Quantifying irradiance for eye-mediated non-image-forming effects of light in humans

This Technical Report defines metrics that can be used to evaluate and compare lighting conditions with respect to their potential to achieve non-image-forming, eye-mediated effects of light in human beings. This document applies to visible optic radiation in the wavelength range from 380 nm to 780 nm.
This Technical Report does not give information for particular lighting applications.
This Technical Report does not address health safety issues such as resulting from flicker, photobiological safety or the effects of non-visible optical radiation (ultraviolet and infrared radiation).

Bewertung von Strahlung für nichtvisuelle Wirkungen von Licht bei Aufnahme über die Augen

Diese Norm definiert Maße, die zur Überprüfung und zum Vergleich von Beleuchtungsbedingungen verwendet werden können, hinsichtlich ihres Potentials, nicht bildgebende, durch das Auge übermittelte Einflüsse des Lichts auf den Menschen zu bewirken. Diese Norm stellt außerdem Informationen zur Anwendung in der Beleuchtungspraxis bereit, die sowohl für den öffentlichen als auch den privaten Bereich relevant sind. Allerdings ist der wissenschaftliche Kenntnisstand noch nicht ausreichend ausgereift, um Festlegungen für Beleuchtungsbedingungen zu erstellen, die spezielle, nicht bildgebende Einflüsse auf den Menschen haben. Außerdem liefert diese Norm keine Beleuchtungspraktiken im Zusammenhang mit Schichtarbeit.
Diese Norm befasst sich nicht mit Gesundheitsschutzbelangen, wie sie z. B. durch Flimmern, photobiologische Sicherheit oder die Einflüsse nicht sichtbarer, optischer Strahlung (Ultraviolett- und Infrarotstrahlung) entstehen.

Quantification de l'éclairement énergétique pour les effets non formateurs d'image de la lumière transmise par le biais des yeux chez l'homme

La présente norme définit un système de mesure pouvant être utilisé pour évaluer et comparer les conditions d'éclairage en ce qui concerne leur potentiel d'engendrer des effets non formateurs d'image par le biais des yeux chez les êtres humains. La présente norme fournit également des informations pour une application dans les pratiques en matière d'éclairage, aussi bien dans le domaine public que privé. Toutefois, les connaissances scientifiques ne sont pas encore suffisamment affinées pour permettre l’élaboration de spécifications relatives aux conditions d'éclairage pouvant engendrer des effets spécifiques non formateurs d'image chez les êtres humains. Par ailleurs, la présente norme ne fournit pas d'informations sur les pratiques d'éclairage en relation avec le travail posté.
La présente norme ne traite pas des problèmes de santé et de sécurité tels que ceux résultant d'un papillotement, de la sécurité photobiologique ou des effets des rayonnements optiques non visibles (rayonnements ultraviolet et infrarouge).

Vrednotenje sevanja za ne-slikovne učinke svetlobe pri gledanju

Ta evropski standard opredeljuje merila, ki se lahko uporabljajo za vrednotenje in primerjavo svetlobnih pogojev glede na njihovo možnost za ustvarjanje ne-slikovnih učinkov pri gledanju. Ta evropski standard podaja tudi informacije, ki se uporabljajo pri praksah osvetlitve tako v javni kot v zasebni sferi. Vendar znanost še ni dovolj razvita, da bi se oblikovale specifikacije za svetlobne pogoje, ki lahko ustvarijo določene ne-slikovne učinke pri gledanju. Poleg tega ta evropski standard ne podaja informacij glede praks osvetlitve, povezanih z izmenskim delom.
Ta evropski standard ne zajema zdravstvenih težav, ki so na primer posledica utripanja, fotobiološke varnosti ali vplivov nevidnega optičnega sevanja (ultravijolično in infrardeče sevanje).

General Information

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Published
Publication Date
22-Aug-2017
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
23-Aug-2017
Completion Date
23-Aug-2017

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SLOVENSKI STANDARD
SIST-TP CEN/TR 16791:2017
01-december-2017
9UHGQRWHQMHVHYDQMD]DQHVOLNRYQHXþLQNHVYHWOREHSULJOHGDQMX

Quantifying irradiance for eye-mediated non-image forming effects of light in humans

Bewertung von Strahlung für nichtvisuelle Wirkungen von Licht bei Aufnahme über die

Augen

Quantification de l'éclairement énergétique pour les effets non formateurs d'image de la

lumière transmise par le biais des yeux chez l'homme
Ta slovenski standard je istoveten z: CEN/TR 16791:2017
ICS:
17.180.20 Barve in merjenje svetlobe Colours and measurement of
light
SIST-TP CEN/TR 16791:2017 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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CEN/TR 16791
TECHNICAL REPORT
RAPPORT TECHNIQUE
August 2017
TECHNISCHER BERICHT
ICS 17.180.20
English Version
Quantifying irradiance for eye-mediated non-image-
forming effects of light in humans

Quantification de l'éclairement énergétique pour les Bewertung von Strahlung für nichtvisuelle Wirkungen

effets non formateurs d'image de la lumière transmise von Licht bei Aufnahme über die Augen

par le biais des yeux chez l'homme

This Technical Report was approved by CEN on 2 July 2017. It has been drawn up by the Technical Committee CEN/TC 169.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16791:2017 E

worldwide for CEN national Members.
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Contents Page

European foreword ....................................................................................................................................................... 3

Introduction .................................................................................................................................................................... 4

1 Scope .................................................................................................................................................................... 5

2 Normative references .................................................................................................................................... 5

3 Terms and definitions ................................................................................................................................... 5

4 Non-visual effects of light .......................................................................................................................... 10

4.1 General ............................................................................................................................................................. 10

4.2 Characterization of light regarding non-image-forming effects ................................................. 11

4.2.1 Measurement of spectral power distribution .................................................................................... 11

4.2.2 Determination of each of the photoreceptor inputs ........................................................................ 12

4.3 Pre-receptoral filtering considerations ............................................................................................... 15

4.3.1 General ............................................................................................................................................................. 15

4.3.2 Definitions for age-corrected quantities ............................................................................................. 16

Annex A (informative) Examples of use .............................................................................................................. 19

A.1 Quantifying stimulus to photoreceptors by illuminants ............................................................... 19

A.2 Discussion on cumulated photoreceptor input for non-image-forming effects .................... 22

Bibliography ................................................................................................................................................................. 23

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European foreword

This document (CEN/TR 16791:2017) has been prepared by Technical Committee CEN/TC 169 “Light

and lighting”, the secretariat of which is held by DIN.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent

rights.
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Introduction

There is strong scientific evidence that light is not only essential for vision but also elicits important

biological, non-image-forming effects that are highly relevant for human performance and well-being.

The non-image-forming effects can be either eye or skin mediated (e.g. vitamin D production, skin

cancer or solar dermatitis). This document focuses on the eye-mediated non-image-forming effects.

Depending on time of light exposure, spectral power distribution, duration of exposure, and individual

parameters like circadian phase, light history, and others, light can cause suppression of the nocturnal

release of melatonin, increase heart rate as well as alertness and affect thermoregulation [17], or the

electroencephalogram spectrum. Light is the main synchroniser of the human biological clock. It can

shift the phase of the circadian system and determines the timing of sleep/wake cycle. In a proportion

of patients, light exposure can alleviate seasonal and non-seasonal depression and improve quality of

life [1]. Upon light exposure, fast responses in the range of seconds were seen in the pupillary reflex or

in brain activity.

The current lighting practice and the tendency for energy saving, e.g. European Regulations 244/2009

and 859/2009 as well as 245/2009 and 347/2010 tend to reduce indoor illumination levels. This can

create lighting conditions that are sub-optimal for human well-being, health and functioning.

The above mentioned biological effects of light are elicited by stimulation of ocular photoreceptors. The

receptors for vision, the rods and cones, are relatively well understood and characterized by standards

such as CIE S 017. Although melanopsin containing retinal ganglion cells (intrinsically photosensitive

Retinal Ganglion Cells, ipRGCs) play an important role in the non-image-forming effects of light, this

photoreceptor is not yet included in existing lighting standards and recommendations. Therefore, a

description of optical radiation solely according to the photopic action spectrum is not sufficient. The

actual biological effect to ocular exposure to light will depend on the relative response of all

photoreceptors and there is good evidence for synergistic responses between the receptors. For a

deeper understanding of how a stimulation of the photoreceptors leads to a desirable or undesirable

biological effect, light will be characterized in a way to quantify the input to each of the five known

photoreceptors.

It is also important to recognize the importance of darkness, and the daily pattern of light and dark,

particularly around and during periods of sleep. Additionally, certain changes to the balance of the

spectrum of light at different times of day might be helpful in promoting circadian rhythms [18], but

further evidence would be needed to support this as a general principle. Analysing the involvement of

different photoreceptors would be crucial to understand how such outcomes with impact on human

health are provoked.

The biological non-visual effects of light have a direct impact on human performance and well-being

with large implications for architecture, indoor design, and lighting as well as for social- and work-

schedules. The integration of these effects in lighting applications and designs requires new metrics to

quantify light.

This report contains input of experts that, at the time of writing, also have contributed to the Draft

International Standard in preparation by CIE JTC 9 "CIE system for metrology of ipRGC influenced light

response". This Technical Report is entirely informative in nature and, unlike CIE JTC 9, does not

address field of view aspects. Consequently, insights, terminology, tables (on spectral sensitivity and

age correction) and symbols used in this report may be outdated after publication of the new CIE

standard.
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1 Scope

This Technical Report proposes metrics that can be used to evaluate and compare lighting conditions

with respect to their potential to achieve non-image-forming, eye-mediated effects of light in human

beings. This document applies to visible optic radiation in the wavelength range from 380 nm to

780 nm.

This Technical Report does not give information for particular lighting applications.

This Technical Report does not address health safety issues such as resulting from flicker,

photobiological safety or the effects of non-visible optical radiation (ultraviolet and infrared radiation).

2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

EN 12665, Light and lighting - Basic terms and criteria for specifying lighting requirements

CIE S 017/E:2011, ILV: International Lighting Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given in CIE S 017/E:2011, EN 12665 and

the following apply.

NOTE The differences for definitions of spectrally-weighted quantities that follow the SI convention are given

where applicable.
3.1
α-opic

relating to the characteristics in non-visual photometry of the specified human photoreceptor and its

opsin-based photopigment, denoted by α

Note 1 to entry: The symbol α represents one of the five photopigments. α can take one of five values, set out in

Table 1. See 3.1.1 to 3.1.5.
Note 2 to entry: Based on [13].
3.1.1
S-photopic
relating to S-photopsin, the human S-cone photopigment (α = “sp”)

Note 1 to entry: S-photopsin is sometimes denoted as cyanopsin. In this report the term S-photopic is used to

differ from other publications that are using slightly different sensitivity functions and denoting this sensitivity by

the word cyanopic.

Note 2 to entry: The maximum of S-cone sensitivity is in the blue spectral region at 445 nm. S denotes

maximum sensitivity at short wavelengths.

Note 3 to entry: The function for S-photopic sensitivity is based on the 10° cone fundamentals in CIE 170–

1:2006.
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3.1.2
M-photopic
relating to M-photopsin, the human M-cone photopigment (α = “mp”)

Note 1 to entry: M-photopsin is sometimes denoted as chloropsin. In this report the term M-photopic is used to

differ from other publications that are using slightly different sensitivity functions and denoting this sensitivity by

the word chloropic.

Note 2 to entry: The maximum of M-cone sensitivity is in the green spectral region at 540 nm. M denotes

maximum sensitivity at medium wavelengths.

Note 3 to entry: The function for M-photopic sensitivity is based on the 10° cone fundamentals in CIE 170–

1:2006.
3.1.3
L-photopic
relating to L-photopsin, the human L-cone photopigment (α = “lp”)

Note 1 to entry: L-photopsin is sometimes denoted as erythropsin. In this report the term L-photopic is used to

differ from other publications that are using slightly different sensitivity functions and denoting this sensitivity by

the word erythropic.

Note 2 to entry: The maximum of L-cone sensitivity is in the yellow-red spectral region at 570 nm. L denotes

maximum sensitivity at long wavelengths.

Note 3 to entry: The function for L-photopic sensitivity is based on the 10° cone fundamentals in CIE 170–

1:2006.
3.1.4
scotopic
relating to rhodopsin, the human rod photopigment (α = “rod”)

Note 1 to entry: Scotopic is sometimes denoted as rhodopic. Please note that in [13] the spectral sensitivity for

rods is denoted as “rhodopic”, but the values given there are not equivalent to CIE definitions for scotopic vision.

This is the reason for use of “scotopic” in this document.

Note 2 to entry: The sensitivity function used in this technical report as scotopic is identical to V’(λ), the

sensitivity function of the rods as defined in CIE S010:2005 (ISO 23539).
3.1.5
melanopic
relating to melanopsin, the photopigment contained in human ipRGC (α = “mel”)

Note 1 to entry: The term usually indicates the photoreception of the ipRGCs that is driven by the photopigment

melanopsin. The term “melanopic effects” can be used to denote non-visual effects that are mediated by the

intrinsic photosensitivity of melanopsin containing ipRGCs. Even though melanopsin containing retinal ganglion

cells are present in many different species, the data published here is only valid for humans mainly because of the

inherent ocular transmittance data.

Note 2 to entry: The data used in this report for melanopic sensitivity is based on [13], but the sensitivity

function has been normalized to a maximum that is equal to 1 at 490 nm.

Note 3 to entry: The function for melanopic sensitivity is including the pre-receptoral filtering by the human

ocular system for a reference observer at an age of 32 years.
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3.2
α-opic spectral efficiency (of monochromatic radiation of wavelength λ)
(λ)

spectral sensitivity of one of the five human α-opic photopigments to irradiance incident at the eye’s

outer surface of a standard observer, normalized to the maximum of 1
Note 1 to entry: The unit of the α-opic spectral efficiency is 1.

Note 2 to entry: The spectral efficiency function s (λ) is representing the relative spectral effectiveness of

optical radiation to stimulate the α-opic photopigment at wavelength λ in relation to its maximum effectiveness at

wavelength λ which is defined as 1 for each of the five α-opic photopigments. Equivalent terms for spectral

α,max
efficiency function are “action spectrum” or “spectral weighting function”.

Note 3 to entry: The effectiveness of polychromatic radiation to stimulate the α-opic photopigment is assessed

by spectrally weighting the spectral power distribution of the polychromatic radiation by the spectral efficiency

function as described in 3.3.
3.3
α-opic radiant quantity

spectral radiant quantity weighted with the α-opic spectral efficiency defined by the formula

XX= ∫ λ sdλλ (1)
( ) ( )
e,α e,λ α
where
is the spectral radiant quantity;
X λ
( )
e,λ

is the α-opic spectral efficiency (of monochromatic radiation of wavelength λ) as defined in

s λ
( )
4.2.2, Table 2.

Note 1 to entry: In general X (λ) is a spectral radiometric quantity. E.g. when X (λ) is the spectral radiant

e,λ e,λ

flux (Φ (λ)), X represents the α-opic radiant flux which may be denoted by Φ . In this case the unit for Φ

e,λ e,α e,α e,α
would be W.

Note 2 to entry: In a second example X (λ) could be the spectral radiance. In this case X represents the α-

e,λ e,α
opic radiance which may be denoted by L with units W·sr .
e,α

Note 3 to entry: In this document all integrals are referring to a lower wavelength of 380 nm and to an upper

wavelength of 780 nm, corresponding to the definition range of Table 2.
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3.4
α-opic efficacy of luminous radiation (of a light source)
α,v

quotient of the α-opic radiant quantity of a light source (with known spectral composition) to the

corresponding photometric quantity
∫ X λ ⋅⋅sdλ λ
( ) ( )
e,λα
K = (2)
α,v
KX⋅∫ λ ⋅ V λ ⋅ dλ
( ) ( )
m e,λ

Note 1 to entry: The unit of the α-opic efficacy of luminous radiation (of a light source) is W·lm .

Note 2 to entry: K can be expressed as ratio of the α-opic radiant flux (Φ ) to the luminous flux (Φ )

α,v e,α v
e,α
K = (3)
α,v

When the fluxes are expressed per unit area, Formula (3) equals the quotient of the α-opic irradiance to the

photopic illuminance

Note 3 to entry: For practical reasons it is recommended to modify the unit to W/klm or to mW/lm.

Note 4 to entry: For the special case of a light source with characteristics of standard illuminant D65,

D65
Formula (3) defines the α-opic efficacy of daylight K .
α,v
D65
e, α
D65
K = (4)
α,v
D65
3.5
α-opic irradiance
e,α
α-opic radiant flux per unit area
e,α
E = (5)
e,α
where
F is the area which is uniformly irradiated by Φ
e,α
Note 1 to entry: The unit of the α-opic irradiance is W·m .

Note 2 to entry: α-opic irradiance is usually measured in the outward-facing plane normal to the optical axis at

the outer surface of the eye.
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3.6
α-opic equivalent daylight (D65) illuminance
D65
v, α
D65

illuminance E of a light source with spectral characteristics of standard illuminant D65 that

v, α
provides an equal α-opic irradiance E as the test source
e,α
e,α
D65
E = (6)
v, α
D65
α,v

Note 1 to entry: The unit of the α-opic equivalent daylight (D65) illuminance is lx.

Note 2 to entry: Examples for the melanopic equivalent daylight (D65) illuminance of different light sources at

the same photopic illuminance are given in Table A.2.
3.7
α-opic daylight (D65) efficacy ratio (with luminous radiation)
D65
α,v

ratio of the α-opic efficacy of luminous radiation K of the test light condition (Formula (3)) to the α-

α,v
D65
opic efficacy of luminous radiation of daylight (Formula (4))
α,v
α,v
D65
(7)
γ =
α,v
D65
α,v

Note 1 to entry: The unit of the α-opic daylight (D65) efficacy ratio (with luminous radiation) is 1.

D65

Note 2 to entry: γ can also be expressed as the ratio of the melanopic equivalent daylight illuminance to the

α,v

photopic illuminance of the test light condition. It can also be expressed in percent, where 1 equals 100 %. In this

D65

case the value of the α-opic daylight (D65) efficacy ratio γ in percent is equal to the value of the α-opic

α,v
D65

equivalent daylight illuminance E of a test light condition S that delivers a photopic illuminance of 100 lx.

α,v
D65

Note 3 to entry: For the case that α denotes melanopsin, γ can alternatively be denoted as the melanopic

mel,v

daylight (D65) efficacy ratio (MDER) of the test light condition. In this case MDER should be given as a number

instead of a percentage. Some MDER values for different light sources are given in Table A.2. By multiplying the

photopic illuminance of a test light condition measured in lx with MDER, the value of the melanopic equivalent

daylight illuminance in lx is obtained.
3.8
circadian rhythm
biological rhythm with a period of approximately 24 h

Note 1 to entry: Biological rhythms are endogenous and affect psychology, physiology and behaviour.

Note 2 to entry: The sleep/wake cycle is an example of an endogenous circadian rhythm.

[SOURCE: CIE S 017/E: 2011 17-176; modified: notes to entry added]
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3.9
circadian entrainment

synchronisation of the circadian rhythm of a biological organism to an environmental parameter that

varies cyclically with a period of approximately 24 h

Note 1 to entry: In most conditions the natural (or artificially induced) light-dark cycle is the environmental

parameter that dominates circadian entrainment. Desynchronicity between the endogenous circadian rhythm and

the experienced natural, and/or artificially induced, photoperiod causes disruptions in the sleep/wake cycle (e.g.

jet-lag and shift work).
3.10
intrinsically-photosensitive retinal ganglion cells
ipRGCs

retinal ganglion cells that have intrinsic photosensitivity that is mediated by the photopigment

melanopsin

Note 1 to entry: The ipRGCs are sometimes denoted as photosensitive retinal ganglion cells (pRGCs), or as

melanopsin expressing (or melanopsin containing) retinal ganglion cells.
3.11
non-visual effects
NV effects
non-image-forming effects
NIF effects

eye-mediated light induced physiological and psychological responses or effects of light which are

broadly distinct from visual perception, and are considered to be mainly driven by the ipRGCs

Note 1 to entry: Non-visual (NV) effects of light are sometimes denoted as non-image-forming (NIF) effects of

light. Both terms are equivalent. Another term in use is “biological effects”. Use of this term is not recommended as

also vision is based on biological mechanisms.

Note 2 to entry: Sometimes the term “melanopic effects” is used to denote non-visual effects. Use of this term is

not recommended as a general synonym for NV effects, because it would ignore the influences of other α-opic

photopigments on NV effects.
3.12
melanopsin

photopigment responsible for the intrinsic photosensitivity of ipRGCs, both in humans and in many

animals (α = “mel”)

Note 1 to entry: Sometimes the abbreviation “z” is used instead of “mel” as value for “α” to denote melanopic

effects. “z” is the abbreviation for “Zeitgeber” which symbolizes the influence of melanopic effects on the human

circadian system. It is recommended not to use “z” in order to have a more clear symbol relating to melanopsin

and because also other photopigments may have an influence on the circadian system under certain conditions.

4 Non-visual effects of light
4.1 General

Light is the primary environmental signal that synchronises the endogenous sleep-wake cycle and other

circadian rhythms to the rotation of the Earth. Light exposure is able to shift the rest-activity pattern to

an earlier or later timing in the next circadian cycle. Morning light exposure typically advances the

circadian rhythm, whereas evening light usually delays the circadian rhythm. Apart from these

circadian effects, light can also induce acute changes in human physiology and behaviour, either during

or immediately after the light exposure. Examples include hormone secretion, heart rate, sleep

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propensity, alertness, body temperature, retinal neurophysiology, pupillary constriction, gene

expression and brain responses like neuronal activity or subsequent ability to concentrate [12].

Moreover light has proven to be effective in treating seasonal and non-seasonal depression [2][3][4].

The above circadian and acute effects of light are eye-mediated but the photoreceptive system involved

is not directly related to vision and presents several features that distinguish it from the visual system.

Therefore, they are referred to as non-visual, biological (or non-image-forming, NIF) effects of light. The

spectral sensitivity for nocturnal melatonin suppression in dim light adapted human subjects [5][6] and

aspects of the pupillary light reflex are reported to peak in the blue part of the spectrum, and the action

spectrum cannot be described by the established rod and cone photometric units. Human studies

contrasting blue and green exposures have established greater responses to blue light for some NIF

effects [7][8][9][10]. Taken together, the analysis of studies in humans indicates that for many NIF

effects the sensitivity to light peaks between 460 nm and 500 nm, in the blue-green part of the

spectrum. Examples include changes in the timing of the rhythm of melatonin, acute suppression of

melatonin secretion, elevation of body temperature and heart rate, reduction of subjective sleepiness

and improvement of alertness.

Moreover, the mammalian eye does not require rods and cones for the alignment (entrainment) of

circadian rhythms to the light–dark cycle [11]. A population of directly light-sensitive ganglion cells

within the eye acts to detect the spectral intensity in the blue spectral range, corresponding to

brightness of daylight and suffices to regulate both circadian rhythms and pineal melatonin secretion. It

is now known that a melanopsin containing photoreceptor system in the retina, distinct from the rods

and cones, plays a key role in mediating many of these non-visual, biological effects of light.

Today's lighting standards are based on rod- and cone-photoreception mediated visual aspects of light

only. The recently established melanopsin photoreception pathway is not included in current lighting

metrics and standards. This is an omission as the melanopsin-containing ipRGCs appear to be key

mediators for many non-visual biological effects of light. Therefore, melanopsin-related photoreception

needs to be taken into account when predicting and quantifying NIF effects of light. Rod and cone

photoreceptors can also contribute to NIF effects of light via mechanisms that are still not fully

understood. The interplay of the rod and cones with the ipRGCs is complex and probably varies with the

light intensity, exposure duration, prior light exposure and individual parameters like circadian phase.

A necessary step to enable a deeper understanding of the lighting conditions that lead to a specific

biological response, is to exactly characterize the stimulation of all photoreceptors that make up the

input for the biological system. Scientific studies indicate that all retinal photoreceptors can, under

different conditions, contribute to this input. For many NIF effects the ipRGCs seem to be playing an

essential role. This applies for circadian effects like melatonin suppression, circadian phase shifting or

circadian rhythm stabilization when using typical, daily life, lighting conditions. Also direct alerting

effects of light are known to have a higher sensitivity for shorter wavelengths of light, which is

consistent with the assumption that ipRGCs contribute strongly to these effects.
4.2 Characterization of light regarding non-image-forming effects
4.2.1 Measurement of spectral power distribution

Knowing the spectral power distribution is important for researchers carrying out studies on NIF

effects, for manufacturers developing specific lamp technologies, and for lighting designers, employers

and others who seek to predict the non-image-forming effects of optical radiation in specific

environments.

Spectral measurements are required when the spectral radiance of a source of light is unknown. Often

the spectral irradiance incident on the cornea of the eye is a complex combination of the spectral

irradiance from a number of sources, including light that can be reflected from a number of surfaces.

Such sources can include natural daylight and especially then the spectral irradiance incident on the

cornea of the eye can change with time.
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SIST-TP CEN/TR 16791:2017
CEN/TR 16791:2017 (E)

The spectral irradiance incident on an outward-facing plane normal to the optical axis at the outer

surface of the eye at the cornea shall be determined in the wavelength range 380 nm to 780 nm. For

non-visual effects, the irradiance at the retina is much more relevant than the irradiance at the cornea.

However, a measurement of light at the cornea provides a first useful approximation to estimate the

retinal irradiance of a light condition.

For a detailed assessment of the light situation additional parameters (e.g. luminance, dimensions of the

light source) can be relevant.
4.2.2 Determination of each of the photoreceptor inputs

The systematic set of five quantities to characterize the five photoreceptor inputs that can contribute to

the non-image-forming effects of light are based on the sensitivity functions of the five photoreceptors’

photopigments in the periphery of the retina to irradiance at the surface of the eye is defined in Table 1.

Table 1 — The photoreceptors of the human retina, their designation and formulae
for α-opic irradiance, reproduced and modified
Photoreceptor Photopigment α-opic irradiance α-opic irradiance
(label, α) -2
E (W·m )
e,α
S-cone S-photopsin (sp) S-photopic -2
E (W·m )
e,sp
irradiance
M-cone M-photopsin M-photopic -2
E (W·m )
e,mp
(mp) irradiance
L-cone L-photopsin (lp) L-photopic -2
E (W·m )
e,lp
irradiance
ipRGC melanopsin melanopic -2
E (W·m )
e,mel
(mel) irradiance
Rod rhodopsin (rod) scotopic irradiance -2
E (W·m )
e,rod

The spectral sensitivity functions for the standard human observer are given in Table 2.

The sensitivity for co
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