ISO/TR 9241-610:2022

Ergonomics of human-system interaction - Part 610: Impact of light and lighting on users of interactive systems

This document provides users of interactive systems with a summary of the existing knowledge about ergonomics considerations for the influence of artificial (electric) and natural lighting of environments on humans other than on vision, with a focus on non-image-forming effects. The document can furthermore be used as guidance on the specification of use environments in consideration of non-visual effects of lighting, also called non-image-forming (NIF) functions. Therapeutic use of light and optical radiation is not part of this document.

Ergonomie de l'intéraction homme-système — Partie 610: Impact de la lumière et de l'éclairage sur les utilisateurs de systèmes interactifs

General Information

• Status: Published
• Publication Date: 04-Oct-2022
• ICS: 13.100 - Occupational safety. Industrial hygiene
• ICS: 13.180 - Ergonomics
• ICS: 91.160.10 - Interior lighting
• Technical Committee: ISO/TC 159/SC 4 - Ergonomics of human-system interaction
• Drafting Committee: ISO/TC 159/SC 4/WG 3 - Controls, workplace and environmental requirements
• Current Stage: 6060 - International Standard published
• Start Date: 05-Oct-2022
• Completion Date: 05-Oct-2022

Overview

ISO/TR 9241-610:2022 - "Ergonomics of human-system interaction - Part 610: Impact of light and lighting on users of interactive systems" is a Technical Report from ISO that summarizes current scientific knowledge about how artificial and natural lighting affects humans beyond vision. The focus is on non-image-forming (NIF) effects (for example, impacts on circadian rhythms, alertness, sleep and mood) rather than therapeutic uses of light. The document is intended as guidance for specifying user environments where interactive systems and visual displays can influence human physiology and behaviour.

Key topics

• Non-visual effects of light: evidence that ocular light exposure influences circadian timing, alertness, hormone release and cognitive function.
• Physiology and mechanisms: role of intrinsically photosensitive retinal ganglion cells (iPRGCs) and melanopsin in NIF responses.
• Circadian timing and zeitgebers: how light acts as a Zeitgeber influencing circadian rhythms and the importance of timing, duration and history of light exposure.
• Light at night (LAN): considerations and research findings about exposure to artificial light during dark hours and potential impacts.
• Physical light characteristics: spatial distribution, source location, spectrum, intensity, timing and the contribution of visual displays to overall light exposure.
• Individual differences: chronotype, age and internal circadian time (body time) affecting sensitivity to light.
• Design guidance: how to consider non-image-forming functions in the specification of use environments for interactive systems.

Practical applications

ISO/TR 9241-610 provides actionable background and design guidance for professionals who need to integrate human-centered lighting considerations into interactive systems and built environments. Typical applications include:

• Specifying ambient lighting and task lighting in workplaces with displays to support alertness and healthy circadian entrainment.
• Designing user interfaces and display luminance/spectrum to limit unintended NIF impacts during night shifts or evening use.
• Informing lighting-control strategies (timing, spectrum tuning) in offices, control rooms, healthcare and education.
• Workplace ergonomics assessments and occupational health policies that address light exposure and sleep/alertness.

Who should use this standard

• UX and human factors professionals
• Lighting designers and electrical engineers
• Ergonomists and occupational health specialists
• Architects, facility managers and systems integrators
• Researchers and policy makers concerned with light, health and interactive systems

Related standards

ISO/TR 9241-610 complements other ergonomics and lighting documents (for example, previous parts of ISO 9241 addressing visual environment) and aligns with contemporary guidance on light and health, circadian ergonomics, and lighting engineering.

Standards Content (Sample)

TECHNICAL ISO/TR
REPORT 9241-610
First edition
2022-10
Ergonomics of human-system
interaction —
Part 610:
Impact of light and lighting on users of
interactive systems
Ergonomie de l'intéraction homme-système —
Partie 610: Impact de la lumière et de l'éclairage sur les utilisateurs
de systèmes interactifs
Reference number
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 S c op e . 1
2 Nor m at i ve r ef er enc e s . 1
3 Terms and definitions . 1
4 L ight and lighting — more than just vision . 4
4.1 H ow radiation impacts the human body . 4
4.2 T he role of light for life . 5
4.3 N on-visual effects of radiation . 6
4.4 A n ew definition of lighting . 9
4.5 W hy light is not light and daylight in interiors is different from solar light . 9
4.6 T he role of daylight and solar radiation . 11
5 L ight and circarhythms .11
5 .1 Ba s ic s . 11
5.2 I mportance of light for the circadian rhythm .12
5.3 A n ew perspective on light. 14
5.4 R elation to other zeitgebers. 16
6 L ight at night (LAN) .17
6.1 General . 17
6.2 S tudies of light at night (LAN or ALAN) . 18
7 L ight history (memory effect) .19
8 Phy s ic a l c h a r ac t er i s t ic s .21
8.1 S patial distribution of the source . 21
8.2 L ocation of the source . 21
8.3 L ight spectrum and its role for vision . 22
8.4 L ight spectrum and its role for non-visual effects . 23
8.5 T ime and timing . 24
8.6 I ntensity . 24
8.7 T he role of visual displays . 24
9 I nd i v idu a l d i f f er enc e s .26
9.1 C hronotype . 26
9.2 A ge dependency . 26
9.3 I nternal circadian time (body time) . 27
10 C onc lu s ion s .28
10 .1 A g r e e d f ac t s .28
10 . 2 C ont r over s i a l i s s ue s .28
Annex A (informative) Some useful behaviours of users or beneficial conditions for the
physical environment .30
Bibliography .31
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
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For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 4,
Ergonomics of human-system interaction.
A list of all parts in the ISO 9241 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
ISO 9241-6 was developed to give guidance on the work environment, including lighting to support
vision. Since the discovery of a third sensor in the human eye, ample research has demonstrated
that ocular light exposure, besides supporting visual perception, influences many aspects of human
physiology and behaviour, including circadian rhythms, alertness and sleep, mood, neuroendocrine and
cognitive function.
Users of interactive systems that mostly incorporate at least one visual display are likely to be affected
both by the light generated by their work equipment and by lighting as an environmental factor. New
scientific evidence establishes the fact that light exposure by the work equipment can reach levels of
[1]
the same magnitude as ambient lighting .
Lighting has been defined as the use of light for making things visible since the International Lighting
[2]
Vocabulary of the CIE was published in 1938. In the 4th edition published in 1987, its definition was
[3]
“application of light to scene, objects or their surroundings so that they may be seen”. The role of
lighting has been thoroughly reconsidered in the light of the scientific evidence in the last two decades
[4]
so that the internationally acknowledged definition was changed in the last version. The definition
now reads “application of light to a scene, objects, or their surroundings” (E-ilv 17-29-001).
“… so that they may be seen” has been dropped because of the new, additional role of light. It is required
by scientists as well as practitioners that the design of lighting be performed in consideration of
health effects. Currently, “Light and Health” has become a slogan pointing to the new goal. This can
be characterized as considering and supporting human circadian rhythms governed by the circadian
clock. Although such rhythms have been studied for decades, the discovery of molecular mechanisms
controlling them was awarded the Nobel Prize for Medicine in 2017. The illustration by the Nobel Prize
Committee can also serve as a short description for this document: “This clock [circadian] helps to
regulate sleep patterns, feeding behaviour, hormone release, blood pressure and body temperature.
[5]
A large proportion of our genes are regulated by the clock.” (Figure 1) .
v
a
Best coordination.
b
Fastest reaction times.
c
Highest body temperature.
d
Highest blood pressure.
e
Melatonin secretion.
f
Deep sleep.
g
Lowest body temperature.
h
Cortisol release.
i
Fastest increase in blood pressure.
j
High alertness.
SOURCE The Nobel Committee for Physiology or Medicine. ‘The 2017 Nobel Prize in Physiology or Medicine’
[5]
press release . Reproduced with permission of the copyright holder.
Figure 1 — The circadian clock (also known as the circadian oscillator) and its impacts on our
physiology
It should be noted that the first Nobel Prize in Medicine was awarded in 1903 to Niels Ryberg Finsen for
his contribution to the treatment of diseases with optical radiation.
The new role of light has been considered not only by scientists but also by various institutions that
deal with ergonomics, work organization, safety and health. Due to a high variety of sources that can be
of relevance, this document has been prepared on the basis of documents representing the published
outcome of expert evaluations of literature with a good general agreement, although published with a
time difference of more than a decade. This document has been prepared after studying References [1]
and [6] to [11] and the literature reviewed by their respective authors.
vi
TECHNICAL REPORT ISO/TR 9241-610:2022(E)
Ergonomics of human-system interaction —
Part 610:
Impact of light and lighting on users of interactive systems
1 S cope
This document provides users of interactive systems with a summary of the existing knowledge about
ergonomics considerations for the influence of artificial (electric) and natural lighting of environments
on humans other than on vision, with a focus on non-image-forming effects.
The document can furthermore be used as guidance on the specification of use environments in
consideration of non-visual effects of lighting, also called non-image-forming (NIF) functions.
Therapeutic use of light and optical radiation is not part of this document.
2 Normat ive references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
correlated colour temperature
CCT
temperature of a black body (Planckian) radiator whose perceived colour most closely resembles that of
a given stimulus at the same brightness and under specified viewing conditions
[SOURCE: IEV 723-08-34]
3.2
chronobiology
field of biology pertaining to periodic rhythms that occur in living organisms in response to external
stimuli such as photoperiod
3.3
chronotype
phase relationship of the circadian clocks to the zeitgeber
Note 1 to entry: A person’s chronotype is the propensity for the individual to sleep at a particular time during a
24-h period.
3.4
circadian
biological process that displays an endogenous, entrainable oscillation of about 24 hours
3.6
circannual
biological process that displays oscillation of about a solar year
3.7
colour rendering
effect of an illuminant on the colour appearance of objects by conscious or
subconscious comparison with their colour appearance under a reference illuminant
[4]
[SOURCE: E-ilv 17-22-107, modified — Notes to entry removed.]
3.8
colour rendering index
CRI
R
measure of the degree to which the psychophysical colour of an object illuminated by the test illuminant
conforms to that of the same object illuminated by the reference illuminant, suitable allowance having
been made for the state of chromatic adaptation
[4]
[SOURCE: E-ilv 17-22-109, modified — Notes to entry removed.]
3.9
cone
photoreceptor in the retina containing light-sensitive pigments capable of initiating the process of
photopic vision
[4]
[SOURCE: E-ilv 17-22-002, modified — Notes to entry removed.]
3.10
daylight
part of global solar radiation capable of causing a visual sensation
Note 1 to entry: This definition is used for the purposes of lighting engineering. In physics, daylight is solar
radiation in the range of optical radiation.
[4]
[SOURCE: E-ilv 17-29-105, modified — Notes to entry replaced.]
3.11
daylight factor
D
quotient of the illuminance at a point on a given plane due to the light received directly and indirectly
from a sky of assumed or known luminance distribution and the illuminance on a horizontal plane
due to an unobstructed hemisphere of this sky, where the contribution of direct sunlight to both
illuminances is excluded
[4]
[SOURCE: E-ilv 17-29-121, modified — Notes to entry removed.]
3.12
intrinsically photosensitive retinal ganglion cell
iPRGC
cells in the human retina that are intrinsically photosensitive due to the presence of melanopsin, a light-
sensitive protein
3.13
light at night
LAN
exposure to artificial light during the dark hours of the day
3.14
light
radiation within the spectral range of optical radiation
Note 1 to entry: This definition also covers the use of the term in most disciplines, e.g. medicine, chemistry,
biology.
3.15
light
radiation within the spectral range of visible radiation
Note 1 to entry: Visible radiation is optical radiation capable of causing a visual sensation directly (see E-ilv 17-
[4]
21-003 ).
3.16
luminous colour
colour perceived to belong to an area that appears to be emitting light as a primary light source or that
appears to be specularly reflecting such light
[4]
[SOURCE: E-ilv 17-22-045, modified — Notes to entry removed.]
3.17
luminous intensity
I , I
v
density of luminous flux with respect to solid angle in a specified direction
dΦ
v
I =
v
dΩ
where
Φ is the luminous flux emitted in a specified direction;
v
Ω is the solid angle containing that direction.
Note 1 to entry: Luminous intensity is measured by candela, which is one of the seven SI base units.
[4]
[SOURCE: E-ilv 17-21-045, modified — Notes to entry revised.]
3.18
melatonin
hormone that is produced by the pineal gland
3.19
optical radiation
electromagnetic radiation at wavelengths between the region of transition to X-rays (λ ≈ 1 nm) and the
region of transition to radio waves (λ ≈ 1 mm)
Note 1 to entry: The lower end of the range begins in some regulations and standards at 100 nm. The difference is
irrelevant for this document because both λ ≈ 1 nm and λ ≈ 100 nm are in the range of UV-C radiation.
[4]
[SOURCE: E-ilv 17-21-002, modified — Notes to entry revised.]
3.20
photopic
relating to or denoting vision in daylight or other bright light, believed to involve chiefly the cones of
the retina
3.21
rod
photoreceptor in the retina containing a light-sensitive pigment capable of initiating the process of
scotopic vision
[4]
[SOURCE: E-ilv 17-22-003, modified — Notes to entry removed.]
3.22
spectrum
display or specification of the monochromatic components of the radiation considered
[4]
[SOURCE: E-ilv 17-21-015, modified — Notes to entry removed.]
3.23
use environment
generic term for the physical environment where light and optical radiation is present or intentionally
used
Note 1 to entry: In industrial areas, use environment is called work environment. Since the physical environment
outside the working space is also effective for the items under consideration, the term use environment has been
introduced for the purposes of the ISO 9241 series.
3.24
zeitgeber
environmental cue, such as a change in light or temperature, that entrains or synchronizes an
organism’s biological rhythms, usually naturally occurring and serving to entrain to the Earth’s 24-h
light/dark and 12-month cycles
Note 1 to entry: From the German “zeit” (time) and “geber” (giver).
4 Lig ht and lighting — more than just vision
4.1 Ho w radiation impacts the human body
Radiation, in general, can generate effects in any material if absorbed by it. Radiation or parts of it
reflected or transmitted do not cause any effect, for example a transparent material does not warm up
independently from the level of energy passing through. Cells, tissues and organisms can be affected by
two different categories of radiation, ionising and non-ionising. The distinction is based on the energy
level of the radiated particles. Light, IR, UV and radio waves belong to non-ionising radiation.
NOTE Extraterrestrial UV radiation capable of ionising does not penetrate the atmosphere, whereas electric
sources emitting similar wavelengths are only used for special purposes and are, therefore, not relevant for this
document.
The relevant parts of the spectrum for this document are light (see Figure 3, Figure 4), (non-ionising)
UV and IR. They can cause a variety of responses after entering the body through three pathways
[12]
(Figure 2).
[13]
Source Çakir, G. Tageslichtnutzung und Sonnenschutzmaßnahmen an Büroarbeitsplätzen. Reproduced with
permission of the copyright holder.
Figure 2 — Pathways for the solar radiation
A plethora of biological effects are caused by optical radiation hitting the skin and the eyes. Depending
on the wavelength, energy can penetrate the skin to a different depth. While vision for which light
is responsible is considered in most publications, generating vitamin D is of vital interest for human
health, not only for the bones but also for the communication between cells (see also 4.5).
4.2 The r ole of light for life
1)
Light is part of the radiant energy that fills the universe. Almost all life on Earth has evolved
accompanied by light. No wonder that most living species have developed biological processes as a
response to the natural light, the availability of which is governed by the rotation of the Earth and its
motion around the sun.
Thus, light is central to the biological history of the world, both as a fuel for photosynthesis and as an
environmental signal. As a fuel for photosynthesis light produces all green life from sea level up to the
highest places where plants can survive, but also all tropical coral reefs deep down to where sunlight
carries sufficient energy. As a signaller, light carries much of the information that enables life to adapt
to its environment, and improved ability to receive that information is responsible for numerous
evolutionary adaptations.
The importance of visible-light signalling for humans is demonstrated, for example, by the exquisiteness
of the eye as an optical instrument; the large fraction (half) of the human brain devoted to visual signal
[14]
processing; and our extreme dependence on visual technologies . In fact, the human eye is not a
sensor that conveys information from the environment to the brain like the ear; it is part of the brain.
At a very early stage of human history, artificial lighting was developed as one of the first human
technologies. It expands the productive day into non-daylight hours and during the day it expands the
productive space into the non-daylight areas of enclosed spaces. Bringing daylight into built space was
one of the main objectives of architecture for thousands of years. Doing so, daylight was manipulated in
different ways even when the “built” environment was a cave.
For the longest part of history, workrooms were built such that artificial lighting served as an auxiliary
means to the main source, daylight. The availability of fluorescent light changed the architecture of
buildings thoroughly, and it was believed that industrial work could be performed even completely
without daylight. But the current notion is that “since the introduction of electric lighting, there has
been inadequate light during the day inside buildings for a robust resetting of the human endogenous
circadian rhythmicity, and too much light at night for a true dark to be detected; this results in circadian
disruption and alters sleep/wake cycle, core body temperature, hormone regulation and release, and
1) Light in this sense is optical radiation.
[15]
patterns of gene expression throughout the body.” Although in the first half of the 20th century the
light inside buildings was less adequate than now, fewer people spent fewer hours in such environments.
With electric lighting becoming ubiquitous, the daily pattern of the light/dark cycle which existed even
in artificially lit interiors to a certain extent has disappeared or can be shifted to other parts of the 24-h
day depending on working hours or personal preferences. However, it is well-known that the light/dark
cycle incident on the retina regulates the timing of the human circadian system. Disruption of a regular,
[16]
24-h pattern of light and dark can significantly affect our health and well-being .
4.3 Non-visual effects of radiation
The solar energy received on the surface of the Earth is part of the radiant energy after being filtered
by the atmosphere. The overall range of wavelengths measurable on Earth extends over a range of
−16 5
wavelengths from 10 m to 10 m (electromagnetic spectrum). Only a limited range of wavelengths of
radiation from 380 nm to 780 nm is considered light by definition in lighting engineering because these
enable the eye to form images by exciting visual sensation, a process called vision. In contrast to these,
some other effects of radiant energy are called “non-visual”.
NOTE There is some confusion in the naming of effects caused by optical radiation other than vision. Since
the 1920s, when disciplines dealing with the impact of “light” on humans became separated, various effects
that did definitely not relate to vision were attributed to photobiology. Thus, some researchers used the phrase
“biological effects” until it was acknowledged that also vision is biological. Before the discovery of the ipRGC
[17]
in 2002, NIF effects of light were called "light effects" . The term NIF effect (non-image-forming effect) was
coined by Küller in 1983 to cover effects other than vision. But it is still possible to find expressions like “non-
image-forming (NIF) biological effects of light” in scientific publications.
In many publications, effects mediated by melanopsin-containing or intrinsic photosensitive retinal
ganglion cells in the eye are considered “non-visual”. But the subject matter of Reference [7], “the eye-
mediated non-image-forming effects of light”, suggests that the “ability of optical radiation to stimulate
each of the five photoreceptor types that can contribute to retina-mediated non-visual effects of light
in humans”. If only light in the definition of CIE can stimulate the photoreceptors in the eye to name
“optical radiation” instead is at least confusing.
The effects considered in Reference [7] are limited to circadian effects without circannual effects. The
question is whether circannual effects are not eye-mediated. Are they not non-visual? Currently, there
is not even an agreement on how to spell non-visual.
To avoid further confusion, the word “non-visual” is used as an alternative to “NIF” following the
rationale of Reference [18]. If circadian effects in the sense of eye-mediated events are addressed, this
will be indicated.
Key
1 gamma rays, X-rays and ultraviolet light blocked by the upper atmosphere (best observed from space)
2 visible light observable from Earth, with some atmospheric distortion
3 most of the infrared spectrum absorbed by atmospheric gases (best observed from space)
4 radio waves observable from Earth
5 long-wavelength radio waves blocked
NOTE The original legend of the figure uses the term transmittance instead of absorption.
[19]
SOURCE NASA , open source.
Figure 3 — Rough plot of Earth’s atmospheric absorption (or opacity) to various wavelengths of
electromagnetic radiation, including visible light
Optical radiation generally refers to all radiation that can be measured using certain techniques and
equipment (mirrors, lenses, filters, diffraction gratings, prisms). Thus visible, ultraviolet (UV), and
infrared (IR) radiation are collectively considered optical radiation. All parts of the optical radiation
are relevant for non-visual effects, including light. (Figure 4, from Reference [8]).
[20]
SOURCE DGUV (2018). Nicht-visuelle Wirkungen von Licht auf den Menschen. Reproduced with permission of
the copyright holder.
Figure 4 — Ranges of optical radiation within the electromagnetic spectrum
Research findings have demonstrated that optical radiation has the potential not only to affect vision
but also to:
— alter the secretion of hormones, with melatonin being the key hormone as a trigger for many
physiologic processes;
— set and reset the “biologic” time of the individual by influencing the circadian rhythm;
— influence key parameters of the human body such as the core body temperature;
— affect thermal comfort by influencing skin temperature;
— affect brain activities beyond a level that is usual for vision;
— affect heart activities;
— modify the sense of taste;
— influence mood and arousal;
— cause or trigger long-term biological effects such as developing or inhibiting certain types of cancer
or body growth of children.
Many effects have been studied, mostly under laboratory conditions. This is also true for the basic
fundaments of terms and concepts applied in lighting engineering, for example the definition of light. To
determine whether or not they are relevant for use environments for the users of interactive systems
is not a simple task because light governs human life stronger than air or water, both known for being
indispensable for living.
Many of the relevant effects have been studied and were known before the twenty-first century, but
the mechanisms were not clearly known. In photobiology, the study of the interaction of biological
systems with non-ionizing radiant energy in the ultraviolet (UV), visible and infrared (IR) portions of
the electromagnetic spectrum, effects of solar radiation on humans and animals including such wide-
ranging phenomena as damage to ocular tissues, skin effects, tumour formation and the synchronization
of biological rhythms were well-known. A variety of diseases have been treated with visible light or UV
radiation. And a solarium was a sanatorium before our calendar began.
In the year 2002, a sensor in the human retina was detected that is held responsible for effects related to
biological rhythms. The cells are called ipRGCs and are sensitive in the wavelengths of visible radiation,
i.e. light. The ipRGCs are rendered photosensitive through the expression of melanopsin, an opsin-based
[21][22]
photopigment that is most sensitive to light at around 480 nm .
From many biological rhythms in the human body, the most relevant are daily and yearly rhythms.
These do not fully follow the solar rhythm of days or years without the impact of solar radiation and
are therefore called “circa”, circadian and circannual. The exposition to solar radiation triggers those
rhythms to exactly follow, for example, the solar day. Light does not induce the rhythms; its role is
entraining.
Since the study of circadian rhythms is easier than that of circannual rhythms, most references that can
be found in the literature are related to circadian effects. And most studies are performed by measuring
melatonin, the “sleep” hormone, just because of the ease of the measurement. This is only partly useful,
although melatonin is a key hormone whereas the mechanisms leading to circannual rhythms are
widely unknown. The same is true for the relationships between circadian and circannual rhythms.
The lighting of use environments for interactive systems is believed to affect humans beyond the
intended effect of vision. To study them is rather difficult because of the nature of potential effects that
can become effective with some time lag between exposure to radiation and the response. In addition,
a given impact is not only related to the physical characteristics of the source but also to the timing and
duration. This simply means that a certain amount of light will cause different effects depending on
the time of day of exposure. It also means that the same light exposure can cause positive and negative
effects depending on timing.
As explained in this document, a small part of the visible spectrum is responsible for affecting melatonin
secretion or suppression and, thus, for many non-visual effects. Since this part of the spectrum, blue
with a peak of 480 nm, is not suitable for lighting use environments, lighting comprises also other parts
of the visible spectrum. In contrast to regular lighting, this type of spectrum is called “blue-enriched”.
Almost all visual displays used for interactive systems operate also with blue-enriched light. Thus,
separating the contribution of lighting from that of the work equipment is extremely difficult, if ever
possible. What is really different is the role of the lighting equipment the light of which is designed
not to hit the eye directly, but after being reflected whereas the light of a visual display is the intended
signal, and the human eye focuses on that while working.
The known or possible effects of lighting and optical radiation in humans were evaluated in 2011 to
[12]
detect the need for activities in standardization or legislation .
4.4 A new definition of lighting
The improved knowledge about the impacts of light as described in this document made it necessary to
change the definition of one of the oldest human technologies, lighting.
Lighting has been defined by the CIE since 1938 as “lighting – application of light to a scene, objects, or
their surroundings so that they may be seen” (International Lighting Vocabulary Term 845-09-01, see
Reference [3]).
[4]
The definition of 2011 no longer includes vision as the goal of lighting . Now, it reads “E-ilv term 17-29-
001 lighting – application of light to a scene, objects, or their surroundings”.
4.5 Wh y light is not light and daylight in interiors is different from solar light
By physical means, light is measured by intensity (e.g. illuminance) and colour (spectrum). All units
to characterize the quantity (i.e. photometric quantities: illuminance, luminance, luminous intensity,
luminous flux) are derived from the corresponding physical units by adjusting them using the spectral
2)
sensitivity of the human eye.
2) The sensitivity of the human eye is represented by the V(λ)-curve as defined by CIE.
Traditionally, time does not play a role in lighting, all quantity and quality criteria are independent
of time. Only for special applications, for example light exposure on a film, time has to be considered.
The reason is that all concepts, units or other considerations in lighting are based on the definition
3)
of light that serves vision. Not all scientific disciplines use the term light in this sense. For vision in
static environments, the actual situation is relevant. The only time dependency is related to the state of
adaptation.
For dealing with the eye-mediated non-visual effects of light, it needs to be considered that the effects
[7]
depend on the timing and the duration of the light exposure .
In lighting technology, it was believed that the spectrum does not play an important role as long as the
impact (luminous colour) is the same because the eye has only rods and three types of cones as sensors.
The human eye would not be able to discriminate between colour sources with the same perceived
colour. For this reason, the illuminance requirements of lighting standards usually do not consider
the spectrum. Thus, certain levels of illuminances are required independently from the spectrum
and colour appearance (luminous colour), and even the latest lighting standard valid for all European
[23]
countries (EN 12464-1) does not specify the colour appearance of the lighting .
Colour vision is not considered part of the visual performance (see Reference [24]), and special care
was given to the light spectrum when colour rendering was deemed essential. For all the rest of use
environments, lighting with lamps that are only capable to render a small set of colours to a certain
degree is being considered sufficient. The “Colour Rendering Index” is not a feature of the lighting but a
characteristic of the lamps used.
For dealing with all non-visual effects of light, the spectrum of the radiation including UV and IR is
essential. Light, IR and UV form the range of the optical radiation in the electromagnetic spectrum.
Daylight in general use of the term is radiation of solar origin regardless of the environment where it is
being used. In lighting engineering, however, it is defined differently from the general notion: “part of
[4]
global solar radiation capable of causing a visual sensation” (E-ilv 17-29-105) . No human or plant will
ever be exposed to “daylight” in the sense of this definition. Solar radiation comprises light and other
parts that are believed not to contribute to vision. But they are effective in the biological sense.
Solar radiation does not only vary depending on the time of day and year in quantity but keeps changing
throughout the day including its spectrum. The composition of “daylight” in the sense of solar radiation
depends on various factors like latitude, time of day, time of year, geographic orientation and altitude.
Therefore, it can only be considered for design purposes under certain assumptions.
In built environments, the change in quantity is obvious and calculated, for example, using the daylight
factor (D) which can vary between 10 in exceptional cases and below 1 in areas that are not adequately
lit by daylight (D = 1 is 1 % of the illuminance measured outside the building). What is not obvious, and
therefore widely neglected, is the filtering effect of the glazing. The best available (but not necessarily
usable) glass not only absorbs and reflects more than 8 % of the incident light, it also filters the
spectrum that the colour rendering is affected (R = 100 > R ≤ 90). This is valid only for a single layer of
a a
thin glass used in tropical areas. Glazing used in moderate climate zones absorbs up to 70 % of incident
light and changes the spectrum such that the colour rendering can suffer considerably. Materials used
in modern buildings can reduce CRI between 97 and 77 while the transmission of visible light can be
[25]
reduced between 69 % and 29 % .
While older types of glazing can be able to transmit some UV, modern glasses filter UV almost entirely
(see Reference [26]). IR is filtered out together with some of the red parts of the spectrum. Thus,
“daylight” in built environments lacks UV and IR compared to solar radiation outside buildings. Given
the fact daylight in the sense of its technical definition does not comprise these parts of the solar
radiation the quality of it before and behind the glazing seems comparable. But this is not true in
consideration of non-visual effects. Even the crucial lack of UV behind glass remains unnoticed for most
lighting experts or health and safety officials.
3) See definition of light at https:// cie .co .at/ eilvterm/ 17 -21 -012.
It should be noted that the CIE Illuminants such as D65 which is being used as the basis of the
calculations of eye-mediated non-visual effects include UV from 300 nm. Some part of the UV (usually
340 nm to 370 nm) serve vision indirectly through the excitation of optical brighteners often used to
enhance the appearance of colour of fabric and paper, causing a whitening effect.
Treating “daylight” in the meaning used in lighting engineering means a misconception of the impact of
light on humans. The Technical Memorandum prepared by the IES Light and Human Health Committee,
therefore, uses the term optical radiation when referring to biological responses other than the visual
[9]
ones . The Memorandum recommends the use of the term light only if the effect under consideration is
related to vision. Also the revision of this document after 10 years includes the same recommendation
(see Reference [10]): “Technically, the term optical radiation should be used to describe the portion of
the electromagnetic spectrum spanning ultraviolet, visible, and infrared radiation that stimulates all
4)
these biological responses.”
4.6 The r ole of daylight and solar radiation
The fact that studies on non-visual effects of artificial lighting outnumber those on the effects of natural
light does not mean that they were much more important. The opposite is true. Since the 1950s when
chronobiology became popular, there is no doubt that the sun is the main zeitgeber. And even in the
1960s, the majority of people over the world would expose themselves to sunlight even if they worked
9 to 5 in buildings. For example, they would walk longer distances than today because the number
of cars was much smaller. Computers and data networks did not influence lifestyles, and thus, the
motivation to stay indoors to use electronic media or to play games did not exist. In the course of later
years, artificial lighting with higher levels became affordable and was accompanied by less discomfort
through glare and heat. Thus, the need to leave the enclosed spaces has diminished.
But compared to the intensity of light and radiation outside, even high levels of artificial lighting can
be considered “dark”. Most workplaces in industrial countries are lit with 500 lx and less, and in other
parts of the world, such levels are not even feasible. Because of the usual direction of the artificial light,
from ceiling to floor, the level in the eye is 200 lx or even less. For a user with a relaxed position of the
head and the eyes, i.e. 35° below horizontal (see ISO 9241-5:1998, Figure 1), the illumination level can
be around 100 lx. Whereas in rooms with windows day
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