module scene
with various color surroundings. The panoramic view is shown in Fig. 1. Reference to
the International Space Station environment, the ceiling, floor, walls are covered with a
primary color, while cabinets, and the processors are decorated with secondary colors.
This method has been used in previous studies [14]. All participants were required to
wear an HMD for viewing, and the handle controller is represented as a virtual hand in
the scene. The virtual hand can be used to perform tasks in the scene.
Fig. 1. Virtual space capsule
2.3 Lighting Conditions
This experiment adjusted the lighting parameters in the control interface in Unity, and
the lighting system in this environment provided spectrally tunable illumination. All
participants were asked to wear an HMD to experiment in the virtual environment.
Four light settings were used for the experiments, including a dim (CCT2000 K,
<1 lx) and three short-wavelength lighting conditions. The short-wavelength condition
had a peak at about 480 nm and was approximately Gaussian with a half-width half-
height of 35 nm. Three intensities were 40 lx, 80 lx and l60 lux (±1 lx). The spectra of the
three test lighting conditions were measured with an X-Rite i1Pro spectro-photometer
282 Y. Gong et al.
(Fig. 2). According to the new CIE S 026/E: 201818, the a-opic irradiance for each
lighting was calculated (Table 1).
Fig. 2. Spectral power distributions of three test lighting conditions
Table 1. α-Opic irradiance (mW/m2) for three lighting conditions and 1 lx daylight (for
reference).
α-opic irradiance for S-cone-opic M-cone-opic L-cone-opic Rhodopic Melanopic
40 lx 157.98 131.44 80.48 277.64 324.25
80 lx 340.38 273.25 167.00 580.18 678.81
160 lx 716.54 557.33 340.56 1187.21 1389.97
1lxD65 0.82 1.46 1.63 1.45 1.33
2.4 Procedures
From November to December 2021, all participants were brought to the lab after 20:00
and each participant completed four sessions over four nights. At the same time, all
participants were fitted with EEG electrodes before starting the experiment. The order
of the conditions (Dim, Blue 40 lx, 80 lx, and 160 lx) was selected randomly for each
participant to avoid potential sequence effects. To avoid potential carry-over effects, the
interval between light experiments of different intensities was at least 72 h, and each
light intensity environment was equipped with low, medium, and high difficulty target
tracking tasks.
In the target tracking mission, the tracking target appeared randomly at any location
in the space station and moved randomly in any way. The higher the difficulty was, the
faster the tracking target moved. The tracking target was a white ball of 65 pixels ×
Effects of Intensity of Short-Wavelength Light on the EEG 283
20 pixels and the tracker was a rectangular target of the same shape of 130 pixels ×
40 pixels (Fig. 3). The participant controlled the joystick so that the on-screen tracker
covered the tracking target until the tracking target was in the center of the tracker and
the tracking target stops moving (Fig. 4).
Fig. 3. Rectangular target and white ball
Fig. 4. One target tracking test completed
After the experiment started, the first 5 min were used to collect the resting-state
signal of the participants, in which the participants were recommended to sit still and
minimize their mental activity. To avoid potential sequence effects, the difficulty of the
target tracking task was randomly selected, and all participants were required to perform
35 tests at each difficulty. The program automatically recorded the time for each test
and took the last 20 test times for calculation, and the average tracking time was used to
measure the participants’ performance.
284 Y. Gong et al.
2.5 Signal Acquisition
EEG data were collected using Brain Vision Analyzer 2.2 Live Software with wire-
less advanced brain monitoring (ABM) EEG device (X10 headset with standard sensor
strips). The recordings consisted of EEG with nine electrode positions (Fz, Cz, Poz, F3,
F4, C3, C4, P3, and P4) and two reference mastoid electrodes. The electrode impedance
test was conducted each time before the experiment to ensure the good conductivity
between the scalp and electrodes, thus obtaining the good quality of the signal. The
EEG signal was band-passed to 1–40 Hz and decontaminated using ABM’s validated arti-
fact identification and decontamination algorithms that identify and remove five artifact
types, namely electromyogram, electrooculogram, excursions, saturations, and spikes.
Power spectral density (PSD) was computed by performing Fast Fourier Transform with
the application of a Kaiser window, and the PSD of selected 1-Hz bins was averaged
after the application of a 50% over-lapping window across three one-second overlays.
2.6 Statistical
All statistical analyses were performed using SPSS 25.0, and one-way ANOVA was used
to explore differences in EEG power between short-wavelength light and the three brain-
wave frequencies of alpha, beta, and theta during target tracking missions, and determine
statistical significance. The Alpha values of 0.05 were considered to be significant. After
testing the static distributivity of the data, HSD post hoc tests of statistical significance
(p <0.05) on these data was performed.
3 Results
3.1 Electroencephalogram (EEG)
A one-way ANOVA on the EEG power data was performed under different intensities
of short-wavelength light and the data displayed significant differences in EEG power
between the three different intensities of short-wavelength light (40 lx, 80 lx, 160 lx) and
the dim condition under alpha, beta, and theta waves (F(1, 1836) =6.24, p =0.002, η2
=0.007). The analysis illustrated that EEG power was more significant (p <0.05) under
light conditions, with more significant (p <0.05) EEG power under short-wavelength
light conditions at 160 lx than at 80 lx and 40 lx, and more significant (p <0.05) EEG
efficiency under 80 lx than under 40 lx. Post hoc tests showing that the higher the intensity
is, the more significant the EEG power is generated by performing target tracking (p <
0.05) (Fig. 5).
3.2 Defferent Frequencies
A one-way ANOVA indicated that the three short-wavelength light intensities at different
frequencies differed significantly (p <0.05) from the EEG power in the dim condition.
There were significant differences between the short-wavelength light intensities of
160 lx, 80 lx, and 40 lx and the dim condition at the alpha wave (F(1, 1044) =54.42, p
=0.000, η2=0.141). At the beta wave, there were significant differences between the
Effects of Intensity of Short-Wavelength Light on the EEG 285
Fig. 5. Mean ±standard deviation of mean normalized EEG power for four light intensities at
different frequencies of brain waves
short-wavelength light intensities of 160 lx and 80 lx, and 40 lx and the dim condition
(F(1, 1044) =54.244, p =0.000, η2=0.116); at theta waves, short-wavelength light
with the intensities of 160 lx, 80 lx, and 40 lx were significantly different from the dim
condition (F(1, 1044) =130.85, p =0.000, η2=0.261). According to post hoc tests,
EEG power was more significant in the light condition than that in the dim condition
(p <0.05). Under alpha and theta waves, low-intensity light was more significant (p <
0.05) than high-intensity light, and EEG power was higher under dim conditions than
that under 40 lx, 80 lx, and 160 lx conditions. In beta waves, high-intensity light was
more significant than low-intensity light (p <0.05), and EEG power was obviously
higher in light conditions than in dim conditions (p <0.05).
3.3 Various Difficulties
Analysis of the data for subjective performance displayed significant differences in task
performance between the three short-wavelength light intensities and the dim conditions
(F (1, 1836) =4.133, p =0.016, η2=0.006). The data indicated that the task performance
under 160 lx light was more significant (p <0.05) than that under 80 lx and 40 lx
light, and 80 lx was more significant (p <0.05) than 40 lx light (p <0.05) for task
performance. The results indicated that high-intensity light improved task efficiency
more significantly (p <0.05) compared with low-intensity light. There were significant
differences in performance for different difficulty tasks in the three short-wavelength
light conditions (F(1, 1836) =3.053, p =0.048, η2=0.004), with more significant
performance for tasks of lower difficulty (p <0.05). The post-hoc tests showed that
EEG power was significantly higher in the light condition than that in the dim condition
for the three different difficulty tasks (p =0.02 <0.05). The task performance was
significantly higher under 160 lx light than that under 80 lx and 40 lx (p =0.026 <
0.05), and the task performance was significantly higher under 80 lx light than under
40 lx light (Fig. 6).
286 Y. Gong et al.
Fig. 6. Mean ±standard deviation of the mean normalized EEG power for the four light intensities
at different levels of difficulties
4 Discussion
The results of this study proved that high-intensity short-wavelength light is a more
effective stimulus than low-intensity short-wavelength light and that it can make the
brains of astronauts on missions more active. In contrast to previous studies that short-
wavelength light could not significantly alter EEG activity in theta waves [15], the present
experiment remarkably increased the EEG power in the alpha and theta bands in all the
three short-wavelength light conditions compared with dim light conditions, where the
lower the intensity of the short-wavelength light was, the higher the EEG power was.
Given that a new study suggested that individual differences at different time periods
have effects on EEG activity following short-wave blue light exposure [16]. Thus, our
choice of experimental time may also have inadvertently interfered with the power of
the alpha and theta EEG bands, and these differences could explain our differences
from previous findings. In the β-band, all the three short-wavelength light conditions
remarkably increased the EEG power compared with the dim light conditions. Different
from under the alpha and theta waves, the higher intensity short-wavelength light in the
beta band was more effective in increasing the EEG power, which could provide findings
that are consistent with the effects of short-wavelength light on EEG in the beta wave
range in the study conducted by Lin et al. [11].
While most previous studies focused on the effects of different short-wavelength
light intensities on EEG and circadian rhythms [10,16], this paper centered on explor-
ing the effects of different intensities of short-wavelength light exposure on task per-
formance. The results for the subjective performance were as expected, with efficiency
in performing different and difficult target tracking tasks correlated with light intensity.
Participants could effectively reduce target tracking task time and improve task perfor-
mance on the three difficult target tracking tasks with high intensity short-wavelength
Effects of Intensity of Short-Wavelength Light on the EEG 287
light (160 lx) compared with dim light conditions and lower intensity short-wavelength
light. The lower intensity short-wavelength light (40 lx, 80 lx) can improve performance
on the medium and high difficulty target tracking tasks compared with the dim light,
while it was not effective in improving performance on the low difficulty target tracking
task, which was significantly different from the high intensity short-wavelength light
(160 lx). Therefore, high-intensity short-wavelength light is a more correct choice than
low-intensity short-wavelength light in improving target tracking task performance. It
was also found that high-intensity light could improve task performance in Smolders’
study, and use the light intensities of 200 lx and 1000 lx for comparison [12].
A limitation of this study is that the experimental environment is somewhat different
from the actual situation, but even small differences may significantly affect EEG and
task performance. This study was conducted on the ground, whereas the microgravity
environment in which the astronauts were exposed during the actual space task in the
real space environment could impair the astronauts’ tracking task performance [17]. It
has been proved that the subjective perception and visual comfort of the operator is
also a potential factor affecting task performance [18–21]. Therefore, task performance
may not be optimized under the influence of the stressors of long-term space, even with
the use of high-intensity short-wavelength light exposure. Furthermore, the space light
environment was created by the combination of natural light and lighting systems, so
if the equipment capable of simulating the effects of natural light was incorporated and
the subjective measurements of current short-wavelength light conditions were made,
the experimental measurements could be more closely aligned to accurate values [18].
The function of current space lighting equipment was limited to supporting astronaut
vision, and it is critical to provide an illuminated environment that can work efficiently
and awaken the EEG [1,22,23] Therefore, the data from this study can still be used as a
potential countermeasure to improve the space lighting system, which could offer effec-
tive support for further in-depth studies on astronaut EEG assessment during missions
and future long-term space exploration. From other perspectives, the improvements in
space lighting systems could also be applied on Earth, which could provide a valuable
reference for the design of optimized home environments and workplaces.
5 Conclusion
The analysis on the results of this study led to the following conclusions: Short-
wavelength light exposure significantly enhanced EEG activity and can improve task
performance. Higher intensity short-wavelength light has better effects than lower inten-
sity short-wavelength light. Future researches on the effects of short-wavelength light
intensity on astronauts may be extended to explore the changes in EEG and mission per-
formance of astronauts during missions due to short-wavelength light exposure. Most
importantly, future extensions are necessary to validate the conclusions drawn from this
study and provide the right direction for optimizing astronaut performance during human
spaceflight missions.
Acknowledgements. We thank the team of IMA, HI-SEAs, Blue Planet Energy Lab, ILEWG at
ESA for support in the preparation of the experiment. This work is supported by a research project
288 Y. Gong et al.
of a research project of the National Social Science Fund of China (No. 20BG115), a scholarship
from the China Scholarship Council and the University of Leeds (No. 201908430166).
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