PP29TESTING THE USE OF SPECTRALLY TUNABLE LIGHTINGSYSTEMS TO IMPROVE COMFORT, ALERTNESS ANDSLEEP QUALITY IN INDOOR WORKING ENVIRONMENTS
Aleix Llenas et al.
DOI 10.25039/x46.2019.PP29
from

CIE x046:2019
Proceedingsof the29th CIE SESSION
Washington D.C., USA, June 14 – 22, 2019
(DOI 10.25039/x46.2019)

The paper has been presented at the 29th CIE Session, Washington D.C., USA, June 14-22, 2019. It
has not been peer-reviewed by CIE.

 CIE 2019
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without
permission in writing from CIE Central Bureau at the address below. Any mention of organizations or
products does not imply endorsement by the CIE.
This paper is made available open access for individual use. However, in all other cases all rights arereserved unless explicit permission is sought from and given by the CIE.
CIE Central Bureau
Babenbergerstrasse 9
A-1010 Vienna
Austria
Tel.: +43 1 714 3187
e-mail: ciecb@cie.co.atwww.cie.co.atLlenas, A. et al. TESTING THE USE OF SPECTRALLY TUNABLE DYNAMIC LIGHTING SYSTEMS TO IMPROVE ...

TESTING THE USE OF SPECTRALLY TUNABLE DYNAMIC LIGHTING SYSTEMS TO
IMPROVE COMFORT, ALERTNESS AND SLEEP QUALITY IN INDOOR WORKINGENVIRONMENTS
1

Llenas, A.1,2 *, Hurlbert, A.3, Lam, F.4, Manudhane, R.4, Gaurav, G.3, Giddings, J.4, Carreras, J.2
Institut de Recerca en Energia de Catalunya (IREC), Barcelona, SPAIN, 2 Ledmotive Technologies
SL, Barcelona, SPAIN, 3 Newcastle University, Newcastle upon Tyne, UNITED KINGDOM, 4 Arup,
London, UNITED KINGDOM.
* allenas@ledmotive.com
DOI 10.25039/x46.2019.PP29

Abstract
Lighting installations in offices and buildings are typically static and specified in terms of theireffects via the classical visual pathway (e.g. chromaticity or brightness). It is now rec ognisedthat spectral variations in light elicit non-visual effects, including on emotion and cognition, viaa distinct neural pathway, and it is important for health and wellbeing to take these into account.
This article describes the aims and methodology of an experiment designed to test whether
dynamic sculpting of the light spectra in indoor environments, either to mimic natural daylightchanges or achieve particular levels of non-visual vs. visual stimulation, may elicit different
biological and behavioural effects. Subjective and objective measurements are used to assess
the behavioural responses resulting from exposure to custom-made, dynamically changing light
spectra sequences that are produced by a spectrally tunable lighting system, and to compare
these with responses to a traditional fluorescent lighting system. The viability of the study isqualitatively evaluated here; quantitative results will be reported el sewhere.
Keywords: spectrum, colour, LED, metameric, CCT, melanopic lux, melanopsin , lighting, smart
lighting, tunable, multi-channel

1 Introduction
The modern human visual system evolved under exposure to natural daylight only, for millennia.
Natural daylight is a mixture of light from the sun and sky, containing energy at all wavelengths
in the visible spectrum. Since the invention of the candle, perhaps 2500 years ago, humans
have become more reliant on artificial lighting technologies , and increasingly so in the past
century after the development of electric light, with more activities being performed indoors,significantly shortening the daily exposure to natural light.
In the design of illumination for indoor spaces, it has traditionally been only the well-establishedvisual effects of light that are considered, such as illuminance, glare, chromaticity or correlated
colour temperature (CCT), and colour rendering indices (e.g. CRI or TM-30). Yet the recent
discovery of the intrinsically photosensitive retinal ganglion cells as the origin of the non-visual
pathway that entrains biological rhythms to the light/dark circadian cycle (LUCAS et al., 2014)(BERSON et al., 2002) has started a new drive to characterise lighting in terms also of its non visual effects on human behaviour. This non-visual pathway is responsible not only for
regulating the circadian rhythms of body temperature, melatonin secretion, and the overall
sleep/wake cycle, but also for modulating cognitive function, attention, and mood (CAJOCHEN,
2007) (CHELLAPPA et al., 2011) (BADIA et al., 1991). Although it has long been known thatthe entraining light signal emanated from the retina (SCHEER, 1999) (LEWY et al., 1980) it was
not until the discovery of the ipRGCs (BERSON et al., 2002) (VANDEWALLE et al., 1996) andthe characterisation of the melanopsin photopigment they contain that the importance ofspectral variations in light for eliciting non-visual effects was fully recognised. The spectral
sensitivity of melanopsin peaks at 480 nm, midway between the short- and middle-wavelength
cones, but is broad-band and overlaps with that of all four classical photoreceptors. Modulationof the short-wavelength (“blue”) content of light has been shown to affect various physiologicalmeasures such as melatonin suppression, alertness, thermoregulation, heart rate, cognitive

830

Proceedings of 29th CIE Session 2019

Llenas, A. et al. TESTING THE USE OF SPECTRALLY TUNABLE DYNAMIC LIGHTING SYSTEMS TO IMPROVE ...

performance, and electroencephalographic dynamics (BONMATI-CARRION et al., 2014)(REVELL et al., 2007).
The effectiveness of a given light spectrum in activating the non-visual pathway may bequantified by its melanopic lux, the spectral irradiance weighted by the melanopsin spectral
sensitivity function and integrated over wavelength (Lucas et al. 2014), or by functions of thesame (e.g. CS, REA et al. 2010). Melanopic lux is therefore an appropriate characteristic of
illumination to consider in addition to visual factors such as photopic lux or CCT.
Currently, the most common artificial light sources are fluorescent lights and white LEDs which
are all static sources with spectra very different from natural daylight. The recent invention of
narrow-band LEDs enables the development of spectrally tuneable light sources that are able
to generate illuminations with arbitrary spectral shapes, and therefore to mimic daylight spectral
patterns or create tailored dynamic spectral sequences according to the end -user needs(SCHUBERT, 2005).
Previous studies have compared the performance of individual subjects under different artificial
lighting conditions (e.g. VIOLA et al., 2008). Such studies, though, have used only two types ofwhite light, both fixed in time: cool blue-enriched fluorescent light and warm fluorescent light,
and have not exploited the novel spectral flexibility obtainable from multi-channel LED lightsources.
In this study, and for the first time in a real office setting, the behavioural effects of a dynamic
spectrally tunable lighting system are investigated and compared to a traditional fixed
fluorescent lighting system. The study includes assessments of alertness, mood, sleep quality,
performance, mental effort, and other responses to different dynamic illumination conditions in
a 9-week intervention using subjective and objective measurements.

2 Experiment design
This experiment aims to investigate the effects of novel spectrally tunable light-engines that
produce custom-made dynamic illumination sequences during daytime workhours in an officesetting. The aim is to assess whether sculpting different spectral power distributions (SPDs) oflight may bring measurable benefits in terms of well-being and productivity in an indoor
workplace installation, and, more generally, to understand better the behavioural effects ofdifferent lighting conditions in indoor environments and raise awareness of the importance of acircadian lighting approach.
This investigation took place from February 18 th to April 19 th 2019 at a multinational professional
services firm headquartered in London, United Kingdom. An area of approximately 160 square
meters was selected, comprising the working desks of 24 people. A set of 36 downlighter
luminaires containing LEDMOTIVE (model VEGA07) tunable light engines were installed into
ceiling panels alongside the pre-existing fixed fluorescent light tubes. External light sourceswere blocked by completely covering the windows along one wall, and inserting a scrim between
this space and the adjacent working area (see Figure 1).

Proceedings of 29th CIE Session 2019831

Llenas, A. et al. TESTING THE USE OF SPECTRALLY TUNABLE DYNAMIC LIGHTING SYSTEMS TO IMPROVE ...

Figure 1 – Photograph of the office with Ledmotive’s spectrally tunable lighting systeminstalled.
The habitual start and end time of the workday are 08:00 and 18:00, respectively. Sunrise varied
from 07:09 at the beginning of the study period to 05:57 at its end; dusk varied from 17:20 to
20:03. Thus, for most of the study, dawn and dusk happened outside the workhours, andexposure duration to light during this period, including the commute time to and from work, will
have varied from the beginning to the end of the study.
The study duration was 9 weeks. The lighting conditions were: first, 2 weeks under the preexisting traditional fluorescent lights only (baseline); second, 2 weeks under the spectrally
tunable light sequence A; third, 2 weeks under the spectrally tunable light sequence B; fourth,
1 week of the spectrally tunable lights mimicking the baseline traditional fluorescent lights
output; and, lastly, 2 weeks under the spectrally tunable lights mimicking the current daylightpatterns. Light sequence A had temporally changing melanopic lux, photopic lux and CCT
during the day, with melanopic lux falling from a high of 45 0 in the morning to a low of 160 in
the evening, photopic lux falling from 500 in the morning to 300 in the evening, and the CCTchanging from cool (6000) to warm (2500) over the same interval. Light sequence B matchedlight sequence A in terms of its changing melanopic lux, but kept constant photopic lux and CCT
at levels matching the baseline fixed fluorescent lights. Table 1 summarizes the different light
conditions and the parameters (CCT, photopic lux and melanopic lux) that remain static orchanging.
Table 1 – Summary of the trial’s light conditions.
Light condition

Duration

DatesthPhotopic lux

Melanopic lux

CCTBaseline (Fluorescentlights)2 weeks

February 18 toMarch 3rd

Static (350 lx)

Static (160 lx)

Static (3534 K)

Sequence A

2 weeks

May 4th to May
17th

Changing (500 lx– 300 lx)

Changing (450 lx– 160 lx )Changing (6000
K – 2500 K)

Sequence B

2 weeks

March 18th toMarch 31th

Static (350 lx)

Changing (450 lx– 170 lx)

Static (3534 K)

Baseline (mimicking
fluorescent lights)

1 weekApril 1st to April
7th

Static (350 lx)

Static (160 lx)

Static (3534 K)

Real-time daylightmatching

2 weeks

April 8th to April
19th

Changing

Changing

Changing

832

Proceedings of 29th CIE Session 2019

Llenas, A. et al. TESTING THE USE OF SPECTRALLY TUNABLE DYNAMIC LIGHTING SYSTEMS TO IMPROVE ...

15 employees (age range 25 – 57; 6 males), having diverse roles within the company,
volunteered to take part in the study. All participants completed health screening
questionnaires, including screenings for sleep disorders, depression, anxiety, physical illness,and extreme chronotypes; none were excluded on the basis of these assessments. All gave
their written informed consent prior to any study procedures. The participants were not informedof the specific lighting conditions to be used or the expected outcomes of the study.

3 Subjective and objective measurements
Throughout the study period, each participant took part in daily subjective and objective
behavioural assessments as follows.

3.1 Subjective measurements
Participants were asked to complete web-based questionnaires at four timepoints (1-4) each
weekday (Monday-Friday), and at two timepoints (1 and 4) on each day of the weekend(Saturday-Sunday) and holidays. Specifically:

Waking (timepoint 1): Sleep diary, morning entry: after waking up, participants
completed questions assessing the quality of the previous night’s sleep.

Morning (timepoint 2): Between 10:30 and 11:00h, participants completed aquestionnaire combining the Karolinska Sleepiness Scale (KSS) (AKERSTEDT et al.,1004) (GILLBERG et al., 1994), the Rating Scale Mental Effort (RSME) (VERWEY et al.,1996) and Positive and Negative Affect Scale (PANAS) (CRAWFORD et al., 2004).

Afternoon (timepoint 3): In mid-afternoon (16:00h), participants were asked to repeat
the combined questionnaire of KSS, RSME and PANAS.



Evening (timepoint 4): Before going to sleep, participants were asked to completequestions about sleepiness, mood, drinks and exercise during the day, and to assess
their level of headache and eye strain.

Every Friday, participants were also asked to complete questions on their subjective experienceof the lighting condition experienced that week.

3.2 Objective measurements
Subjective assessments were complemented with objective measurements. More specifically:Actigraphs recordings: All participants were asked to wear a wearable smart watch
24/7 that keeps track of temperature, light exposure and activity levels.



Short perceptual experiments: Participants completed a short (5 minutes) visual
attention task at two timepoints (2 and 3) each weekday. The task was a continuous
performance task which assessed sustained attention, implemented via a web-based
JavaScript application, presented in black-and-white.

4 Light conditions
4.1 Baseline
The light conditions set for the first two weeks were regular fluorescent lights, some of the mostused light sources in the world. Its spiky spectrum (see Figure 2, left) is very well -known andtotally different from natural daylight. The office’s fluores cent lights had a CCT of 3550K andtypical values of photopic lux at the desktop were about 350 lx. The melanopic lux for this light
was about 160 lx at the desktop. During the 7 th week, when mimicking fluorescent lights withthe spectrally tunable light source (see Figure 2, right), the light generated had the same
parameters: CCT of 3550K, photopic lux of 350 lx and melanopic lux of 160 lx at the desk level.
Figure 3 shows that with these light conditions, the three indicators remain static during thewhole working day.

Proceedings of 29th CIE Session 2019833

Llenas, A. et al. TESTING THE USE OF SPECTRALLY TUNABLE DYNAMIC LIGHTING SYSTEMS TO IMPROVE ...

Figure 2 – Baselines: Real fluorescent lights SPD (left) and spectrally tunable light engine SPD(right). Both measured spectra have the same CCT of 3550K, same photopic lux of 350 lx andsame melanopic lux of 160 lx at desk level.

Figure 3 – In an office setting with only fluorescent lights, light indicators such as CCT,
photopic lux or melanopic lux coming from the light fixtures remain static during the wholeworking day.

4.2 Light sequences
The LEDMOTIVE (model VEGA07) tunable light engine used for this experiment is composedof 48 commercial monochromatic LEDs arranged in 7 channels, each with a distinct peakwavelength, spread over the visible spectrum (see Figure 4).

Figure 4 – CIE 1931 xy coordinates of the 7 channels that define the colour gamut (a) and thepreset SPDs of the 7 LED channels (b).

834

Proceedings of 29th CIE Session 2019

Llenas, A. et al. TESTING THE USE OF SPECTRALLY TUNABLE DYNAMIC LIGHTING SYSTEMS TO IMPROVE ...

High melanopic lux in the morning is thought to lead to better attention and higher arousal,
while low melanopic lux in the evening is suitable for relaxing and for better sleep at night (TEKULVE et al., 2017). This experiment adds to the existing knowledge by using spectrally tunable
light systems with light sequences tailored to human needs. In this experiment, light sequence
A was designed to change in CCT from cool in the morning to warm in the afternoon, and withphotopic and melanopic lux values changing from high values in the morning to low values in
the afternoon (see Figure 5). Sequence B was designed with the same visual parameters asbaseline (same CCT and same photopic lux) but with changing melanopic lux values during theday (see Figure 6). By comparing sequence B with baseline, the experiment compared theeffects of changing melanopic lux alone, with the other parameters remaining the same. With
sequence A, we are able to test not only the melanopic lux effect, but also the effect of aconcomitant changes in CCT, as the visual comfort and overall experience that the light fixtures
evoke is also important for well-being.

Figure 5 – (left) Sequence A was designed to have a changing CCT, changing photopic lux andchanging melanopic lux during the day. (right) In-situ measured spectra from Sequence A
SPD, varying from 9 am (blue) to 6 pm (red).

Figure 6 – (left) Sequence B was designed to have the same static CCT and photopic lux asbaseline during all the day, but with changing melanopic lux. (right) In-situ measured spectrafrom Sequence B SPD, varying from 9 am (blue) to 6 pm (red).

4.3 Real-time daylight matching
During the trial’s final two weeks, a calibrated spectrometer in the building’s roof was installedthat was able to measure daylight spectra every few seconds. The spectrometer, connected toa Raspberry Pi, sends the spectral information to the lighting system co ntrol unit, which, very
fast, finds the channel weights that give the best spectral fitting to the target SPD (LLENAS etal., 2019). Any change in CCT or illuminance in the outdoor environment was smoothlytranslated inside the office.

Proceedings of 29th CIE Session 2019835

Llenas, A. et al. TESTING THE USE OF SPECTRALLY TUNABLE DYNAMIC LIGHTING SYSTEMS TO IMPROVE ...

5 Conclusions
This article elaborates on an experiment that was conducted during 9 weeks in an office setting
without interfering with employees’ daily tasks or normal work-load. Different light conditions
were used to test whether by designing custom-made SPDs of light in a dynamic way, it ispossible to elicit benefits in participant’s sleep patterns, alertness, mental effort and mood. The
final results will be published elsewhere.

References
AKERSTEDT T, HUME K, MINORS D, WATERHOUSE J. The subjective meaning of good sleep,an intraindividual approach using the Karolinska Sleep Diary. Percept Mot Skills. 1994;79(1Pt 1):287–96.
BADIA, P, MYERS, B, BOECKER, M, CULPEPPER, J, HARSH, JR. Bright li ght effects on bodytemperature, alertness, EEG and behaviour. Physiology & Behavior. 1991;50(3):583-8.
BERSON, D, DUNN, F AND TAKAO, M. Phototransduction by retinal ganglion cells that set thecircadian clock. Science 2002; Vol. 295(5557), no. 1070–1073.
BONMATI-CARRION, M. A., MIDDLETON, B., et al. 2014. Circadian phase asessment by
ambulatory monitoring in humans: Correlation with dim light melatonin onset.
Chronobiology International 31(1): 37-51.
CAJOCHEN C. Alerting effects of light. Sleep Med. Rev. 2007; Vols. 11(6), 453–464.
CHELLAPPA, S. L., STEINER, R., BLATTNER, P., OELHAFEN, P., GÖTZ, T., & CAJOCHEN,
C., 2011. Non-visual effects of light on melatonin, alertness and cognitive performance:
can blue-enriched light keep us alert?. PloS one, 6(1), e16429.
CRAWFORD, J. R., HENRY, J. D., 2004. The Positive and Negative Affect Schedule (PANAS):
Construct validity, measurement properties and normative data in a large non ‐clinicalsample. British Journal of Clinical Psychology, 43(3), 245-265.
GILLBERG M., KECKLUND G., AKERSTEDT T., 1994. Relations between performance andsubjective ratings of sleepiness during a night awake. Sleep.;17(3):236–41.
LEWY, A., WEHR, T., GOODWIN, F., NEWSOME, D., AND MARKEY S. , 1980. Light
suppresses melatonin secretion in humans, Science 210 , 1267–1269.
LLENAS, A., CARRERAS, J., 2019. Arbitrary spectral matching using multi-LED lighting
systems. Optical Engineering 58(3), 035105.
LUCAS, R.J., PIERSON, S.N., BERSON, D.M. et al., 2014. Measuring and using light in themelanopsin age. Trends in Neuroscience, 37(1):1-9.
REA, M.S., FIGUEIRO, M.G., BIERMAN, A., BULLOUGH, J.D., 2010. Circadian light. J
Circadian Rhythms, 8(1):2.
REVELL, V. L., & SKENE, D. J., 2007. Light‐induced melatonin suppression in humans withpolychromatic and monochromatic light. Chronobiology international, 24(6), 1125-1137.
SCHEER, F., DOORNEN, L., BUIJS R., 1999. Light and diurnal cycle affect human heart rate:possible role for the circadian pacemaker. J. Biol. Rhythms; Vol. 14(3), no. 202–212.
SCHUBERT, E. F., 2005. Solid-State Light Sources Getting Smart. Science.
TE KULVE, M., SCHLANGEN, L. J., SCHELLEN, L., FRIJNS, A. J., VAN MARKEN
LICHTENBELT, W. D., 2017. The impact of morning light intensity and environmental
temperature on body temperatures and alertness. Physiology & behavior, 175, 72-81.
VANDEWALLE, G., BALTEAU, E., PHILLIPS, C., DEGUELDRE, C., MOREAU, V.,
STERPENICH, V., ALBOUY, G., DARSAUD, A., DESSEILLES, M., DANG -VU, T.,
PEIGNEUX, P., A. LUXEN, D.-J. DIJK, MAQUET, P., 2006. Daytime light exposure
dynamically enhances brain responses, Curr. Biol. 16, 1616 – 1621.

836

Proceedings of 29th CIE Session 2019

Llenas, A. et al. TESTING THE USE OF SPECTRALLY TUNABLE DYNAMIC LIGHTING SYSTEMS TO IMPROVE ...

VERWEY, W.B., VELTMAN H.A., 1996. Detecting short periods of elevated workload:
comparison of nine assessment techniques. J Appl Psychol Applied.;3(2):270–85.
VIOLA AU, JAMES LM, SCHLANGEN LJ, DIJK DJ., 2008. Blue-enriched white light in theworkplace improves self-reported alertness, performance and sleep quality. Scand J Work
Environ Health.;34(4):297-306.

Proceedings of 29th CIE Session 2019837