Impact of Everyday Light Exposure Patterns on Metabolic, Cardiovascular, and Psychological Health in Younger and Older Adults
Phase: NA
Conditions: Healthy Male and Female Subjects, Healthy Elderly
Sponsor: RWTH Aachen University

 
 
 
 
 
 
 
 
 
Studienprotokoll 
 
 
Titel der Studie: 
 
Impact of everyday light exposure patterns on metabolic, 
cardiovascular and psychological health in younger and older adults 
Akronym: AgeLight 
 
(October 2024) 
 
 
 
 
 
Projektleiter: 
 
Dr. Jan-Frieder Harmsen 
 
Lehr- und Forschungsgebiet Healthy Living Spaces 
Institut für Arbeits-, Sozial- und Umweltmedizin 
RWTH Aachen - Universitätsklinikum 
Pauwelsstraße 30 
D-52074 Aachen 
 
 
 
 

 
 
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Inhaltsverzeichnis 
0. 
DEUTSCHE SYNOPSE ...................................................................................................................................... 3 
1. 
BACKGROUND .............................................................................................................................................. 4 
2. 
AIM OF THE STUDY ........................................................................................................................................ 5 
3. 
STUDY DESIGN .............................................................................................................................................. 5 
4. 
RESPONSIBILITIES .......................................................................................................................................... 6 
4.1. 
INVOLVED CENTRES ................................................................................................................................... 6 
4.2. 
INVOLVED RESEARCHERS ............................................................................................................................ 6 
4.3. 
FINANCING ............................................................................................................................................. 7 
4.4. 
REGISTRATION ......................................................................................................................................... 7 
5. 
PARTICIPANTS .............................................................................................................................................. 7 
5.1. 
INCLUSION CRITERIA ................................................................................................................................. 7 
5.2. 
EXCLUSION CRITERIA ................................................................................................................................. 7 
5.3. 
SCHEDULING ........................................................................................................................................... 7 
5.4. 
RECRUITMENT ......................................................................................................................................... 8 
6. 
METHODS ................................................................................................................................................... 8 
6.1. 
STUDY TIMELINE ...................................................................................................................................... 8 
6.2. 
PARTICIPANTS AND GROUPS ....................................................................................................................... 8 
6.3. 
STUDY COMPONENTS ............................................................................................................................... 8 
6.3.2 
EYE EXAMINATION .................................................................................................................................... 9 
6.3.3 
QUESTIONNAIRES ................................................................................................................................... 10 
6.3.4 
SMARTPHONE-BASED AMBULATORY ASSESSMENT ......................................................................................... 11 
6.4 
MEASUREMENT DEVICES ......................................................................................................................... 12 
6.4.1  
ACTLUMUS WEARABLE LIGHT SENSOR ......................................................................................................... 12 
6.4.2 
CONTINUOUS GLUCOSE MONITORING ......................................................................................................... 13 
6.4.3 
ECGPRO HOLTER-RR USB ...................................................................................................................... 13 
6.4.4 
IBUTTON THERMAL SKIN SENSOR ............................................................................................................... 16 
6.5 
FLOWCHART AND SCHEDULE .................................................................................................................... 16 
7 
RISKS ........................................................................................................................................................ 17 
8 
STATISTICAL ANALYSIS .................................................................................................................................. 18 
8.4 
PRIMARY AND SECONDARY STUDY PARAMETERS ........................................................................................... 18 
9 
ETHICS ...................................................................................................................................................... 19 
9.3 
RECRUITMENT AND CONSENT ................................................................................................................... 19 
9.4 
SAFETY REPORTS .................................................................................................................................... 19 
9.4.2 
ADVERSE EVENTS (AES) ........................................................................................................................... 20 
9.4.3 
SERIOUS ADVERSE EVENTS (SAES) ............................................................................................................. 20 
9.4.4 
FOLLOW-UP OF ADVERSE EVENTS .............................................................................................................. 20 
10 
DATA PROTECTION ...................................................................................................................................... 20 
11 
INSURANCE ................................................................................................................................................ 21 
12 
COSTS, INCENTIVES AND LOSS OF EARNINGS ..................................................................................................... 21 
13 
SIGNATURE ................................................................................................................................................ 21 
14 
REFERENCES .............................................................................................................................................. 22 
 
 
 
 

 
 
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0. Deutsche Synopse 
Menschen verbringen die meiste Zeit in Innenräumen unter suboptimalen Lichtverhältnissen, 
was zunehmend als Risikofaktor für die steigende Häufigkeit von Herz-Kreislauf-, 
Stoffwechsel- und psychischen Erkrankungen in der alternden Gesellschaft angesehen wird. 
Lichtexposition kann den Blutzucker, den Blutdruck und das psychische Wohlbefinden 
beeinflussen. Daher können schlechte Lichtverhältnisse im Alltag zu der zunehmenden 
Belastung des Gesundheitssystems im Zusammenhang mit einer alternden Bevölkerung 
beitragen. Außerdem ist bekannt, dass die Lichtempfindlichkeit im Alter abnimmt (z. B. 
aufgrund der altersbedingten Degeneration der Augenstrukturen), was positive 
gesundheitliche Auswirkungen von Licht abschwächen kann. Derzeit ist jedoch weitgehend 
unbekannt, wie sich die Lichtexpositionsgewohnheiten und die Sensitivität gegenüber den 
gesundheitlichen Auswirkungen von Licht mit dem Alter verändern. Ebenso ist unklar, 
inwieweit Unterschiede in der Lichtempfindlichkeit von der Degeneration der Linse und der 
Netzhaut abhängen. In dieser Studie sollen alltägliche Lichtverhältnisse jüngerer und älterer 
Erwachsener charakterisiert und im Zusammenhang mit kardiovaskulärer, metabolischer und 
psychischer Gesundheit betrachtet werden. Konkret wird ein ambulanter Erhebungsansatz 
über 12 Tage angewendet, bei dem physiologische Parameter und alltägliche Gedanken, 
Verhaltensweisen und Erfahrungen verschiedener Altersgruppen mit Hilfe von tragbaren 
Technologien (z. B. Lichtsensoren, Aktivitäts-Tracker, kontinuierliche Blutzuckermessgeräte) 
und Smartphone-basierten Selbstberichten (z. B. Stimmung, Vitalität) gemessen werden. Zu 
Beginn der Studie wird die Degeneration der Linse und der Netzhaut der Teilnehmenden 
durch Augenärzte objektiv quantifiziert. An den letzten zwei Tagen werden die 
Teilnehmenden in randomisierter Reihenfolge einen Arbeitstag bei schwachem und einen 
weiteren bei hellem Licht unter demselben Messprotokoll wie zuvor verbringen, sodass jede 
Person sowohl einen Bürotag bei schwachem Licht und einen Tag bei hellem Licht verbringt 
(randomisiertes 
Cross-over 
Design). 
Auf 
diese 
Weise 
wird 
die 
individuelle 
Lichtempfindlichkeit und deren gesundheitliche Auswirkungen experimentell bewertet. Die 
Teilnehmenden erhalten als Aufwandsentschädigung nach Beendigung der Studie 200 € und 
bekommen zudem Rückmeldung über ihre alltäglichen Blutzucker- und Blutdruckwerte, 
sowie eine detaillierte Augenuntersuchung. Dieses Projekt wird dazu beitragen, den Einfluss 
von Licht auf Gesundheitsparameter im Alltag besser zu verstehen und langfristig gesunde 
Beleuchtungskonzepte in verschiedenen Gebäudetypen für unterschiedliche Altersgruppen 
zu ermitteln.  
 

 
 
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1. Background  
Within a day, the Earth rotates once around its own axis, causing predictable changes in light 
conditions throughout the day. In this context, humans have developed the ability to 
synchronize their physiological processes to a period length of around 24 hours, adapting to 
these recurring fluctuations. Our ambient light hence has a major influence on our physiology 
and psychology depending on the time of day. However, over the last century our relationship 
to light has drastically changed: our current “indoor society” spends about 90% of awake time 
indoors exposed to lower light intensities (e.g. up to 300 lux for typical electric office lighting) 
than outside in natural daylight (e.g. up to 100,000 lux on a sunny day), along with excessive 
exposure to artificial light during the evening beyond sunset. Yet, studies on the impact of 
daytime light exposure patterns are limited (Fleury et al., 2020). A chronic lack of daylight in 
combination with excessive light in the evening is increasingly being considered as a risk factor 
in the aging society's rising incidence of cardiovascular, metabolic, and psychological 
disorders. For example, experiencing darker days and brighter nights was associated with a 
higher risk for the onset of several psychological disorders such as depression or psychosis 
(Burns et al., 2023). In terms of short-term effects on potential mediating mechanisms, 
Harmsen et al. previously showed that bright light during office hours induced mostly 
favorable acute effects on glucose control and thermoregulation in older insulin-resistant 
volunteers compared to dim light (Harmsen et al., 2022) and that natural office lighting 
through windows improved glucose control in older type 2 diabetes patients (Harmsen et al., 
2022). Similarly, when workers were exposed to higher levels of light during their workday, 
they reported increased vitality and lower depressive symptoms (Mariana G. Figueiro et al., 
2017; Nagare et al., 2021). However, to date, there is only limited data on how light exposure 
patterns differ across the lifespan (Scheuermaier et al., 2010) and how aging may affect the 
influence of light on our physiology and psychology. First findings indicate that younger and 
older adults show different emotional effects of exposure to blue light  (Sletten et al., 2009), 
but these differences have so far not been addressed in daily life.  
 
Growing evidence suggest that the effects of light on health parameters vary dramatically 
across individuals, yet recommendations for appropriate light exposure in real-life settings 
rarely take these individual differences into account (Chellappa, 2021). In this context, age 
has been identified as a moderator of light sensitivity (Chellappa, 2021), but the underlying 
mechanisms remain elusive. Therefore, this interdisciplinary project will for the first time 
explore the contribution of aging processes within the eye to an individual’s sensitivity to light 
and its health effects. The degeneration of the lens associated with cataract is a natural aging 
process that affects the amount of light that can reach the retina. Cataract affects around 
17% in the general population worldwide and up to 54% in the over-60 age group (Hashemi 
et al., 2020). Replacing the lenses of the eye by surgery largely restores light transmission and 
has been shown to improve the sleep-wake rhythm, the release of the sleep hormone 
melatonin, light sensitivity, and sleep quality (Brøndsted et al., 2017; Giménez et al., 2016). 
Depending on how far the degeneration of the lens and retina have progressed and/or 
whether surgical intervention has taken place, large individual differences in sensitivity to 
different ambient light can therefore be expected. However, this aging process is ignored by 
most previous attempts to study the physiological and psychological health effects of light. 

 
 
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2. Aim of the study  
With the primary hypothesis of this study being that younger and older individuals differ in 
their light exposure patterns in everyday life, the two main goals of the AgeLight study are to: 
• characterize light exposure patterns in younger and older adults and their link to 
cardiovascular, metabolic, and psychological health  
• identify determining factors of an individual’s sensitivity to light and its health effects 
(such as degeneration of the lens and retina) 
3. Study design 
This study is designed as an observatory field study of characterizing younger and older adults’ 
everyday life in terms of light exposure patterns as well as cardiovascular, metabolic and 
psychological health parameters over 10 days continuously through wearables and 
smartphone-based self-reports (ambulatory assessment period). On the first day of data 
collection, each participant will undergo an eye examination at the Institute of 
Ophthalmology. Thereafter participants start wearing the wearable sensors and instructions 
on how to complete the smartphone-based self-report forms are provided. Data will be 
collected from the first evening onwards (ca. 18:00 h). After the ambulatory assessment 
period under free-living conditions, participants will spend the 11th and 12th day in a 
controlled office room environment from 08:30 to 17:00 h. In a randomized cross-over design, 
the 11th and 12th day will be spent in either bright (1250 lux) or dim office lighting (10 lux). On 
these days, participants will continue to wear the wearables and complete the same 
smartphone-based self-reports as over the 10-day ambulatory assessment period. Between 
day 11 and 12, participants will leave controlled conditions from 17:00 h on day 11 to 08:30 
h on day 12. On day 11 and 12, participants will receive a standardized fluid meal for breakfast 
and a bread-based meal for lunch, and are otherwise instructed to avoid any food, caloric or 
caffeinated beverages between 08:30 and 17:00 h. After removing all wearables on day 12, 
the study ends at 17:30 h. Over these 12 days of data collection, participants will be asked to 
keep their bedtimes at home as consistent as possible between days, and on day 11 and 12 
they will be instructed to come to the office facilities fasted without any caloric intake after 
22:00 h on the previous evening of day 10 and 11, respectively. 
To minimize the burden on participants in this study, we use mobile and user-friendly devices 
for data collection and give clear instructions for data collection. We keep individual 
assessments short, limit the study duration to 12 days and provide incentives for participation 
(up to €200 reimbursement). On day 11 and 12, participants are mostly free to do whatever 
they like to do while being in the office environment (e.g. watching movies, paperwork, 
reading, video-meetings etc.). 
 

 
 
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4. Responsibilities 
4.1. Involved centres  
The AgeLight study is led by the Institute for Occupational, Social and Environmental 
Medicine at the University Hospital RWTH Aachen in collaboration with the Institute of 
Ophthalmology (also Faculty 10), and the Institute of Psychology (Faculty 7).  
The responsible entity is: 
1. 
University Hospital RWTH Aachen 
Institute for Occupational, Social and Environmental Medicine 
Teaching and research area Healthy Living Spaces 
Pauwelsstr. 30 |  52074 Aachen 
And partners are: 
2. 
Institute of Ophthalmology 
Faculty 10 (Medicine) 
Pauwelsstr. 30 |  52074 Aachen 
3. 
Institute for Psychology 
Faculty 7 (Philosophy)  
Dennewartstr. 25 – 27  |  52068 Aachen 
 
4.2. Involved researchers  
Main responsible: 
Dr. Jan-Frieder Harmsen, Institut für Arbeits-, Sozial- und Umweltmedizin 
 
Leading researchers: 
Prof. Dr. Marcel Schweiker, Institut für Arbeits-, Sozial- und Umweltmedizin 
Fig.1. Overview of study design. 

 
 
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Dr. Anna Jori Lücke, Institut für Psychologie 
Prof. Dr. Andreas Neubauer, Institut für Psychologie 
Prof. Dr. Peter Walter, Klinik für Augenheilkunde 
Dr. Sabine Baumgarten, Klinik für Augenheilkunde 
Prof. Dr. Thomas Kraus, Institut für Arbeits-, Sozial- und Umweltmedizin 
4.3. Financing 
The project is funded by the Federal Ministry of Education and Research (BMBF) and the 
Ministry of Culture and Science of the State of North Rhine-Westphalia (MKW) as part of the 
Excellence Strategy of the Federal and State Governments, supplemented by funds from the 
LuF Healthy Living Space (basic funding of the endowed professorship funded by VILLUM 
FONDEN, Tobaksvejen 10, DK-2860 Soborg, Denmark, (https://veluxfoundations.dk/en) a 
Danish foundation. 
4.4. Registration 
The study will be registered on osf.io. 
5. Participants  
30 healthy younger adults and 30 healthy older adults. 
5.1. Inclusion Criteria  
• Age: 18-35 or 60-80 years old  
• Voluntary participation, signed consent form 
• Owns an Android or iOS Smartphone compatible with the m-Path App 
• Generally healthy (self-reported) 
• Non-smoker for at least 12 months (self-reported) 
5.2. Exclusion criteria  
• Pregnancy (for female participants) (self-reported) 
• Night-shift worker 
• Eye diseases (e.g. glaucoma, age related macular degeneration, diabetic retinopathy 
conditions after retinal detachment / retinal blood vessel occlusions) 
• Pseudophakic eyes 
• Psychological disorders: insomnia, depression, bipolar disorder and generalized anxiety 
disorder 
• Wearing specially-filtered glasses 
5.3. Scheduling  
The 12 days of testing will take place after an initial phone call screening. Participants can 
leave the study at any time for any reason if they wish, without any consequences. The 
investigator may decide to remove a participant from the study for urgent medical reasons. 
Participants may be removed from the study if they do not adhere to the study procedure. 
After elimination, there is no follow-up examination of the participant. In case of withdrawal 
due to medical complications, the participant is referred to a general practitioner. 

 
 
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5.4. Recruitment 
Participants are recruited via advertisements on billboards at the RWTH Aachen University 
Hospital and in newspapers as well as websites. 
6. Methods  
6.1. Study Timeline 
The study will be conducted between November 2024 and May 2025. 
6.2. Participants and Groups 
The two comparative groups formed in this study consist of 30 younger adults (18-35 years) 
and 30 older adults (60-80 years), both females and males will be included, and the aim is to 
match both groups with respect to sex (i.e. ideally 15 women and 15 men per group). The age 
contrast in the two groups is chosen, as substantial differences in degeneration of the lenses 
and retina within the eye can be expected. 
 
For the sample size calculation of n = 30 per group, we refer to Zauner et al. (Zauner et al., 
2023), who created a procedure to calculate statistical power and required sample size for 
wearable light-logging data. For most light-logging metrics, their approach shows that for 
strong differences in light exposure patterns (i.e., winter vs. summer) even smaller samples 
are sufficient (n = 3-24). We do not expect that differences between age groups are that 
strong as seasonal differences. However, we are confident that effects of about d = 0.7 could 
be detected with our design (n = 30 per group).  
 
6.3. Study Components 
6.3.1. Phone call screening  
The phone call screening will take place after participants have received the participant 
information. During the phone call screening process, potential participants will receive a 
short overview of the study and have a chance to raise questions. Once all questions have 
been answered, several key factors will be assessed to determine participants’ eligibility by 
both the inclusion and exclusion criteria. Additionally, more comprehensive information will 
be gathered that is required for a smooth execution of the upcoming experiment.  
1. 
Date of birth, including age, year, and month, but excluding the specific day. 
2. 
Gender. ☐Female ☐Male ☐Diverse ☐Do not want to answer 
3. 
Body weight in kg. 
 
4. 
Height in m. 
5. 
Healthy in general? ☐Yes ☐No  
6. 
Any heart or vascular disease1? ☐Yes ☐No  
7. 
Take any medication2? . ☐Yes ☐No  
7.1. 
If yes: Has any change in the intake3 in the last 3 months? ☐Yes ☐No  
7.2. 
If so, which ones, how often, since when and in what dosage?  
 
1 e.g. high blood pressure, heart failure, diabetes, ... 
2 e.g. painkillers, beta-blockers, thyroid medication, insulin, ADHD medication 
3 dosage, frequency 

 
 
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8. 
Drink alcohol? ☐Yes ☐No  
8.1. 
 
If so, how many units4 per week? 
9. 
Take drugs? ☐Yes ☐No  
10. 
For female participants: pregnant or breastfeeding? ☐Yes ☐No  
11. 
Hours of work each week. 
12.  
Did you have cataract surgery? ☐Yes ☐No 
13.  
Have you been diagnosed with any eye disease? ☐Yes ☐No 
14.  
Have you been diagnosed with any psychological disorder? ☐Yes ☐No 
15.  
Do you have sleep problems? ☐Yes ☐No 
16.  
Involved in shift work? ☐Yes ☐No 
 
17.  
Wearing specially-filtered glasses? ☐Yes ☐No 
18.  
Do you possess a smartphone? ☐Yes ☐No 
 
Once participants are eligible based on the phone call screening, they will be invited for an 
initial visit at the University Hospital to sign the informed consent form, perform the eye 
examination, fill out questionnaires, and provide them with the wearable sensors and instruct 
them on how to complete the smartphone-based self-report forms over the data collection 
period.  
 
6.3.2 Eye examination 
For the eye examination, participants pass different stations on day 1: 
 
1) Objective refraction 
Participants sit in front of the autorefractor and an automated assessment of the refraction 
(sphere, cyclinder, axis) is performed. 
 
2) Testing Visual acuity (distance visual acuity) 
 
sc (sine correctione) 
Firstly, visual acuity is tested “uncorrected”, which is without glasses or contact lenses. 
Participants are positioned in a well-lit area in the standard distance from the visual 
acuity chart (with Landolt rings). The testing distance is typically 6 meters but it may 
vary, for example in smaller spaces. Here, mirrors can be used to achieve the required 
distance. The participant is instructed to cover one eye with the hand or an eye patch, 
and thereafter are asked to read the Landolt rings on the chart. The smallest line they 
can read correctly is recorded. The process is repeated with the other eye covered.  
 
ccs (cum correctione sine) 
The above-mentioned procedure for testing sc visual acuity is repeated, however with 
the participant’s own glasses (if applicable). Each eye is tested separately. 
 
4 glasses 

 
 
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cc (cum correctione) 
Participants are comfortably seated and positioned correctly in front of the phoropter. 
The height of the phoropter is aligned with the participant’s eyes. The phoropter is set 
to its default position, with the lenses set to zero (no correction). Participants look at 
the visual acuity chart and different lenses are presented in order to find the lens 
combination that brings the best visual acuity. In this way best subjective spherical 
and cyclindrical refraction are determined and documented for each eye. Values are 
compared to objective refraction and checked for plausibility.  
 
3) Slit lamp examination 
Participants are seated comfortably in front of the slit lamp. Height and position of the slit 
lamp are adjusted to participant’s eyes. Pupils are not dilated with mydriatic eyedrops. The 
eyes are examined starting with the anterior segment. Especially the lens is investigated for 
its transparency and any signs of cataracts. Lens opacities are documented concerning the 
lens opacities classification system III (LOCS III).  
For posterior segment examination, additional lenses are used (90D) with the slit lamp to view 
the posterior segment of the eye. Any opacities of vitreous or floaters are recorded and retina, 
optic disc, macula and retinal vessels are inspected. All findings are documented and any 
abnormalities are evaluated for potential exclusion criteria.  
 
4) OCT (Optical coherence tomography) examination of the retina 
Participants are positioned in front of the OCT machine. Chin rest and forehead strap are 
adjusted so that the participant’s head is stable and comfortable. The participant is asked to 
look straight ahead at the fixation target inside the machine. The focus of the OCT machine is 
adjusted until a clear image of the retina is visible on the screen. The image is captured and 
screened for any artifacts or distortions and is repeated if necessary. 
 
5) Foveal reflectance analyzer 
Participants will be seated with both forehead and chin supported. They will be instructed to 
look straight forward onto a bright white spot. The macular pigment reflectometer will record 
the difference between the light entering and leaving the eye across the visual spectrum. The 
participant will not notice any of this. Spectral analysis of the reflected light provides an 
adequate estimate of the yellowing of the intra-ocular lens. 
 
6.3.3 Questionnaires 
At the beginning of the study on day 1, participants will complete established questionnaires 
characterizing their typical behaviour and personality traits that may be relevant to better 
understand their light exposure and impacts thereof in daily life. These questionnaires will be 
implemented using the tool SoSci Survey and can be filled out with any device connected to 
the internet. The full list of questionnaires can be found in Table 1. 
 

 
 
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Table 1. List of questionnaires included in the study. 
Questionnaire 
Reference 
Pittsburgh Sleep Quality Index (PSQI) 
(Buysse et al., 1991) 
Light Exposure Behaviour 
Assessment (LEBA) 
(Siraji et al., 2022)  
Munich Chronotype Questionnaire 
(MCU) 
(Roenneberg et al., 2003)  
BFI-K 
(Rammstedt & John, 2005) 
Subjective Vitality Scales (trait) 
(Bertrams et al., 2020) 
Satisfaction with Life Scale 
(Diener et al., 1985) 
Sensorische 
Verarbeitungssensitivität 
(Satow, 2022) 
Assessment of Sleep Environment 
(ASE) questionnaire 
(Grandner et al., 2022) 
 
6.3.4 Smartphone-based ambulatory assessment 
 
The ambulatory assessment will be conducted via the m-Path app installed on the 
participants’ own smartphones. The app is available for Android and iOS smartphones. It will 
prompt participants to fill out a short questionnaire six times per day by sending a push-
notification. And participants will be asked to take pictures of every food or drink (except of 
water) and upload these pictures through the m-Path app. Data from the assessments is saved 
encrypted on a secure GDPR-compliant server in the EU and will be matched to the other 
collected data using a pseudonymized alpha-numeric code.  
 
Table 2. Measures applied in the ambulatory assessment phase. 
All beeps 
 
References 
Affective well-being 
MOOD-zoom + extra items?? 
 
Vitality 
Subjective Vitality Scales (state) 
(Bertrams et al., 2020) 
Alertness 
Karolinska Sleepiness Scale 
(Akerstedt & Gillberg, 1990) 
Daily Experiences 
Stressor Occurrence 
 
 
Uplift Occurrence 
 
Current Situation 
Place 
 
 
Activity 
 
 
Social contact 
 
 
Light sources 
 
 
Perception of current light 
(M. G. Figueiro et al., 2021) 
Morning only 
 
 
Sleep parameters 
CONSENSUS sleep diary 
(Carney et al., 2012) 
Sleep quality 
Adapted PROMIS sleep disturbance 
short form 
 
Evening only 
 
 
Cognitive Function 
2-back task 
As already implemented in m-Path 
Health 
Self-Rated Health 
 
 
Physical Symptoms 
(Larsen & Kasimatis, 1991) 

 
 
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6.4 Measurement devices  
All measurements within the framework of the research project are non-invasive, except for 
placing a continuous glucose monitor on the non-dominant forearm of participants from day 
1 of the data collection period onwards.  
Table 3 shows the different types and respective resolutions of the recorded data.  
 
The continuous glucose monitor and the light sensor will be worn throughout the 12 days of 
the study, while the thermal skin sensors and the ambulatory blood pressure device will only 
be worn on day 11 and 12, between 08:30 and 17:00 h respectively. 
 
 
Table 3. Data collected, methods and resolution. 
Data 
Unit 
Device name 
Frequency 
Skin 
temperature  
°C  
iButtons 
1 min 
Interstitial 
glucose 
mmol/L 
Abbott Freestyle Pro IQ 
15 min 
Illuminance 
Lux 
Melanopic EDI 
Actlumus 
1 min 
Blood 
pressure 
mmHg 
ECGpro Holter-RR USB 
15 min 
 
 
6.4.1  
Actlumus wearable light sensor 
Participants will wear a light logger around the neck like a pendant to log daily light exposure 
levels. The light logger is only worn during the day and taken off at night, or when participants 
get in contact with water (e.g. showering or swimming). We will be using the ActLumus by 
Condor Instruments, which is an actimeter with integrated light logger. The logger estimates 
melanopic EDI and photopic lux through several light channels. The logger is very lightweight 
(12-31 g) and can be clipped to the collar, cloth or worn around the neck or clipped onto 
glasses to measure light at eye-level. Data will be read locally using a cable and transferred to 
our computers (no cloud or external server involved) and analysed with a locally installed 
software from Condor Instruments called ActStudio. 
 

 
 
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6.4.2 Continuous glucose monitoring  
From day 1 to day 12, participants will wear a continuous glucose monitor device on the non-
dominant upper arm. The FreeStyle Libre Pro iQ (Abbott) is a system that can measure blood 
glucose profiles reliably over a period of up to 14 days; it is a standard technique in daily 
diabetes practice. A needle-shaped sensor will be inserted subcutaneously in the skin of the 
arm. Glucose concentrations will be measured every 15 minutes in the interstitial fluid of the 
subcutaneous tissue. These values will be sent to a monitor via a transmitter. 
 
After collecting all the data, blood glucose profiles will be examined for readings that deviate 
from the normal range. If any abnormalities are detected, participants will be notified while 
maintaining rigorous medical confidentiality. 
 
 
 
 
6.4.3 ECGpro Holter-RR USB  
The AMEDTEC Holter ECG (Fig. 4) constitutes a comprehensive long-term ECG system 
designed with an optimal workflow. It efficiently delivers swift and precise analysis of Holter 
Fig.2. Actlumus wearable light-logger 
Fig. 3. Continuous glucose monitor  

 
 
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ECG recordings, available in either 3 or 12-channel modes. Thanks to the device's Auto-
Feedback Logic (AFL), participants experience minimal discomfort. It is capable of recording 
data for multiple days (up to 72 hours) and can store up to 300 measurements. Furthermore, 
it enables the definition of various day and night intervals. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
The ambulatory blood pressure monitoring (ABPM) system AMEDTEC ECGpro Holter-RR, 
created from the ABPM software Holter-RR, manufacturer: AMEDTEC Medizintechnik Aue 
GmbH, CE 0494, and the ABPM recorder device Holter-RR, manufacturer: I.E.M. GmbH, CE 
0044, is a system according to Directive 93/42/EEC, article 12, and complies with the essential 
requirements of MDD 93/42/EEC as well as the regulations of the Medical Devices Act. 
AMEDTEC Medizintechnik Aue GmbH maintains a certified quality management system 
according to DIN EN ISO 13485 and a certificated quality assurance system according to MDD 
93 / 42 / EEC, Annex II.  
The Holter-RR NIBP device complies with the requirements of the ESH (European Society of 
Hypertension) and has a BHS (British Society of Hypertension) A/A grading. AMEDTEC ECGpro 
Holter-RR is a medical device of risk class IIa by MDD 93/42/EEC, annex IX. The device 
complies with the requirements of the applicable standards,  
particularly 
- DIN EN ISO 80601-2-30 „Medical electrical equipment –Part 2-30: Particular 
requirements for the basic safety and essential performance of automated type non-
invasive sphygmomanometers“, 
- DIN EN 60601-1 „Medical electrical equipment – Part 1: General requirements for 
basic safety and essential performance“ and  
Fig.4. ECGpro Holter-RR USB 

 
 
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- DIN EN 60601-1-2 „Medical electrical equipment – Part 12: General requirements for 
basic safety and essential performance – Collateral standard: Electromagnetic 
disturbances – Requirements and tests“. 
After collecting all the data, the heart rate and blood pressure data will be examined for 
readings that deviate from the normal range. If any abnormalities are detected, participants 
will be notified while maintaining rigorous medical confidentiality. 
 
 
 

 
 
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6.4.4 iButton thermal skin sensor 
A wireless temperature system for human skin temperature measurements is described, i.e. 
the iButton (type DS1921H; Maxim/Dallas Semiconductor Corp., USA). The iButton is a small 
(16×6mm2), rugged self-sufficient system that measures temperature and records the results 
in a protected memory section. Afterwards time and temperature data can be transferred 
directly to a computer for data analysis. Four iButtons will be worn by participants on day 11 
and 12 from 08:30 to 17:00 h, respectively. The four iButtons will be placed on the right foot, 
left hand, left chest and neck, as shown in Figure 5 below. They will be attached with self-
adhesive tape. 
 
 
 
 
 
All sensors that will be applied to the participants (i.e., ActLumus, FreeStyle Libre Pro iQ,  
iButtons, ECGpro Holter-RR) are CE-certified and will be used only for their intended purpose. 
 
6.5 Flowchart and Schedule  
After a person expressed interest in participation, researchers will reply by sending the 
information letter and consent form via email. Subsequently, researchers will schedule a 
phone call during which they will provide a brief overview of the key aspects of the 
experiment and address any questions or concerns which participants may have. Additionally, 
this phone call will serve as an opportunity to evaluate participants' eligibility based on the 
inclusion and exclusion criteria (see 6.3.1. phone call screening).  
Following the phone call and scheduling the participation days, participants will sign the 
informed consent form during the first visit at the University Hospital.  
On day 1, each participant will undergo an eye examination and thereafter starts wearing the 
wearable sensors and receives instructions on how to complete the smartphone-based self-
report forms are provided. After the ambulatory assessment period in participants’ everyday 
life (days 2-10), participants will spend the 11th and 12th day in a controlled office room 
environment from 08:30 to 17:00 h. Between day 11 and 12, participants will leave controlled 
conditions from 17:00 h on day 11 to 08:30 h on day 12.  
Throughout these 12 days, the sensors continuously record data until they are removed at 
the end of day 12. Flowchart 1 illustrates this 12-day study period.  
Fig.5. iButton thermal skin sensors  

 
 
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Fig.6.: Flowchart of chronological events of participants enrolment in the study.  
7 
Risks  
Overall, the study ensures that participants are exposed to conditions within the naturally 
occurring limits of daily life. We do not expect any risks from participating in the ambulatory 
assessment with previous research showing high acceptability and no noteworthy reactivity 
to measurement in participants’ behavior. Nevertheless, on day 11 and 12 participants may 
be exposed to light conditions that could be perceived as uncomfortable compared to their 
preferences.  
Blood pressure measurements will be performed on day 11 and 12 by means of an automatic 
inflatable cuff. These measurements might feel a bit uncomfortable, but do not induce 
negative health effects. After wearing the continuous glucose monitor for 12 days, skin 
irritation can occur from where the sensor wire is inserted. 
The eye examinations bring no special risks for participants. Individuals might feel dazzled for 
a few seconds after the slitlamp examination, especially after retinoscopy.  
In summary, there are no side effects, exposures, or complications associated with this study.  
Medical benefits. The study has no direct medical benefit to the participants. However, the 
results form the basis for suggesting improvements in light exposure behaviour for health 
purposes and thus provide a basis for aspects of disease prevention and health promotion. In 
addition, if something abnormal is noted with respect to the eye examination, daily blood 

 
 
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sugar levels and blood pressure, participants will be informed and advised to seek a medical 
health professional.  
Unexpected medical findings. With wearing the continuous glucose monitor and the blood 
pressure cuff as well as eye examinations, there is a small risk of unexpected medical findings. 
These unexpected findings could be revealed based on abnormal blood sugar levels (i.e. 
indicative of type 1 or 2 diabetes mellitus, and hypoglycemia, respectively), or abnormal blood 
pressure levels (i.e. indicative of cardiovascular issues), or eye degeneration (i.e. for which 
surgery could be recommended). In case of such unexpected findings, a physician (Institute 
of Ophthalmology) will inform the individual participant and discuss further steps. Prior to 
such a conversation, the right of the participant not to know is taken into account. 
 
Dealing with COVID-19-related risks. According to WHO, there is no pandemic situation 
(Statement on the Fifteenth Meeting of the IHR (2005) Emergency Committee on the COVID-
19 Pandemic, n.d.). 
8 
Statistical analysis  
8.3 Descriptive statistics 
 
Statistical analysis will be performed using the statistical computer programs SPSS for Mac OS 
(version 25, IBM) and R Studio for Windows. Descriptive statistics will be reported for all data 
parameters and will be reported as minimum, maximum, mean, standard deviation (SD) and 
intraindividual standard deviation (iSD) for data assessed in daily life, and/or standard error 
of the mean (SEM). As a measure of dispersion, SD will be used for descriptive statistics of the 
assessed data, while the SEM will additionally be reported for the results of the primary and 
secondary outcomes.  
In case of non-normality, values will either be transformed using log transformation or non-
parametric tests will be used. In addition, Pearson correlation coefficients will be computed 
to correlate parameter values. The unpaired Students t-test will be used to compare outcome 
measures between the young and old group. Due to the randomized cross-over design, to 
compare outcomes between the bright and dim office light condition irrespective of age 
(secondary outcome), a paired t-test will be conducted. Differences will be considered 
statistically significant when tested two-sided p < 0.05. Missing values will not be replaced. 
We will apply a full information approach using all available data from all participants. 
8.4 Primary and secondary study parameters  
As the primary hypothesis of this study is that younger and older individuals differ in their 
light exposure patterns in everyday life, the primary outcome of this study is melanopic 
equivalent daylight illuminance (M-EDI) quantified in lux by the Actlumus wearable light 
sensor. M-EDI may differ between groups with respect to overall daily levels, exposure levels 
at different times of day (work-day vs. weekend-day), and the difference in exposure levels 
between work-days and weekend-days. Therefore, M-EDI will be statistically analysed 
between groups in the following three ways: 
1. 
Compare the area under the curve (AUC) of M-EDI from day 1 to day 8 between 
young and old (unpaired t-test) 

 
 
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2. 
Averaging exposure levels over work-days and weekend-days in 1-hour time 
intervals over 24 hours and compare the two average 24-hour M-EDI patterns 
between young and old (2-way repeated measures ANOVA, factor 1 (between-
subjects) group, factor 2 (within-subjects) time) 
3. 
Averaging the onset of M-EDI in the morning hours and the offset in the 
evening over work-days and weekend-days and calculate the difference in 
onset and offset between the averaged work-day and weekend-day between 
groups (unpaired t-test) 
The secondary hypotheses are that light exposure patterns in everyday life are linked to daily 
metabolic, cardiovascular and psychological outcomes, and that this link is stronger in 
individuals displaying less degeneration of eye structures.  
Accordingly, mixed effects regression analyses will be performed to assess the relationship 
between different aspects of daily light exposure (momentary M-EDI, average daily exposure 
level, onset/offset; independent variables) and each of the daily health parameters 
(metabolic, cardiovascular, psychological functioning, and sleep; dependent variables). To 
evaluate the role of the degree of eye degeneration, an interaction term between light 
exposure and eye degeneration will be added to the regression models. 
 
9 
Ethics  
The study must be approved by the Ethics Committee of RWTH Aachen University. The study 
is carried out in accordance with the Declaration of Helsinki (the latest version, established in 
Fortaleza, Brazil, 2013) and the Law on Medical Research involving Human Beings (WMO) and 
the General Data Protection Regulation (GDPR or GDPR). 
9.3 Recruitment and Consent  
Participants are recruited via advertisements on billboards of the University Hospital RWTH 
Aachen, public buildings in Aachen, the HLS mailing list, and social media such as LinkedIn and 
Facebook. Potential participants will be informed in writing and orally during an informational 
phone call about the study protocol by the coordinating investigators, and participants can 
contact the researchers at any time if questions arise. Participants who have already 
participated in previous studies and have given written consent to be contacted again for 
future studies (HLS mailing list) will be informed by e-mail. Subsequently, potential interested 
participants will receive participant information documents by email. After at least one day, 
participants can contact the research team by phone, email or in person if they would like to 
participate in the study. During their first visit at the hospital, participants will be asked to 
provide written informed consent after the lead investigator has verified that participants 
have understood the study information and that any open questions have been clarified. 
Participants can terminate their participation in the study at any time without giving a reason 
for their decision. 
9.4 Safety Reports  

 
 
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According to § 10 para. 4 of the WMO, the Principal Investigator will interrupt the study if 
there are reasonable grounds for the continuation of the study to endanger the health or 
safety of the participants. The Principal Investigator shall immediately inform the accredited 
Ethics Committee of any temporary interruption, including the justification for such action. 
The study will be suspended until a further positive decision is made by the accredited ethics 
committee. The research team ensures that all participants are informed.  
9.4.2 Adverse events (AEs)  
Adverse events are defined as any adverse experience that occurs for a participant during the 
study, whether or not it is considered to be related to the experimental intervention. All 
adverse events spontaneously reported by the participant or observed by the investigator or 
his staff are recorded. 
9.4.3 Serious adverse events (SAEs)  
A serious adverse event is any adverse medical event or effect that  
- 
Leads to death; 
- 
Is life-threatening (at the time of the event); 
- 
Requires hospitalization or the extension of an existing inpatient hospital stay; 
- 
Results in persistent or significant disability or inability; 
- 
Is a congenital anomaly birth defect; or 
- 
Any other important medical event that did not result in any of the results listed above 
as a result of a medical or surgical procedure, but could have occurred at the 
reasonable discretion of the investigator. 
Elective hospitalization is not considered a serious adverse event. 
 
The principal investigator shall report to the accredited ethics committee that approved the 
protocol any occurrence of an SAE within 7 days of the first notification for SAEs resulting in 
death or life-threatening, followed by a maximum period of 8 days to complete the initial 
preliminary report. All other SAEs shall be reported within a maximum period of 15 days after 
the first knowledge of the serious adverse events by the principal investigator. 
9.4.4 Follow-up of adverse events  
All SARs are tracked until they subside or until a stable situation has been reached. Depending 
on the event, follow-up may require additional tests or medical procedures if indicated and/or 
a referral to the general practitioner or a specialist. SAEs must be reported by the end of the 
study as defined in the protocol. 
10 Data protection 
The privacy of the participants participating in the study will be protected. This means that 
the study results are associated with a code/number and not with the name of the participant. 
Apart from the research team, only control bodies and the monitoring team have access to 
the research data.  
The key document is secured and password protected; only the Principal Investigator (Dr. Jan-
Frieder Harmsen) and three other Co-Investigators (Dr. Anna Jori Lücke, Prof. Dr. Marcel 
Schweiker and Prof. Dr. Andreas Neubauer) can access the key document. The data are stored 

 
 
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on servers of the University Hospital RWTH Aachen. Anonymized data will be passed on to 
project partners of RWTH Aachen University. Anonymized and partially aggregated date will 
later be deposited in a research data repository. 
 
Participants will receive information about the overall results of this study. This information 
shall be provided orally or in writing. The retention period for the research data will be 10 
years and only the researchers directly involved in the research will have the opportunity to 
access this data. 
11 Insurance 
We do not foresee any additional risks for the participants, as the exposures do not exceed 
naturally occurring daily exposures, so we do not consider subject insurance necessary. For 
the insurance of the way to and from the laboratory, we have provided a route accident 
insurance (“Wege-Unfall-Aufenthaltsversicherung”) under policy number … (will be added 
later). 
12 Costs, incentives and loss of earnings 
For most of the duration of the study, the participants can pursue their everyday life tasks. 
Each participant completing the 12 study days will receive up to 200 € for carrying out the 
entire study. The expense allowance will start at €155 if all parts of the 12-day study are 
completed. Participants receive a bonus of €20 if they answered at least 80% of the six daily 
questionnaires via their smartphone, and another €20 if they answered 90%. If they recruit 
other participants for this study through their social network, they receive another €5. 
 
13 Signature 
Aachen, 09.10.2024 
 
 
 
Dr. Jan-Frieder Harmsen 
 
 
 
 

 
 
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