ISO/CIE TS 22012:2019

TECHNICAL ISO/CIE TS
SPECIFICATION 22012
First edition
2019-02
Light and lighting — Maintenance
factor determination — Way of
working
Reference number
©
ISO/CIE 2019
© ISO/CIE 2019
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Published in Switzerland
ii © ISO/CIE 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 3
5 Influencing factors . 4
5.1 Luminaire and/or light source characteristics. 4
5.2 Recoverable external factors . 4
5.3 Non-recoverable external factors . 4
5.4 Maintenance period, cleaning, replacement and surface refurbishment interval . 4
6 Maintenance factor determination . 5
6.1 Basic description of the method . 5
6.2 Luminous flux factor . 5
6.2.1 Luminous flux factor determination — General. 5
6.2.2 Luminous flux factor determination — Special case: Constant light output (CLO) 6
6.3 Survival factor . 8
6.3.1 Survival factor description . 8
6.3.2 Spot replacement regime . 8
6.3.3 Group replacement regime . 8
6.3.4 Regime combinations . 9
6.4 Luminaire maintenance factor . 9
6.4.1 Luminaire maintenance factor description . 9
6.4.2 Indoor luminaires .10
6.4.3 Outdoor luminaires .10
6.5 Surface maintenance factor .10
7 Use of the maintenance factor .10
7.1 Lighting design using the maintenance factor .10
7.2 Documentation .11
7.2.1 Documentation of maintenance factor determination .11
7.2.2 Documentation of maintenance schedules .11
7.3 Lighting verification using the maintenance factor .11
Annex A (informative) Maintenance factor determination examples .13
Annex B (informative) Luminous flux factor f tables (Typical examples) .17
LF
Annex C (informative) Luminaire maintenance factor f determination examples .19
LM
Annex D (informative) Surface maintenance factor f examples .24
SM
Bibliography .28
© ISO/CIE 2019 – All rights reserved 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
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.
ISO collaborates closely with the International Commission on Illumination (CIE) on all matters of
standardization for light and lighting.
This document was prepared by Technical Committee ISO/TC 274, Light and lighting. The document has
been jointly prepared with CIE JTC 11, Light and Lighting — Maintenance factor — Way of working.
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 © ISO/CIE 2019 – All rights reserved

Introduction
Continuous maintenance of lighting installations is essential as it ensures that the performance
of a system stays within the design limits and promotes safety and efficient use of energy. In the
design phase this is taken into account through the use of the maintenance factor. The maintenance
factor combines several different factors such as the assumed product/installation behaviour, the
environmental parameters and maintenance and cleaning schedules.
The methodology of determining the maintenance factor has been extensively documented by CIE
(see Clause 2 and bibliography). However, as the focus of these technical reports was predominantly
on incandescent and gas discharge light sources, more clarity is needed to ensure the proper use/
translation of the existing methodology towards technologies such as light emitting diodes (LED).
Technologies such as LED distinguish themselves from other technologies by their long lifetime, low
failure rate and their integration of components which were previously seen as separate components.
As such the previous methods used to determine the depreciation and survival of luminaires might
seem unusable and cause uncertainty. However, based on work by IEC (see Clause 2) the luminous flux
depreciation and light source failure parameters have now been (re)established for LED-based light
sources and allow for translation into an updated way of working to determine the maintenance factor
using the existing CIE methodology and data for luminaire and surface dirt depreciation.
This document combines insights from IEC standards with regard to product performance of luminaires
and light sources currently in the market with the existing determination methodology from CIE
Technical Reports. Furthermore, it references the data in the CIE Technical Reports with regard to the
impact of the environment on luminaires (accumulation of dirt on surfaces and luminaires).
This document provides the following:
— background information with respect to the principles of the maintenance factor and the relevant
parameters for indoor and outdoor applications;
— a detailed way of working on how to apply the maintenance factor determination method (as
described in CIE 154:2003 and CIE 097:2005) for outdoor and indoor lighting designs using the
technologies available in the market;
— explanation and examples on how to apply the maintenance factor and how to ensure proper
operation over time corresponding to the determined values.
© ISO/CIE 2019 – All rights reserved v

TECHNICAL SPECIFICATION ISO/CIE TS 22012:2019(E)
Light and lighting — Maintenance factor determination —
Way of working
1 Scope
This document specifies a standardized way of working for determining the maintenance factor for
both outdoor and indoor lighting installations using the methodology as described in CIE 154:2003 and
CIE 097:2005.
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.
CIE 097:2005, Maintenance of Indoor Electric Lighting Systems
CIE 154:2003, Maintenance of Outdoor Lighting Systems
CIE S 017, ILV International Lighting Vocabulary
IEC 62722-2-1, Luminaire performance — Part 2-1: Particular requirements for LED luminaires
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 terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
abrupt failure value
AFV
percentage of LED based products failing to operate at median useful life (L )
x
[SOURCE: IEC 62717:2014+AMD1: 2015, modified — generalized to products]
3.2
cleaning interval
planned time between cleaning of (parts of) the products and/or components
3.3
CLO lifetime
time over which the CLO (3.5) feature ensures a constant luminous flux
3.4
component replacement interval
planned time between replacement of one or more specified luminaire component(s)
© ISO/CIE 2019 – All rights reserved 1

3.5
CLO
constant light output
functionality to constantly adjust the luminous flux of the light source based on the known or predicted
depreciation behaviour of the light source to enable a constant luminous flux over time
3.6
failure probability
p
f
probability that the component (e.g. light source, luminaire) catastrophically fails
Note 1 to entry: Failure probability is expressed as a factor.
3.7
installation lifetime
time over which the installation is expected to function as designed
3.8
maintenance period
total time over which the maintenance is planned
Note 1 to entry: Within a single maintenance period different maintenance cycles can be planned for different
activities (e.g. cleaning, light source replacement).
Note 2 to entry: The maintenance period is often expressed in years.
3.9
median useful life
L
x
length of time until 50 % of a population of operating LED products reaches gradual light output
degradation of a percentage x
3.10
surface refurbishment interval
planned time between surface refurbishment instances where the reflecting properties of the room
or area surfaces are restored to their original state, including cleaning or painting of interior surfaces
such as walls and ceilings
Note 1 to entry: The concept ‘surface refurbishment interval’ does not refer to surfaces which are an integral
part of the luminaire.
3.11
survival probability
p
s
probability that a component continues to operate at a certain point in time
Note 1 to entry: Survival probability is expressed as a factor.
Note 2 to entry: The component can be e.g. a light source, a luminaire.
Note 3 to entry: There is a distinct difference between the survival factor (see 6.3) and the survival probability.
The survival probability describes the performance of an individual component whereas the survival factor
describes the outcome of the determination process as described in 6.3.
2 © ISO/CIE 2019 – All rights reserved

3.12
useful life
1)
L
x,By
length of time until a percentage y of a population of operating LED luminaires
reaches gradual light output degradation of a percentage x, expressed in general in the ‘L ’ format
x,By
Note 1 to entry: Useful life can be specified on different product levels such as on individual LED, LED module or
LED luminaire level. As for example luminaire design impacts thermal design, the useful life of the LED module
might be different from the useful life of the luminaire.
[SOURCE: IEC 62717:2014+AMD1: 2015, modified — specifier and quantity symbol
added to the term]
4 Symbols and units
The symbols and units in Table 1 apply.
Table 1 — Symbols and units
Symbol Term Unit
E measured illuminance lx
A
E corrected measured illuminance lx
A,c
E maintained illuminance lx
m
E initial illuminance lx
in
f luminous flux factor (see 6.2) 1
LF
f lamp luminous flux maintenance factor 1
LLM
f luminaire maintenance factor (see 6.4) 1
LM
f maintenance factor (see 6.1) 1
m
NOTE  In this document the term "maintenance factor" is used
for luminaires either with integrated or separate light sources, in
contrast to CIE 97 and CIE 154 where the light source is generally
seen as separate from the luminaire.
f survival factor (see 6.3) 1
S
f surface maintenance factor (see 6.5) 1
SM
Φ luminaire luminous flux lm
L
Φ CLO-corrected luminaire luminous flux lm
CLO
Φ standard luminaire luminous flux lm
S
Φ end-of-life luminaire luminous flux lm
e
Φ initial luminaire luminous flux lm
i
L median useful life (see 3.8) for x % remaining luminous flux h
x
L useful life h
x,By
p failure probability 1
f
p survival probability 1
s
1) Note that in the source IEC 62717 the expression "L B " is incorrectly presented as a quantity symbol for
x y
the term "useful life". As such, this document introduces the symbol L for the term “useful life” for use in this
x,By
document and further usage.
© ISO/CIE 2019 – All rights reserved 3

5 Influencing factors
5.1 Luminaire and/or light source characteristics
Depreciation of the luminaire and/or light source due to regular ageing and/or product-related
characteristics shall be taken into account. This includes the following components:
— luminous flux depreciation (either of the light source or the luminaire, depending on the luminaire
design) (see 6.2);
— light source and/or luminaire catastrophic failure (depending on luminaire design) (see 6.3).
5.2 Recoverable external factors
Recoverable factors concern those external factors, causing depreciation of the lighting installation
performance, of which the effects can be economically reversed or mitigated during service and/or
routine maintenance. The following factors shall be taken into account:
— removable pollution in/on the luminaire (see 6.4);
— depreciation of room or area surface characteristics relevant to the lighting installation (i.e.
reduction of reflectance due to degradation of walls or ceiling finishes) (see 6.5).
5.3 Non-recoverable external factors
Influencing external factors are classified as non-recoverable when they are caused by external
(environmental) factors and cannot be reversed during normal maintenance or are uneconomical
to restore. These factors include the ageing/fading of (non-replaceable) components due to the
environmental conditions and/or the irreversible soiling of components in applications due to specific
(aggressive) substances.
Although these factors should be taken into account during the design and maintenance planning phase,
they are not included in the maintenance factor as described in this document.
5.4 Maintenance period, cleaning, replacement and surface refurbishment interval
The choice of maintenance period, cleaning and replacement interval has a large impact on the
maintenance factor. Prior to determination of the maintenance factor, the following information shall
be determined:
— maintenance period (often expressed in years);
— cleaning interval of luminaires (often expressed in years);
— component replacement interval (often expressed in burning hours) and
— surface refurbishment interval (often expressed in years).
4 © ISO/CIE 2019 – All rights reserved

6 Maintenance factor determination
6.1 Basic description of the method
The maintenance factor f is determined using the Formula (1).
m
ff=⋅ ff⋅⋅ f (1)
m LF SLMSM
where
f is the luminous flux factor (see 6.2);
LF
f is the survival factor (see 6.3);
S
f is the luminaire maintenance factor (see 6.4);
LM
f is the surface maintenance factor (see 6.5).
SM
Annex A provides examples demonstrating the determination of these factors.
NOTE The methodology described in this document is a replacement of the methodology as described
in CIE 097:2005 and CIE 154:2003. Terminology has been changed to suit a more generalized approach for
luminaires either with integrated or separate light sources. Terminology changes are further specified in the
relevant paragraphs.
6.2 Luminous flux factor
6.2.1 Luminous flux factor determination — General
The luminous flux factor, f , expresses the depreciation of the luminous flux over time due to ageing of
LF
the light source or luminaire during regular operation (this excludes external factors). This is defined
as the ratio of depreciated luminous flux to the initial luminous flux.
For luminaires with an integrated light source the luminous flux factor, f , shall be determined for the
LF
(full) luminaire. For luminaires with a non-integrated light source the luminous flux factor, f , shall be
LF
determined for the light source (i.e. lamp).
NOTE 1 In CIE 097:2005 and CIE 154:2003 the equivalent of the luminous flux factor, f , is the lamp luminous
LF
flux maintenance factor ( f , abbreviation: LLMF). See Note in 6.1 for further information.
LLM
NOTE 2 The luminous flux factor, f , determined at luminaire level will better reflect reality as this includes
LF
all components and operating conditions. Therefore, this is the default method for all types of luminaires.
However, for luminaires with non-integrated light sources it is often not possible to determine this for the full
luminaire as data is only available for the light source and as such the luminous flux factor, f , on light source
LF
level is accepted for luminaires with non-integrated light sources.
For LED-based luminaires the luminous flux factor, f , shall be determined based upon the light source
LF
or luminaire replacement interval and shall be provided by the luminaire supplier according to the
definitions in IEC 62722-2-1.
The replacement interval can correspond to the median useful life, L . In this case the luminous flux
x
factor, f , equals x/100.
LF
EXAMPLE 1 L = 50 000 h translates to 80 % remaining luminous flux at 50 000 h. If the luminaire or light
source is also planned to be replaced at 50 000 h this would result in a luminous flux factor f = 0,80.
LF
© ISO/CIE 2019 – All rights reserved 5

If the replacement interval is different from the published values, the correct luminous flux factor, f ,
LF
needs to be supplied by the manufacturer. Alternatively, the tables with example values provided in
Annex B may be used as an approximation.
NOTE 3 In some cases the depreciation values are not individually stated, but can be obtained from the
lifetime values which will be presented as the median useful life, L , or the useful life ‘L ’ value. In both cases,
x x,By
only the x value of the L value is relevant for the luminous flux factor determination, the B element of ‘L ’ is
x y x,By
not taken into account in the f and consequently the f determination (e.g. the luminous flux factor f = 0,80
LF m LF
after 50 000 h for both L = 50 000 h and L = 50 000 h specifications).
80,B50 80,B10
NOTE 4 In some cases the depreciation values will be presented as ‘L F ’ values. The ‘L F ’ is a (no longer in
x y x y
use) indication of lifetime not just taking into account depreciation but takes into account multiple maintenance
factor parameters (namely luminous flux depreciation and survival factor). As such, this value is not appropriate
for the determination of the maintenance factor as it does not allow for separation of the luminous flux factor, f ,
LF
and the survival factor, f .
S
For light sources such as halogen lamps, high pressure sodium lamps, metal halide lamps or fluorescent
lamps, the depreciation of the luminous flux is often provided as a separate characteristic for given
lifetimes.
EXAMPLE 2 If the planned maintenance period is at 16 000 h and the rated lamp luminous flux maintenance
factor f provided by the manufacturer at 16 000 h is 0,90, then the luminous flux factor f is 0,90.
LLM LF
NOTE 5 Dimming and/or switching behaviour can have a positive or negative effect on the depreciation of the
light source, but this depends upon the luminaire and/or light source design. Information on these effects can be
requested from the manufacturer of the light source or luminaire.
6.2.2 Luminous flux factor determination — Special case: Constant light output (CLO)
Luminaires utilizing constant light output techniques constantly adjust the luminous flux based on the
known or predicted depreciation behaviour of the light source to enable a constant luminous flux over
time. This functionality needs to be captured in the determination of the luminous flux factor, f .
LF
The CLO feature is realized by initially dimming the light source to the predicted end-of-life luminous
flux and steadily increasing the current (and as such the power consumption) over time to compensate
for the depreciation in luminous flux due to ageing of the light source.
NOTE 1 The increasing power consumption over time also has an effect on the electrical design and energy
calculations for the installation but is also a factor when comparing different CLO and non-CLO luminaires.
NOTE 2 In the context of this TS, CLO refers to the stand-alone feature based on known or predicted
depreciation and does not include external input such as sensors. As such, it only applies to the luminous flux
factor, f . Other systems using external input to correct for depreciation exist but are not a part of this document.
LF
6 © ISO/CIE 2019 – All rights reserved

EXAMPLE
a) Standard, non-CLO luminaire behaviour b) CLO luminaire behaviour (simplified)
(simplified)
Key
1 Relative power
2 Relative luminous flux
X time in 1 000 h
Y relative output in %
A rated power and luminaire luminous flux for luminaires without CLO, 100 %
B end of useful life power for luminaires without CLO
C end of useful life luminous flux for luminaires without CLO (e.g. for L = 80 %)
D rated power and luminaire luminous flux for luminaires corrected for CLO (e.g. 80 % of maximum for L )
E end of useful life power for luminaires with CLO (100 %)
F end of useful life luminous flux for luminaires with CLO (e.g. 80 % of maximum for L )
Figure 1 — Illustration of CLO principle using simplified graph representations
Figure 1 a) shows a simplified representation of a standard product not using CLO, based on
L = 50 000 h (i.e. 20 % depreciation after 50 000 h). Both power and luminous flux are set to their
maximum value (point A). Over time, power remains the same (line between point A and B) whereas
the luminous flux for a luminaire without CLO depreciates to its end-of-life luminous flux (line between
point A and C, 80 % of luminous flux).
Figure 1 b) shows a simplified representation of the same luminaire as on left side, but with CLO
functionality. Both power and luminous flux start at 20 % below their maximum output at 0 h (based
on standard operation where total luminous flux depreciation is 20 % at the end of life - point D). Over
time, the luminous flux is kept constant (line between point D and F), by increasing the power (line
between point D and E). Note that at the end of life, both the standard and the CLO product have the
same power consumption (B versus E) and same luminous flux (C versus F).
Figure 1 illustrates the behaviour of a CLO luminaire during operation, however in practice, there are
two ways CLO luminaires specifications are provided by manufacturers. Depending on which of the
two options is used, the luminous flux factor, f , shall be determined differently. The current known
LF
options are:
1. the standard (non-CLO) specifications are specified (in which case the CLO correction needs to be
done in the maintenance factor using the luminous flux factor as specified below);
© ISO/CIE 2019 – All rights reserved 7

2. the corrected luminous flux is given (in which case no CLO correction is needed as this is already
represented in the corrected luminous flux, f = 1,00).
LF
For CLO luminaires, the luminous flux factor, f , shall be determined according to Formula (2).
LF
If ΦΦ==then f 10, 0
LCLO LF
(2)
Φ
e
If ΦΦ==then f
LR LF
Φ
R
where
Φ is the specified luminaire luminous flux;
L
Φ is the CLO-corrected rated luminaire luminous flux (i.e. Figure 1, point D);
CLO
Φ is the rated luminaire luminous flux (i.e. Figure 1, point A);
R
Φ is the end-of-life luminaire luminous flux (i.e. Figure 1, point C).
e
If the replacement interval is longer than the given CLO lifetime, the manufacturer shall be consulted
for the luminous flux factor, f , at the time of replacement.
LF
NOTE 3 Product specifications can include an indication of the CLO luminous flux, e.g. by specifying the dedicated
CLO luminous flux, or by specifying the lifetime including the CLO feature (examples of such indications are
L = 50 000 h or L = 50 000 h where either CLO or con (for constant) is added to the regular useful life
CLO 80 con 80
indications).
NOTE 4 In CLO installations light source behaviour and driver behaviour are interlinked. The calculations
assume that in the case of premature driver failure, the replaced components match the performance and
behaviour of the original part prior to failure.
6.3 Survival factor
6.3.1 Survival factor description
The survival factor, f , expresses the probability of the light source and/or luminaire to continue to
S
operate at a given time. This factor shall be based on the type of replacement regime (see 6.3.2, 6.3.3
and 6.3.4). In practice, the spot replacement regime is the default regime to ensure safety, however, this
needs to be validated for each project. If the survival factor, f , is based on the light source or luminaire
S
specifications, then the input parameters as used for the determination of the survival factor f , shall
S
match the input parameters as used to determine the luminous flux factor, f (e.g. if a specific number
LF
of burning hours was used to determine the luminous flux factor, f , the same number of burning hours
LF
shall be used for the survival factor, f , determination).
S
NOTE In CIE 097:2005 and CIE 154:2003 the equivalent of the survival factor, f , is the lamp survival factor
S
( f , abbreviation: LSF). See Note in 6.1 for further information.
LS
6.3.2 Spot replacement regime
The spot replacement regime assumes that when luminaires or light sources fail, they are immediately
replaced by a luminaire or light source with similar characteristics. In this case the corresponding
survival factor, f = 1,00.
S
NOTE In most cases there will be a slight delay in replacement of the failed luminaire or light source.
However, there are no internationally established methods to determine the impact of this delay.
6.3.3 Group replacement regime
For the group replacement regime, failure of all components that have a direct impact on the luminaire’s
ability to provide light shall be taken into account, with the exception of component failures already
8 © ISO/CIE 2019 – All rights reserved

accounted for in the luminous flux factor, f (e.g. failure of single LEDs as part of the regular luminous
LF
flux depreciation). The survival factor, f , shall be determined for the (relevant) component with the
S
shortest replacement interval. If multiple components have the same replacement interval, the survival
factor, f , will be determined based on the component with the lowest survival probability.
S
The survival factor, f , is calculated as according to Formula (3).
S
fp= (3)
ss
where
f is the survival factor;
s
p is the survival probability of the relevant component.
s
When a failure probability is given instead of the survival probability (e.g. the abrupt failure value AFV
for LED-based products or percentage of failures) the survival probability is calculated according to
Formula (4).
pp=−10, 0 (4)
sf
where
p is the survival probability;
s
p is the failure probability.
f
In case the failure probability is given in percentages, p shall be calculated by dividing the failure
f
probability percentage by 100.
If the survival probability of the driver and light source are given separately, then both are taken into
account using the above rules (e.g. if the driver has a shorter replacement interval than the light source,
the survival probability of the driver is used as the survival factor, f ).
S
If the survival probability is presented as a single probability for the full luminaire (without specifying
individual survival probabilities), then that survival probability is used to determine the survival
factor, f .
S
NOTE In general, the survival factor does not compensate for the light loss of a single luminaire.
6.3.4 Regime combinations
Combining the different maintenance regimes is quite common. In outdoor, the combination of spot and
group replacement is commonly used (e.g. luminaires are replaced on the spot, and after a specified
number of years the full installation is refurbished). As replacement of failed components is done
immediately, the spot replacement regime rules apply for determination of the survival factor, f .
S
6.4 Luminaire maintenance factor
6.4.1 Luminaire maintenance factor description
The luminaire maintenance factor, f (as also described in CIE 097:2005 and CIE 154:2003,
LM
abbreviation LMF) expresses the relative output of the luminaire due to dirt deposited on light sources,
optical components or other components influencing the luminaire output. The luminaire maintenance
factor, f , shall be based upon the luminaire characteristics and environmental conditions according
LM
to the procedure as described in CIE 097:2005 for indoor luminaires and CIE 154:2003 for outdoor
luminaires.
© ISO/CIE 2019 – All rights reserved 9

6.4.2 Indoor luminaires
The luminaire maintenance factor, f , for indoor luminaires shall be based upon the combination of
LM
the luminaire design, environmental pollution category and cleaning interval.
Example tables containing the classification of luminaire designs, applications and example luminaire
maintenance factors, f , based upon the cleaning interval can be found in C.1.
LM
For accurate data always consult the manufacturer.
6.4.3 Outdoor luminaires
The luminaire maintenance factor, f , for outdoor luminaires shall be based upon the combination of
LM
luminaire design (rated according to IP classification) and the environmental pollution category and
cleaning interval.
Example tables containing the classification of luminaire designs, environmental pollution category
and example luminaire maintenance factors, f , based upon the cleaning interval can be found in C.2.
LM
For accurate data always consult the manufacturer.
6.5 Surface maintenance factor
Depreciation of surface reflection shall be taken into account via the surface maintenance factor f .
SM
For indoor applications this relates to all relevant reflecting surfaces such as walls and ceilings whereas
for outdoor this only refers to tunnels and underpass applications (not included in this document, more
information on tunnels and underpasses can be found in CIE 088:2004). For outdoor lighting with the
exception of tunnels and underpasses the surface maintenance factor, f , is set to 1,00.
SM
NOTE 1 In CIE 097:2005 the equivalent of the surface maintenance factor, f , is the room surface maintenance
SM
factor ( f , abbreviation: RSMF). See Note in 6.1 for further information.
RSM
NOTE 2 When, for tunnels and underpasses the walls and/or ceilings are not taken into account in the lighting
design (i.e. reflections are not taken into account in the outcomes), the surface maintenance factor, f , is usually
SM
set to 1,00.
The indoor surface maintenance factor, f , (also called the room surface maintenance factor) shall
SM
be based on the principles as described in CIE 097:2005. This factor is based upon the luminaire
distribution, reflectance of the major surfaces (ceiling/wall/floor), the environmental pollution
category and the surface refurbishment interval.
Example tables for three different flux distributions, environmental pollution categories and reflectance
values can be found in Annex D.
NOTE 3 Another commonly used definition of surface maintenance factor is the ratio of room surface
reflectance at a given time to the initial reflectance value.
7 Use of the maintenance factor
7.1 Lighting design using the maintenance factor
The maintenance factor, f , shall be employed in lighting designs to ensure that the target requirements
m
are met throughout the agreed life of the installation when the installation is maintained according to
the defined maintenance schedule. The customer needs to be consulted to generate the required input
parameters.
Generally, the maintenance schedule is a balance between the cost of compensating for loss of
performance of the lighting installation compared with the cost of performing the maintenance
operation(s).
10 © ISO/CIE 2019 – All rights reserved

The maintained illuminance, E , shall be calculated according to Formula (5)
m
EE=⋅ f (5)
minm
or for luminance-based designs according to Formula (6).
LL=⋅ f (6)
minm
where
E is the maintained illuminance;
m
E is the initial illuminance;
in
L is the maintained luminance;
m
L is the initial luminance.
in
When luminaires of different types are used in the same installation, but the input parameters for
the maintenance factor vary significantly between luminaire types, the maintenance factor shall be
determined per luminaire type and implemented in lighting design accordingly.
7.2 Documentation
7.2.1 Documentation of maintenance factor determination
In combination with the determined maintenance factor, f , clear documentation shall be provided on
m
the conditions used to determine the maintenance factor, f .
m
This documentation shall include the individual factors that make up the maintenance factor, f
m
determination ( f , f , f , f ) and the key values used in determining these (such as the used lifetime)
LF S LM SM
and maintenance schedule.
7.2.2 Documentation of maintenance schedules
The maintenance schedule shall at least include the following information:
— installation lifetime;
— cleaning interval(s);
— component replacement interval(s);
— surface refurbishment interval.
7.3 Lighting verification using the maintenance factor
Illuminance (or luminance) measured by means of instruments at a given time represent the actual
state of the lighting system. A common objective of the measurement is to verify whether the lighting
system conforms to the target values set during the design phase.
To compare the measured value to the target-maintained illuminance value, E , it is necessary to
m
correct the measured value to represent the value as projected for the end of the installation life.
© ISO/CIE 2019 – All rights reserved 11

Formula (7) shall be used to calculate the corrected measured illuminance:
f
m
EE= . (7)
Ac, A
f
mI,
where
E is the corrected measured illuminance;
A,c
E is the actual measured illuminance
A
F is the interim maintenance factor reflecting the depreciation at the measurement time, calcu-
m,I
lated as if calculating a maintenance factor for the given time point;
f is the maintenance factor determined according to the end of life of the lighting system.
m
NOTE 1 The estimation of the interim maintenance factor using the regular maintenance factor determination
procedure as described in Clause 6 is a worst-case scenario assuming the full (negative) effects of luminaire and
surface depreciation for the cleaning cycles.
NOTE 2 The above procedure describes the basic principle. For more complex designs using separate
maintenance factors for different luminaire types, the above principle can be used in conjunction with lighting
simulations to determine the proper E .
A,c
12 © ISO/CIE 2019 – All rights reserved

Annex A
(informative)
Maintenance factor determination examples
A.1 Example 1: Parking area project 100 000 h, using spot replacement
Project information:
— Installation lifetime: 100 000 h;
— Burning hours per year: 4 000 h;
— Repair strategy: Spot replacement;
— Luminaire cleaning interval: 3 years;
— Pollution category: Low.
Luminaire information:
— Luminaire type: Flood lighting LED luminaire with integrated driver;
— Median useful life L : 100 000 h (no CLO);
— IP Class: IP66;
— Driver failure rate: 0,5 % per 5 000 h.
Determination:
1. Luminous flux factor: Installation lifetime is equal to the given median useful life at L . As such,
the luminous flux factor f =0,80;
LF
2. Survival factor: Project employs a spot replacement strategy. As such, the mentioned failure rate is
not relevant, the survival factor f = 1,00;
S
3. Luminaire maintenance factor: Based on Table C.5, an IP6X luminaire, with pollution category
"low", with a 3 years cleaning interval results in a luminaire maintenance factor f = 0,90;
LM
4. Surface maintenance factor: Only relevant for indoor installations and outdoor tunnels and
underpasses. Not applicable for this situation, f = 1,00.
SM
Maintenance factor f = 0,80 × 1,00 × 0,90 × 1,00 = 0,72.
m
A.2 Example 2: Urban street project 100 000 h, with CLO, using spot replacement
Project information:
— Installation lifetime: 100 000 h;
— Burning hours per year: 4 000 h;
— Repair strategy: Spot replacement;
— Luminaire cleaning interval: 3 years;
— Pollution category: Low.
© ISO/CIE 2019 – All rights reserved 13

Luminaire information:
— Luminaire type: LED luminaire with integrated CLO driver;
— Luminous flux: 6 000 lm non-CLO/4 800 lm CLO;
— Median useful life L : 100 000 h using CLO based on L ;
80 80
— Luminaire flux given as both non-CLO luminous flux (case A) and CLO luminous flux (case B);
— IP Class: IP66;
— Driver failure rate: 0,5 % per 5 000 h.
Determination:
1. Luminous flux factor: Installation lifetime is equal to the given median useful lifetime at L .
However, as this is a CLO luminaire, this warrants further investigation. Depending on how the
luminaire is specified, there are two options:
a) Luminous flux is specified as if no CLO is used. This means that the luminous flux depreciation
needs to be taken into account in the maintenance factor. As such: The installation lifetime is
similar to the given median useful life at L . As such, the luminous flux factor f = 0,80.
80 LF
b) Flux is specified
...