ISO/CIE 20086:2019

INTERNATIONAL ISO/CIE
STANDARD 20086
First edition
2019-01
Light and lighting — Energy
performance of lighting in buildings
Lumière et éclairage — Performance énergétique de l'éclairage des
bâtiments
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 .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviations . 2
4.1 Symbols . 2
4.2 Subscripts . 4
5 Description of the methods . 4
5.1 General . 4
5.2 Output of the method 1— Comprehensive method . 5
5.3 Optional methods . 5
5.3.1 Method 2 — Quick calculation method . 5
5.3.2 Method 3 — Direct metering method. 5
6 Method 1 — Calculation of the energy required for lighting . 6
6.1 Output data . 6
6.2 Calculation time steps . 6
6.3 Input data . 6
6.3.1 Lighting system data . . 6
6.3.2 Product data . . 7
6.3.3 System design data . . . 8
6.3.4 Operating conditions . 8
6.3.5 Constants and physical data. 8
6.4 Calculation procedure . 9
6.4.1 Applicable time step . 9
6.4.2 Operating conditions calculation . 9
6.4.3 Energy calculation . 9
6.5 Expenditure factors for lighting systems .13
7 Method 2 — Quick calculation of the energy required for lighting .16
7.1 Output data .16
7.2 Calculation time steps .16
7.3 Input data .17
7.3.1 Lighting system data . .17
7.3.2 Luminaire data .17
7.3.3 System design data . . .17
7.3.4 Operating conditions .17
7.3.5 Constants and physical data.17
7.4 Calculation procedure .17
7.4.1 Applicable time step .17
7.4.2 Operating conditions calculation .18
7.4.3 Energy calculation .18
7.5 Expenditure factors for lighting systems .20
8 Method 3 — Metered energy used for lighting .20
8.1 Output data .20
8.2 Calculation time steps .20
8.3 Input data .20
8.4 Calculation procedure of annual energy .20
9 Quality control .21
9.1 Method 1.21
9.2 Method 2.21
9.3 Method 3.21
© ISO/CIE 2019 – All rights reserved iii

10 Compliance check .22
10.1 General .22
10.2 Method 1.22
10.3 Method 2.22
10.4 Method 3.22
Annex A (informative) Input data sheet with default values and choices .23
Annex B (normative) Simplified method for installed power estimation .28
Annex C (normative) Assessment of the installed power for lighting systems in existing
buildings .31
Annex D (normative) Occupancy estimation .32
Annex E (informative) Expenditure factors for lighting systems .36
Annex F (normative) Constant illuminance .56
Bibliography .58
iv © ISO/CIE 2019 – All rights reserved

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 6, Energy performance of lighting in buildings.
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 2019 – All rights reserved v

Introduction
It is of paramount importance that correct lighting is provided in buildings. The convention and
procedures in this document assumes that the designed and installed lighting scheme conforms to
good lighting practices. For new and refurbished installations in the non-residential building sector the
design of the lighting system should conform to the requirements in the lighting applications standards
ISO 8995-1/CIE S 008 for indoor workplaces and ISO 30061/CIE S 020 for emergency escape lighting.
This document also assumes that the buildings can have access to daylight to provide all or some of the
illumination required in the rooms or zones and that in addition there will be an adequate amount of
electric lighting installed to provide the required illumination in the absence of daylight.
This document defines the methods for estimating or measuring the amount of energy required or used
for lighting in buildings. The method of separate metering of the energy used for lighting will also give
regular feedback on the effectiveness of the lighting control.
The methodology of energy estimation not only provides values for the Lighting Energy Numeric
Indicator (LENI) but it will also provide input for the heating and cooling load estimations for the
combined total energy performance of building indicator.
Figure 1 gives an overview of the methodology and the flow of the processes involved.
NOTE The dotted line linking preliminary annual LENI to the comprehensive method indicates the required
follow-up of the budget calculation with the comprehensive calculation during the detailed lighting design
process.
Figure 1 — Flow chart illustrating alternative routes to determine energy use
vi © ISO/CIE 2019 – All rights reserved

INTERNATIONAL STANDARD ISO/CIE 20086:2019(E)
Light and lighting — Energy performance of lighting in
buildings
1 Scope
This document specifies the methodology for evaluating the energy performance of lighting systems
for providing general illumination inside non-residential buildings and for calculating or measuring the
amount of energy required or used for lighting inside buildings.
This document does not cover lighting requirements, the design of lighting systems, the planning of
lighting installations, the characteristics of lighting equipment (lamps, control gear and luminaires)
and systems used for display lighting, desk lighting or luminaires built into furniture. This document
does not provide any procedure for the dynamic simulation of lighting scene setting.
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 8995-1/CIE S 008, Lighting of work places — Part 1: Indoor
ISO 10916, Calculation of the impact of daylight utilization on the net and final energy demand for lighting
ISO 30061/CIE S 020, Emergency lighting
IEC 60598 (all parts), Luminaires
CIE S 017, ILV, International Lighting Vocabulary
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
time step
t
s
period in which the energy is evaluated
Note 1 to entry: Measured in hour, month, year.
3.2
standby energy
energy required for charging batteries and/or the energy required for lighting controls during the time
the electric lights are switched off
Note 1 to entry: Lighting controls and emergency battery charging circuits are only considered where power is
supplied via a luminaire.
© ISO/CIE 2019 – All rights reserved 1

3.3
lighting control
device connected to the luminaire to vary the light output
Note 1 to entry: In this document lighting controls are only considered where power is supplied via a luminaire.
3.4
lighting system
set of light sources and/or lamps with luminaires and related equipment, if any, interacting together to
satisfy lighting application requirements
Note 1 to entry: The lighting system can be dedicated to:
a) the support of (a) specified visual task(s) under specified conditions considering other requirements such as
human comfort, safety, the appearance of the surrounding environment and energy consumption;
b) the support of other than human tasks, such as plant growth or breeding of animals.
Note 2 to entry: The lighting system can include physical components, communication protocols, user interfaces,
software and networks to provide control and monitoring functions.
[SOURCE: CIE DIS 017:2016; Term 17-29-029]
3.5
expenditure factor
expense factor
effort factor
indicator of the energy efficiency of a given lighting system compared to a reference system
4 Symbols and abbreviations
4.1 Symbols
For the purposes of this document, the specific symbols listed in Table 1 apply.
Table 1 — Symbols and units
Symbol Name of quantity Unit
A Total useful area m
A Partial area which is lit by daylight m
D
A Area not lit by daylight m
ND
A Sum of task areas within the room m
s
D Daylight factor %
D Daylight availability classification 1
class
e Expenditure factor for lighting systems 1
L
e Partial expenditure factor for constant illuminance control 1
L,C
e Partial expenditure factor for daylight dependant lighting control 1
L,D
e Partial expenditure factor for the electric lighting system 1
L,ES
e Partial expenditure factor for delivery of electric light 1
L,ES,del
e Partial expenditure factor for distribution of electric light 1
L,ES,dis
e Partial expenditure factor for generation of electric light 1
L,ES,gen
e Partial expenditure factor for occupancy dependant lighting control 1
L,O
E Maintained illuminance lx
m
E Maintained illuminance on immediate surround of task area lx
sur
E Maintained illuminance on the task area lx
task
2 © ISO/CIE 2019 – All rights reserved

Table 1 (continued)
Symbol Name of quantity Unit
F Absence factor 1
A
f Factor for the efficiency of the operating device 1
B
F Constant illuminance factor 1
c
F Factor for reduced power of area 1
CA
F Factor for the efficiency of the constant illuminance control 1
cc
F Daylight dependency factor 1
D
F Lighting control factor 1
D,C
F Daylight supply factor 1
D,S
F Factor for light source efficiency 1
L
f Maintenance factor 1
m
F Correction factor for maintenance factor 1
CMF
F Occupancy dependency factor 1
o
F Controls function factor 1
oc
F Utilization factor of the luminaire 1
u
F Utilization factor for determination of the energy use 1
u,e
h Mounting height of luminaire m
m
K Room Index 1
time period at which x % of the measured initial luminous flux value
L h
x
is maintained
L Length of room m
R
N Number of days in month i d
i
n Number of lamps in the luminaire 1
La
P Installed electric power density W/m
p Specific electrical evaluation power W/(m lx)
P Control standby power of luminaire i W
c,i
P Electrical evaluation power density for determination of the energy use W/m
e
P Total emergency standby power W
em
P Emergency charging power of luminaire i W
e,i
P Power of luminaire i W
i
P Power density of area j W/m
j
P Illuminance-normalized power density of area j W/(m lx)
j,lx
P Total power of n luminaires W
n
P Total controls standby power W
pc
P Lamp rated power W
r
Q Lighting energy numeric indicator (LENI) for a building kWh/m
LENI
Q Lighting energy numeric indicator for an area or relevant zone kWh/m
LENI,sub
R General colour rendering index 1
a
t Daylight time h
D
t Daylight absence time h
N
t Time step hour, month, year
s
t Total operating hours h
tot
t Number of hours in a standard year h
y
W Total annual energy used for lighting kWh
W Annual energy required for lighting for an area or a zone kWh
az
© ISO/CIE 2019 – All rights reserved 3

Table 1 (continued)
Symbol Name of quantity Unit
W Total energy for illumination kWh
L,t
W Metered energy kWh
mt
W Total energy for standby kWh
P,t
w Width of room m
R
W Energy per time step kWh
t
W Energy used for lighting Wh
us
W Energy needed for lighting Wh
nd
Standby energy density for automatic lighting controls of the luminaire
W kWh/m
pc
per year
Standby energy density for battery charging of emergency luminaires
W kWh/m
pe
per year
η Luminaire luminous efficacy lm/W
L
η Luminaire light output ratio 1
LB
η Utilance 1
R
4.2 Subscripts
For the purposes of this document, the specific subscripts listed in Table 2 apply.
Table 2 — Subscripts
i Relevant element under consideration
or
Month number, 1 – 12
j Relevant area under consideration
5 Description of the methods
5.1 General
This document covers three methods for the assessment of the energy required for electric lighting
within a building, either by calculation (method 1 and method 2) or by direct metering of the lighting
circuit (method 3). The calculation method 1 offers two options,
1) for new or refurbished buildings, and
2) for existing buildings.
For new and refurbished buildings it also offers a quick calculation method 2 for the annual energy
estimation.
This document offers calculation methods, with different levels of accuracy for the installed power,
occupancy estimation and daylight availability.
Method 1 provides the most accurate calculation procedure and it relies upon a comprehensive lighting
scheme design as the main input to the energy calculation.
Method 2 provides a quick estimation aimed for pre-design calculations and employs default values.
Default values are provided in Annex A.
4 © ISO/CIE 2019 – All rights reserved

Method 3 provides the most accurate energy use for lighting information but can only be used after
the building has been commissioned and occupied. This method can also be linked to the Building
Management System (BMS) of the building to provide continuous smart metering.
5.2 Output of the method 1— Comprehensive method
This method covers the calculation of the energy requirements of lighting systems in non-residential
buildings where a comprehensive lighting system design has been performed. This calculation method
is suitable for use during the design of new or refurbished buildings and for assessing existing buildings.
The method output shall be in terms of kilowatt hours per time step for the building. The output value
shall be normalized for the considered time step to square meters of the useful area to give the sub-
LENI value. If the time-step is yearly this is the Lighting Energy Numeric Indicator LENI.
The time step of the output can be:
— yearly,
— monthly, or
— hourly,
in accordance with the time step of the input data.
5.3 Optional methods
5.3.1 Method 2 — Quick calculation method
This method covers the calculation of the energy requirements of lighting systems for non-residential
buildings where a comprehensive lighting system design has not been performed. The method makes
use of quick calculation and default data and the result gives budget values.
The method output shall be in terms of kilowatt hours per year for the building. This yearly output
value shall be normalized to square meters of the useful area to give the LENI.
The time step of the output shall be yearly.
This method is suitable for use during the conceptual stage of design of new or refurbished buildings.
5.3.2 Method 3 — Direct metering method
This method covers the direct measurement of the energy used by lighting system in non-residential
buildings by segregated direct metering. This method gives the true value of energy used by the lighting
system and can be used to verify the values obtained by the calculation methods.
The method output shall be in terms of kilowatt hours per time step for the building. The yearly output
value shall be normalized to square meters of the useful area to give the LENI.
The time step of the output can be:
— yearly,
— monthly, or
— hourly,
in accordance with the time step of the input data.
This method is suitable for use in existing buildings where the lighting circuit is sufficiently segregated
to allow separate metering.
© ISO/CIE 2019 – All rights reserved 5

This method is applicable to buildings with facilities for separate metering of the electricity used for all
lighting within the building. The metering can alternatively be by the BMS arrangement.
The calculated or measured annual energy required for lighting can be normalized to a unit area to
generate the LENI. LENI provides a comparable measure of the energy performance of the lighting
installation in the buildings. When the output value is obtained for other time steps it shall be
normalised to the unit area to give the sub-LENI value.
6 Method 1 — Calculation of the energy required for lighting
6.1 Output data
The output data of this method are listed in Table 3.
Table 3 — Output data of this method
Description Symbol Unit
Specified time step, e.g. hourly, monthly or
t hour, month, year
s
annually
Energy used for lighting (in kWh) per time
step (e.g. hourly, monthly or annually) within W kWh
t
rooms or zones
LENI is the area normalized annual energy used for lighting within the building [kWh/m ]. LENI
produced by method 1 provides the most accurate calculated Q .
LENI
6.2 Calculation time steps
The methods described in clause 6 are suitable for the following calculation time steps:
— Yearly – Taken as 8 760 h;
— Monthly – Taken as an average of 730 h;
— Hourly – 1 h derived from monthly calculated value divided by 730.
NOTE If more accurate data for occupancy and daylight is available for hourly intervals this data can be used.
6.3 Input data
6.3.1 Lighting system data
For the comprehensive calculation method the energy estimation shall be based upon the electric
lighting system that provides illumination in accordance with the requirements for non-residential
buildings of ISO 8995-1/CIE S 008 for lighting of indoor work places and requirements for emergency
lighting according to ISO 30061/CIE S 020.
It is important that for all buildings the lighting solution shall combine daylight, if available, and electric
light to fulfil all requirements in accordance with ISO 8995-1/CIE S 008 and the general and specific
lighting criteria for the places within the buildings.
6.3.1.1 New or refurbished building lighting system
The lighting scheme design process of the electric lighting system for all rooms and zones within the
building shall deliver as output the required type and number of luminaires and these shall be listed in
the product schedule.
NOTE 1 The comprehensive lighting system design process is not part of this document.
6 © ISO/CIE 2019 – All rights reserved

The lighting system design shall give the following input data and details for each room and zone of the
building:
— the types of luminaires, identified by a unique product reference code;
— the quantities of each specific type of luminaire;
— the control technique and device types;
— the maintenance factor ( f ) assumed in the design.
m
NOTE 2 The specific type of the luminaire includes information on the product as well as the lamp and ballast
combination if applicable.
All luminaires listed for use shall comply with the requirements specified in IEC 60598 (all parts).
6.3.1.2 Existing building lighting system
The lighting system shall be surveyed to give the following input data and details for each room and
zone of the building:
— the types of luminaires, identified by a unique product reference code;
— the quantities of each specific type of luminaire;
— the control technique and device types;
— the maintenance factor ( f ) defined by the maintenance schedule.
m
6.3.2 Product data
6.3.2.1 General
Where the comprehensive method is being used, the data in Table 4 to 7 shall be specified for each
product type given in the product schedule:
Table 4 — Luminaire identification
Code Description
Table 5 — Power of luminaire i (P )
i
Power
Code
W
Table 6 — Control standby power of luminaire i (P )
c,i
Power
Code
W
Table 7 — Emergency charging power of luminaire i (P )
e,i
Power
Code
W
© ISO/CIE 2019 – All rights reserved 7

In the case of existing buildings where the luminaire data is not available from the manufacturer the
method described in Annex C shall be used for obtaining the value of the maximum luminaire power.
NOTE In this document product means light sources and/or lighting controls and/or emergency battery
charging circuits where power is supplied via a luminaire.
6.3.2.2 Luminaire description data (qualitative)
The product description data shall indicate the product characteristics and state the functional
capabilities regarding dimming control, integral detectors and emergency lighting facility.
6.3.2.3 Luminaire technical data
The luminaire technical data, in accordance with Table 4 to 7, shall be the values declared by the
manufacturer in accordance with the certified measurements that are performed in accordance with
the relevant product standards. If standby energy density values declared by the manufacturer are not
available, then default values are given in Table A.1 for information.
Declared values are given at standard reference test conditions. Declared values shall be adjusted in
accordance with the actual operating conditions. This adjustment is part of the calculation procedure.
This applies both to standard test values and to field test measurements.
6.3.3 System design data
Calculations shall be made for each area of a zone or building to establish the installed lighting power,
P , P and P , and to estimate the impact of occupancy, daylight and over design/maintenance factors
n em pc
on the lighting controls by determining the values of the dependency factors, F , F and F . These shall
o D c
be presented as shown in Table 8.
Table 8 — System design data
Area Code F F F P P P
o D c n em pc
6.3.4 Operating conditions
The operating conditions for the lighting system are specified in the design of the lighting system
to fulfil the lighting requirements for the tasks or activity in a zone or building. The electric lighting
system shall be designed to meet all the relevant lighting criteria and the system shall be managed by
controls. The controls shall be manually or automatically operated. Details of control types and their
operation and effectiveness are given in CEN/TR 15193-2.
In addition the occupancy and activity patterns shall be defined to allow the evaluation of t and t for
D N
each area of a zone or building. These shall be presented as shown in Table 9.
Table 9 — Times for operating conditions
Area Code t t
D N
6.3.5 Constants and physical data
Number of hours in a standard year (t ) – defined as 8 760 h.
y
8 © ISO/CIE 2019 – All rights reserved

6.4 Calculation procedure
6.4.1 Applicable time step
This procedure can be used with the following time steps:
— yearly,
— monthly, or
— hourly.
NOTE No dynamic effects are explicitly taken into account because there are no significant time constants.
This procedure is not suitable for dynamic simulations.
6.4.2 Operating conditions calculation
If no better values are available the default values of t , and t as provided in Table A.2 and F as
D N A
provided in Table A.6 shall be used.
The occupancy schedule shall be provided based on documented assumptions.
NOTE Examples are provided in ISO 18523-1 and other national or regional references.
6.4.3 Energy calculation
6.4.3.1 General
The lighting energy calculation method is shown in Figure 2. The procedure represents the principle of
the method and needs to be applied for different areas/zones.
© ISO/CIE 2019 – All rights reserved 9

Figure 2 — Flow chart illustrating the calculation of energy for lighting by method 1
6.4.3.2 Installed power calculation
The power P of luminaire i [W], shall be the declared circuit power of the luminaire when operating at
i
maximum power. The value of P shall include the power supplied to operate all lamp(s), ballast(s) and
i
other component(s) when operating at maximum power.
The required connected or installed power for the lighting system shall be calculated by summation
of the power requirements of the specified luminaires in the lighting scheme within each area of the
building by using Formula (1):
in=
PP= W (1)
n i  
∑
i=1
where n is the number of individual luminaires in the area defined in the lighting system design.
Where available accurate data from installed lighting should be used.
10 © ISO/CIE 2019 – All rights reserved

6.4.3.2.1 Assessment of installed power in existing buildings
The assessment of the installed power for the lighting system in existing buildings shall be made by
the procedure described in Annex C. The installed power for the lighting system shall be calculated by
working out the power supplied to the luminaires within each area of the building by using Formula (1).
6.4.3.3 Standby system power requirements
The required total installed power to charge the batteries in emergency luminaires P and to provide
em
standby power for the automatic controls in the luminaires when the lamps are not operated P shall
pc
be calculated and shall be made by summing the standby power P for charging the batteries and
e,i
the standby power P for the automatic control for each specified luminaire within each area of the
c,i
building by Formulae (2) and (3):
in=
PP= W (2)
 
em e,i  
∑
i=1
in=
PP= W (3)
pc ∑ c,i  
i=1
where n is the number of individual luminaires in the area defined in the lighting system design.
Details of the standby power and energy calculation and requirements are provided in 6.4.3.7.
6.4.3.4 Occupancy dependency factor F
o
6.4.3.4.1 General
The occupancy dependency factor F shall be calculated by the process shown below.
o
6.4.3.4.2 Case F = 1
o
F shall be taken to equal 1,0 when:
o
— the lighting is switched on 'centrally', i.e. in more than one area at once (e.g. a single automatic
system – for instance with timer or manual switch for an entire building, or for an entire floor, or for
all corridors etc.). This applies regardless of the type of 'off-switch' (automatic or manual, central or
per room etc.);
— multi-occupancy or traffic areas larger than 30 m are illuminated by a group of luminaires that are
(manually or automatically) switched together.
6.4.3.4.3 Case F < 1
o
F shall be taken as less than 1,0:
o
— in meeting rooms or zones (whatever the area size covered by one switch and/or by one detector),
as long as they are not switched on 'centrally', i.e. together with luminaires in other rooms or zones;
— in other rooms or zones where F is not deemed to be equal to 1,0. In the case of systems with
o
automatic presence and/or absence detection the area covered by the detector should closely
correspond to the area illuminated by the luminaires that are controlled by that detector.
In these instances, F shall be determined according to the value of F as follows in Formulae (4) to (6):
o A
 
0,0 ≤ F < 0,2   FF=−11−⋅F /,02 (4)
A ()
oocA
 
© ISO/CIE 2019 – All rights reserved 11

0,2 ≤ F ≤ 0,9   FF=+02, − F (5)
A
oocA
 
0,9 ≤ F ≤ 1,0   FF=−7101⋅⋅ F − (6)
() ()
A
oocA
 
where
F is the proportion of the time that the space is unoccupied;
A
F is determined as a function of the lighting control system.
oc
Details of the estimation of F , F and F are given in Annex D.
o A oc
6.4.3.5 Daylight dependency factor F
D
The daylight dependency factor F shall be calculated for a room or zone in the building as a function
D
of the daylight supply factor F and the daylight dependent electric lighting control factor F by
D,S D,C
Formula (7):
FF=−1 ⋅F (7)
()
DD,S D,C
The method for the determination of the daylight supply factor F and the daylight dependent electric
D,S
lighting control factor F are given in ISO 10916.
D,C
6.4.3.6 Constant illuminance dependency factor F
c
The constant illuminance dependency factor F shall be taken as the ratio of the average input power at
c
a specified time to the initial installed input power to the luminaire. The specified time shall be taken
to be the period specified in the maintenance schedule for one complete maintenance cycle.
The constant illuminance dependency factor F shall be calculated by Formula (8):
c
FF=−1 1− f (8)
()
cccm
where
F is the efficiency factor of the constant illuminance control;
cc
f is the maintenance factor for the scheme.
m
For technologies with inbuilt constant light output capabilities used in systems without constant
illuminance sensing the F value shall be based on the method according to Annex F.
c
12 © ISO/CIE 2019 – All rights reserved

6.4.3.7 Calculation of energy for lighting
The total estimated energy required for lighting for a period in a room or zone of the building shall be
estimated by using Formula (9):
WW=+W kWh (9)
tL,t P,t  
Where W is the estimated lighting energy required to fulfil the illumination function in a room or
L,t
zone of the building, it shall be established using Formula (10):
 
WP=⋅FF⋅⋅tF +t 1000 kWh (10)
() ()
{}
L,tc∑ n oD DN  
 
Where W is the estimated standby energy required during non-lighting periods to provide charging
P,t
energy for emergency lighting and the activation energy for lighting controls in a room or zone of the
building, it shall be established using Formula (11):
WP=⋅tP+⋅t 1000 kWh (11)
() ()
{}
P,tp∑ cs em e  
NOTE 1 The total lighting energy can be estimated for any required time step period t (hourly, monthly or
s
yearly) in accordance with the time interval of the dependency factors used.
NOTE 2 This estimation does not include the power consumed by control systems remote from the luminaire
and not drawing power from the luminaire.
The annual energy for electric lighting within a building shall be calculated using Formula (12):
Wt=⋅8760/ W kWh (12)
st∑  
summed across all rooms and zones within the building.
Q for the building shall be established using Formula (13):
LENI
 
QW= /A kWh/m (13)
LENI
 
where
W is the total annual energy used for lighting [kWh];
A is the total useful floor area of the building [m ].
6.5 Expenditure factors for lighting systems
This methodology allows a quick analysis of the energy flows in an electric lighting system.
The expression of energy performance of a given lighting system can be indicated by the expenditure
factor, where the higher the expenditure factor the less efficient is the lighting system. It does not affect
the determination of the energy required for lighting. Instead it can be derived by correlation of the
previously derived values. Applying this methodology allows a quick analysis of the energy flows in
an electric lighting system, separately for each of its technical components. As specific conventions
are required for the energy assessment of lighting systems, such as luminous efficacy and luminous
intensity distribution, the absolute values received for the expenditure factor are specific for lighting
and cannot be directly compared with other technical building services.
© ISO/CIE 2019 – All rights reserved 13

The expenditure factor for lighting systems is defined according to Formula (14):
W
us
e = (14)
L
W
nd
where
e is the expenditure factor for lighting systems;
L
W is the energy used for lighting (either calculated or measured);
us
W is the reference energy needed for lighting.
nd
It can be derived by the following formal separation of the individual influences ac
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