ISO/CIE 8995-1:2025

International
Standard
ISO/CIE 8995-1
First edition
Light and lighting — Lighting of
2025-01
work places —
Part 1:
Indoor
Lumière et éclairage — Éclairage des lieux de travail —
Partie 1: Intérieur
Reference number
© ISO/CIE 2025
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© ISO/CIE 2025 – All rights reserved
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviations . 2
5 Lighting design criteria . 3
5.1 General .3
5.2 Luminance distribution .4
5.2.1 General .4
5.2.2 Average luminance of surfaces .4
5.2.3 Reflectance of surfaces .5
5.2.4 Illuminance on surfaces .6
5.3 Illuminance .6
5.3.1 General .6
5.3.2 Scale of illuminance .6
5.3.3 Illuminances on the task area or activity area .6
5.3.4 Illuminance on the immediate surrounding area .8
5.3.5 Illuminance on the background area .8
5.3.6 Illuminance uniformity .9
5.4 ipRGC-influenced responses to light – Melanopic Equivalent Daylight Illuminance .9
5.5 Illuminance grid .10
5.6 Glare . 12
5.6.1 General . 12
5.6.2 Limiting luminaire luminance . 13
5.6.3 Discomfort glare .14
5.6.4 Veiling reflections and reflected glare .16
5.7 Visual appearance of objects and people within the interior space .16
5.7.1 General .16
5.7.2 Shadows .16
5.7.3 Cylindrical illuminance requirement in the activity space .16
5.7.4 Directional lighting of visual tasks areas .16
5.7.5 Modelling .16
5.8 Colour aspects .17
5.8.1 General .17
5.8.2 Colour appearance of the light source .17
5.8.3 Colour rendering .17
5.9 Temporal light modulation (TLM) .18
5.10 Lighting of work stations with Display Screen Equipment (DSE) .18
5.10.1 General .18
5.10.2 Luminaire luminance limits with downward flux .19
6 Lighting design considerations . 19
6.1 General .19
6.2 Illuminance requirements and recommendations . 20
6.2.1 General . 20
6.2.2 Lighting of the task area or activity area and its immediate surrounding area . 20
6.2.3 Lighting of the space . 20
6.2.4 Variability and adjustability of light .21
6.3 Maintenance factor . 22
6.4 Energy performance . 23
6.5 Daylight . 23
6.6 Room brightness .24

© ISO/CIE 2025 – All rights reserved
iii
7 Schedule of specific lighting requirements .24
7.1 Composition of the tables .24
7.2 Schedule of task areas and activity areas . 25
7.3 Lighting requirements for task areas, activity areas, room and space brightness .27
8 Verification procedures .88
8.1 General . 88
8.2 Illuminances . 88
8.3 Unified glare rating . 88
8.4 Colour rendering and colour appearance . 88
8.5 Luminaire luminance. 88
8.6 Maintenance schedule . 88
8.7 Tolerances in measurements . 89
8.8 System tests . 89
Annex A (informative) Recommended practice regarding implementation of UGR tabular
method for ‘non-standard’ situations .90
Annex B (informative) Additional information on visual and non-visual effects of ocular light
exposure .92
Annex C (informative) Lighting design considerations – Examples .99
Annex D (informative) Commissioning .106
Bibliography .107

© ISO/CIE 2025 – All rights reserved
iv
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
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 274, Light and lighting, in cooperation with the
International Commission on Illumination (CIE).
This first edition of ISO/CIE 8995-1 cancels and replaces ISO 8995-1:2002, which has been technically revised
The main changes are as follows:
— prior document reference numbers (CIE S 008:2002, ISO 8995-1:2002) replaced with a combined
reference number, ISO/CIE 8995-1;
— scope revised;
— Annex A, Annex B, Annex C and Annex D added;
— editorially updated.
A list of all parts in the ISO/CIE 8995 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.

© ISO/CIE 2025 – All rights reserved
v
Introduction
Good lighting will create a visual environment that enables people to see, to move about safely and to
perform visual tasks efficiently, accurately, and safely without causing undue visual fatigue and discomfort.
The illumination can be provided by daylight, electric light sources, or a combination of both.
Good lighting requires equal attention to the quantity and quality of the lighting. While the provision of
sufficient illuminance on the task is necessary, in many instances the visibility depends on the way in which
the light is delivered, the colour characteristics of the light source and surfaces together with the level of
glare from the system. In this document, opportunity was taken to specify for various work places and task
types, not just the illuminance, but also the limiting of discomfort glare and minimum colour rendering
index of the source. Parameters to create comfortable visual conditions are proposed in the body of this
document. The recommended values are considered to represent a reasonable balance, having regard to the
requirements for safe, healthy, and efficient work performance. The values can be achieved with practical
energy efficient solutions.
There are also visual ergonomic parameters such as perceptual ability and the characteristics and attributes
of the task, which determine the quality of the operator’s visual skills, and hence performance levels. In
some cases, enhancement of these influencing factors can improve performance without the need to raise
illuminance. This can be achieved, for example by improving the contrast of the task attributes, enlarging
the task by the use of up to date visual aids (e.g. glasses) and by the provision of special lighting systems
with local directional lighting capability.
Adequate and appropriate lighting enables people to perform visual tasks efficiently and accurately
including tasks performed over a prolonged time period or of a repetitive nature. The degree of visibility
and comfort required in a wide range of work places is governed by the type and duration of the activity. The
lighting also affects circadian rhythms and mood as well as improving performance and well-being.
The final designed, installed and operated lighting system should provide efficient and effective good
quality lighting for the user needs tailored to their visual capacity, e.g. visual capacity of elderly users in
work places.
It is important that all clauses of this document are followed although the target values for lighting criteria
and specific requirements, depending of each type of task/activity, are tabulated in the schedule of lighting
requirements (see Clause 7).
This document reflects the generally recognized best practice at the time of publication.

© ISO/CIE 2025 – All rights reserved
vi
International Standard ISO/CIE 8995-1:2025(en)
Light and lighting — Lighting of work places —
Part 1:
Indoor
1 Scope
This document specifies lighting requirements for humans in indoor work places, which meet the needs for
visual comfort, performance and safety of people having normal, or corrected to normal visual capacity and
response to light.
This document specifies requirements for lighting solutions for typical indoor work places and their
associated areas in terms of quantity and quality of illumination. The illumination can be provided by
daylight, electric light sources, or a combination of both.
This document gives recommendations for good lighting to fulfil the needs of integrative lighting.
This document neither provides specific solutions nor recommendations for atmosphere or aesthetics
created by lighting. It does not restrict the designers' freedom from exploring new techniques nor restrict
the use of innovative equipment.
This document is not applicable for emergency lighting. For emergency lighting, see ISO 30061.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 3864-1, Graphical symbols — Safety colours and safety signs — Part 1: Design principles for safety signs and
safety markings
ISO 9680, Dentistry — Operating lights
ISO/CIE TS 22012, Light and lighting — Maintenance factor determination — Way of working
CIE S 017, ILV: International Lighting Vocabulary
CIE S 026, CIE System for Metrology of Optical Radiation for ipRGC-Influenced Responses to Light
CIE 58, Lighting for sports halls
CIE 62, Lighting for swimming pools
IEC 60601-2-41, Medical electrical equipment - Part 2-41: Particular requirements for the basic safety and
essential performance of surgical luminaires and luminaires for diagnosis
3 Terms and definitions
For the purposes of this document, the terms and definitions given in CIE S 017 and the following 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

© ISO/CIE 2025 – All rights reserved
— IEC Electropedia: available at https:// www .electropedia .org/
CIE maintains a terminology database for use in standardization at the following address:
— e-ILV: available at https:// cie .co .at/ e -ilv
3.1
activity area
partial area in the work place in which more than one visual task is carried out
Note 1 to entry: Visual tasks can be different in type and/or position.
Note 2 to entry: A room can contain one or more activity areas.
Note 3 to entry: The spatial orientation needs to be specified by the designer.
Note 4 to entry: An activity area is not to be considered as aggregation of a number of distinct task areas across a
larger area.
3.2
immediate surrounding area
zone of at least 0,5 m width surrounding the task area within the field of vision
3.3
background area
horizontal area at floor level adjacent to the immediate surrounding area (3.2) within the limits of space
3.4
work place
designated area in which work activities are carried out
4 Symbols and abbreviations
1)
Ē maintained average illuminance on walls
m,wall
1)
Ē maintained average illuminance on ceiling
m,ceiling
U illuminance uniformity
o
1)
Ē maintained average illuminance
m
α shielding angle
C-plane angle elevation angle
γ vertical photometric angle
DGP Daylight Glare Probability
L luminance
R CIE Unified Glare Rating (UGR)
UG
R R limit value
UGL UG
2)
Ē average cylindrical illuminance
c
1)
Ē maintained average cylindrical illuminance
m,c
1) According to CIE S 017, Ē is the value below which the average illuminance on a specified area shall not fall.
m
2) Approximated by the average of the four main directions

© ISO/CIE 2025 – All rights reserved
T correlated colour temperature
cp
R general colour rendering index
a
R special colour rendering index
i
TLM temporal light modulation
P IEC short-term light modulation/ temporal light modulation indicator
st,LM
SVM Stroboscopic Visibility Measure
DSE display screen equipment
f maintenance factor
m
Ē initial illuminance
i
maintained average luminance of the walls
L
m,wall
maintained average luminance of the ceiling
L
m,ceiling
ρ luminous reflectance of the wall
wall
ρ luminous reflectance of the ceiling
ceiling
5 Lighting design criteria
5.1 General
For good lighting practice, it is essential that, along with the required illuminances, additional qualitative
and quantitative needs are satisfied.
Lighting requirements are determined by the satisfaction of three basic human needs:
— visual performance, in which the workers are able to perform their visual tasks, even under difficult
circumstances and during longer periods;
— visual comfort, in which the workers experience physical and mental comfort; evidence shows that this
state contributes to improved work motivation, work quality, and reduced absenteeism;
— safety.
The principal parameters that describe the luminous environment with respect to daylighting and electric
lighting are:
— luminance distribution;
— illuminance and illuminance uniformity;
— glare;
— directionality of light;
— lighting in the interior space;
— colour rendering and colour appearance of the light;
— temporal light modulation.
© ISO/CIE 2025 – All rights reserved
These criteria are further detailed in Clause 5 and Clause 6, requirements and recommendations are given
in Clause 7.
NOTE In addition to the lighting, there are other visual ergonomic parameters which influence visual performance,
such as:
— the intrinsic task properties (size, shape, position, colour and reflectance properties of detail and background);
— normal visual capacity and response to light of the person (visual acuity, depth perception, colour perception) (see
CIE 227);
— for the visually impaired, for example those who are sensitive to glare or have visual field defects, adaptation and
decreased contrast and colour vision where dimming, protection against glare and colour rendering are especially
important factors to consider, see CIE 227.
5.2 Luminance distribution
5.2.1 General
The luminance distribution is a crucial factor to determine a proper luminous environment. It affects task
visibility and shall be properly controlled.
An appropriate adaptation luminance is needed to optimize:
— visual acuity (sharpness of vision);
— contrast sensitivity (discrimination of small relative luminance differences);
— efficiency of the ocular functions (such as accommodation, convergence, pupillary contraction, eye
movements, etc.).
The luminance distribution in the visual field also affects visual comfort. The following shall be avoided for
the reasons given:
— excessive luminances and luminance contrasts which can cause discomfort glare and reduced task
visibility;
— excessive luminance variation which can cause fatigue because of constant re-adaptation of the eyes.
Attention shall also be given to adaptation in moving from zone to zone within a building.
To create a well-balanced luminance distribution, the luminance values of all surfaces shall be taken into
consideration. They are determined by the reflectance and the illuminance on the surfaces. To avoid gloom
and to raise adaptation levels and comfort of people in buildings, it is highly desirable to have bright interior
surfaces. Room brightness is considered by specifying average illuminance values on walls and ceiling (see
Clause 7) and by recommending typical reflectance values (5.2.3).
The lighting designer shall consider and select the appropriate illuminance/luminance values for the interior
surfaces based on the guidance in 5.2.2, 5.2.3 and 5.2.4.
NOTE To simplify calculation procedures, this document does not consider the spectral reflectance values but
only the average reflectances of the surfaces themselves and considers these perfectly Lambertian surfaces, except for
the cases that deal with the surfaces with non-isotropic diffuse reflections.
5.2.2 Average luminance of surfaces
When isotropic diffuse reflection can be assumed, the luminance of a certain point on the surface is
proportional to the product of the illuminance on that point multiplied by the reflectance of the surface. That
means that the reflectance of and the illuminance on the surfaces is a simplified substitution of luminance
requirement.
NOTE 1 When the surfaces do not have isotropic diffuse reflection, the same luminous environment is not
necessarily assured from the different points of view even if it meets the illuminance requirements.

© ISO/CIE 2025 – All rights reserved
When calculating the luminance distribution by using lighting simulation programs, the lighting designer
shall consider and select the appropriate minimum requirements of the average luminance of the interior
surfaces based as below.
a) When isotropic diffuse reflection can be assumed.
— The lighting designer can set view positions for calculating luminance distribution anywhere.
b) When isotropic diffuse reflection cannot be assumed.
— The lighting designer shall choose several representative view positions in the space depending
on the tasks and/or activities being performed and calculate the average luminance values of walls
and ceiling from these positions. It is desirable to meet the minimum requirements for the average
luminance of walls and ceiling from all these positions.
The average luminance of walls and ceiling from all these positions depending on the tasks and/or activities
being performed in the space shall meet the minimum requirements. The minimum requirements for the
average luminance can be calculated from the recommended minimum illuminance (Clause 7) multiplied by
the recommended value of the reflectance in the wavelength between 380 nm to 780 nm for the calculation
purpose (see 5.2.3).
The average maintained luminance on the walls is calculated using Formula (1):
E ⋅ρ
mw, all wall
L = (1)
mw, all
π
where
Ē is the average maintained illuminance on the walls given in Table 9 to Table 62;
m,wall
ρ is the reflectance of the walls (see 5.2.3 for recommended reflectances in the wavelength
wall
between 380 nm to 780 nm for the calculation purpose).
The average maintained luminance of the ceilings is calculated using Formula (2):
ρ
E ⋅
ceiling
mc, eiling
L = (2)
mc, eiling
π
where
Ē is the average maintained illuminance on the ceilings given in Table 9 to Table 62;
m,ceiling
ρ is the reflectance of the ceilings (see 5.2.3 for recommended reflectances in the wavelength
ceiling
between 380 nm to 780 nm for the calculation purpose)
NOTE 2 The choice of view positions is at the discretion of the lighting designer, therefore, this method can be
considered as an auxiliary one in the lighting design process.
5.2.3 Reflectance of surfaces
For choice of materials and coatings, recommended diffuse reflectances in the wavelength between 380 nm
to 780 nm for the calculation purpose are:
— ceiling: 0,7 to 0,9;
— walls: 0,5 to 0,8;
— floor: 0,2 to 0,6.
© ISO/CIE 2025 – All rights reserved
The diffuse reflectance in the wavelength between 380 nm to 780 nm of major objects (such as furniture
and machinery) are normally in the range of 0,2 to 0,7.
NOTE Clear interior glass has a typical reflectance of 0,1.
5.2.4 Illuminance on surfaces
Illuminances on walls and ceiling together with surface reflectances (see 5.2.3) contribute to luminances
and are indicators for perceived room brightness.
Clause 7 provides minimum requirements for the maintained illuminance on walls (Ē ) and ceiling
m,wall
(Ē ) depending on the tasks and/or activities being performed in the space.
m,ceiling
NOTE Additional guidance can be found in Clause 6.
5.3 Illuminance
5.3.1 General
Areas to be lit are task areas and activity areas, the immediate surrounding area and background area,
walls, ceiling, and objects in the space.
The illuminance and its distribution on the task area and on its immediate surrounding area have a great
impact on how quickly, safely, and comfortably a person perceives and carries out the visual task.
All values of illuminances given in this document are maintained illuminances specified to fulfil visual
comfort and performance needs of people having normal or corrected to normal visual capacity and
response to light.
Designing for higher or lower illuminances in combination with controls allows the lighting installation
to be tailored to the specific context (i.e., differences in activities or personal characteristics). This can
be done using the context modifiers (see Table 1 and Table 2). Higher or lower illuminances shall be used
when relevant, e.g., only parts of the day. For calculation and measurement of illuminance averages and
uniformities, the grid specification in 5.5 shall be used.
5.3.2 Scale of illuminance
A factor of approximately 1,5 represents the smallest significant difference in subjective effect of illuminance.
In normal lighting conditions, approximately 20 lx of horizontal illuminance is required to just discern
features of the human face and is the lowest value taken for the scale of illuminances. The recommended
steps of illuminance (in lx) are given considering a perceptual difference.
20 - 30 - 50 - 75 - 100 - 150 - 200 - 300 - 500 - 750 - 1 000 - 1 500 - 2 000 - 3 000 - 5 000 - 7 500 - 10 000
5.3.3 Illuminances on the task area or activity area
The maintained illuminance value shall at least meet the requirement as given in Clause 7 (Ē ) and
m,required
shall take into account the following factors:
— psycho-physiological aspects, such as visual comfort and well-being;
— requirements for visual tasks;
— visual ergonomics;
— visual capabilities of the workers;
— practical experience;
— contribution to functional safety;

© ISO/CIE 2025 – All rights reserved
— economy.
The values given in Clause 7 are maintained illuminances evaluated over the task area or activity area on
the reference surface which can be horizontal, vertical or inclined.
However, it is required to increase the maintained illuminance (by one or two steps in the scale of illuminance
(see 5.3.2)), depending on the context modifiers given in Table 1 if the assumptions differ from the normal
visual conditions. The context modifiers apply when the actual conditions differ from the assumptions that
were made when defining the recommended values.
As an example, an increase of one step is recommended if one or two of the conditions listed in Table 1 apply
and an increase of two steps is recommended if more than two of these conditions apply. For examples, see
Annex C.
A modified value which considers common context modifiers is given in Clause 7 (Ē ). This modified
m,modified
value shall not be seen as an upper limit. It shall not be applied in the case where general lighting is used, in
which an entire space is uniformly lit without giving special consideration to individual visual tasks.
Table 1 — Context modifiers for increase of required maintained illuminance
visual work is critical;
errors are costly to rectify;
accuracy, higher productivity or increased concentration is of great importance;
task details are of unusually small size or low contrast;
the task is undertaken for an unusually long time;
the task area or activity area has a low daylight provision;
the visual capacity of the worker is reduced, e.g., due to age.
NOTE 1 When only general lighting is applied in a space, additional care is needed to ensure the lighting installation
can be still contextualized (see 6.2.4).
NOTE 2 Retinal illuminance declines with age due to reduced pupil size and increased spectral absorption of
the crystalline lens. It is reasonable for lighting practitioners to increase the illuminance in task area and not in
background area to compensate for the decrease in retinal illuminance in the elderly while avoiding intraocular light
scattering. More information can be found in CIE 227:2017.
NOTE 3 Daylight provision is considered in 6.5.
NOTE 4 For visually impaired people special requirements can be necessary with regard to illuminances and
contrasts.
The values of required Ē given in 7.3 are minimum values for normal working conditions.
m
Decreasing illuminance by one step may be considered when conditions from Table 2 apply.
Table 2 — Context modifiers for decrease of required maintained illuminance
task details are of an unusually large size or high contrast;
the task is undertaken for an unusually short time.
Dimming control may be used to achieve lower levels than Ē in Clause 7. Using dimming will
m,required
accommodate for possible future change in working conditions.
The size and position of the task area or the activity area shall be stated and documented by the lighting
designers in the designing documents, see Figure 1.
For work stations where the size and/or location of the task area or activity area(s) is/are unknown either:
— the whole area is treated as the task area;
— the whole area is uniformly (U ≥ 0,40) lit to an illuminance level specified by the designer.
o
© ISO/CIE 2025 – All rights reserved
If the task area becomes known, the lighting scheme shall be re-designed to provide the required or modified
illuminances.
If the type of the task is not known, then the designer has to make assumptions about the likely tasks and
state task requirements.
If the whole area is lit to a given illuminance value, then it is recommended that the lighting is controlled in
appropriate zones.
When multiple tasks take place in the area, requirements for all of these tasks shall be met. Usually this is
done by designing according to the task with the most onerous requirements.
This applies also to an activity area.
5.3.4 Illuminance on the immediate surrounding area
Large spatial variations in illuminance around the task area or activity area can lead to visual stress and
discomfort.
The illuminance on the immediate surrounding area shall be related to the illuminance on the task area or
activity area and shall provide a well-balanced luminance distribution in the visual field. The immediate
surrounding area is a band with a width of at least 0,5 m around the task area within the visual field.
The illuminance on the immediate surrounding area may be lower than the illuminance on the task area but
shall be not less than the values given in Table 3.
In addition to the illuminance on the task and activity area, the lighting shall provide adequate adaptation
luminance in accordance with 5.2.
The size and position of the immediate surrounding area shall be stated and documented by the lighting
designers in the designing documents.
Table 3 — Relationship of illuminances on immediate surrounding to the illuminance on the task
area or activity area
Illuminance on the task area or Illuminance on immediate sur-
activity area rounding areas
Ē lx
m
lx
≥ 750 500
500 300
300 200
200 150
≤ 150 equal to task area
5.3.5 Illuminance on the background area
In indoor work places, particularly those devoid of daylight, a large area outside the immediate surrounding
area needs to be illuminated. The background area shall be illuminated with a maintained illuminance of at
least 1/3 of the value of the immediate surrounding area. The background area shall be at least 3 m wide.
The size and position of the background area shall be stated and documented by the lighting designers in
the designing documents.
Figure 1 illustrates the minimum dimension of the background area in relation to task and immediate
surrounding area.
© ISO/CIE 2025 – All rights reserved
Key
task area or activity area (not true to scale) in a specified size and position (see 5.3.3)
immediate surrounding area (band with a width of at least 0,5 m around the task area or activity area
within the visual field)
background area (band with a width of at least 3 m adjacent to the immediate surrounding area or up to
the limits of the space for smaller rooms) horizontal on floor level
Figure 1 — Minimum dimensions of immediate surrounding area and background area in relation
to task area and activity area (figure is not true to scale)
5.3.6 Illuminance uniformity
In the task area or activity area, the illuminance uniformity (U ) shall be not less than the minimum
o
uniformity values given in the tables in 7.3.
Uniformity in the immediate surrounding area shall be U ≥ 0,40.
o
On the background area, the walls and the ceiling the uniformity shall be U ≥ 0,10.
o
These uniformities shall only be applied to the area illuminated either only by electric light sources or by the
combination of daylight and electric light sources.
Illuminance uniformities when daylight is available can be assured by adaptive lighting. Additional benefits
of daylight can compensate for the lack of uniformity. More information can be found in 6.5.
5.4 ipRGC-influenced responses to light – Melanopic Equivalent Daylight Illuminance
Light influences human health and well-being through its effects on the circadian system (which regulates, for
instance, sleep-wake behaviour) as well as by influencing perception and neuroendocrine, neurobehavioral
and cognitive functions. These effects can be strongly mediated by the intrinsically photosensitive retinal
ganglion cells (ipRGCs) and therefore the CIE has defined these as ipRGC-influenced responses to light (IIL
responses) [CIE S 026]. Appropriate stimulation of the ipRGCs is one of the aims of high-quality integrative
lighting. B.5.2 highlights several areas for which the evidence related to the effects of integrative lighting is
well established.
When setting targets for IIL effects (see ISO/CIE TR 21783 for more information and Annex B for practical
recommendations), all light and lighting quantities related to IIL effects shall be calculated in accordance

© ISO/CIE 2025 – All rights reserved
with CIE S 026 and employ the CIE standard illuminant D (daylight illuminant of ~6 500 K) as a reference
to compare to. In the context of this document the following quantities shall be used.
— The stimulation of the ipRGCs shall be quantified using the melanopic Equivalent Daylight Illuminance
(melanopic EDI or mel EDI, see CIE S 026).
— The melanopic efficacy of the luminous radiation from a light source or lighting installation, shall be
quantified using the melanopic Daylight Efficacy Ratio (melanopic DER or mel DER, see CIE S 026).
For a comprehensive evaluation of the effects of light on the circadian system, details shall be provided on,
for instance, the light exposure’s timing, duration, and observing field (for a typical user).
NOTE 1 Although some writers use the abbreviations M-EDI or M-DER to refer to melanopic EDI or melanopic DER,
this is ina
...