Position Statement on UV Germicidal Irradiation

GUIDELINES FOR QUANTIFICATION OF AIRBORNE
PATHOGEN INACTIVATION BY UVGI TECHNOLOGIES

February 2022

© Global Lighting Association 2022

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FOREWORD
About the Global Lighting Association
The Global Lighting Association (GLA) is the voice of the lighting industry on a global basis. GLA
shares information on political, scientific, business, social and environmental issues of relevance tothe lighting industry and advocates the position of the global lighting industry to relevant
stakeholders in the international sphere. See www.globallightingassociation.org.
UV-C and urgent need for quantification guidelines
Ultraviolet germicidal irradiation (UVGI) air disinfection technology is an established method to
reduce infection risks caused by a wide range of contagious airborne diseases. However it does raise
the following questions: 1. Does it work? and 2. Is it safe?
The Global Lighting Association answered the safety question with its 2020 publication UV-C Safety
Guidelines (reproduced by the International Electrotechnical Commission in IEC PAS 63313), whichconcludes that the technology is safe if installed correctly. GLA has reconvened the same technicaltask force to prepare this statement with guidelines for the quantification of airborne pathogen
reduction by UVGI technologies.

© Global Lighting Association 2022

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TABLE OF CONTENTSFOREWORD2

1. INTRODUCTION

4

2. SCOPE OF THIS GUIDANCE DOCUMENT

5

3. EXAMPLES OF UVGI OPERATING PRINCIPLES

6

3.1 No disinfection measures

6

3.2 UVGI air cleaners

6

3.3 UVGI luminaires

7

4. QUANTIFICATION OF MICROBIAL CLEANING CAPABILITIES OF UVGI PRODUCTS
IN A TEST CHAMBER

8

5. QUANTIFICATION OF MICROBIAL CLEANING CAPABILITIES OF UVGI PRODUCTS
IN A REAL APPLICATION

8

5.1

Reduction mechanism for active airborne pathogens in a room and their genericquantification

9

5.2

Recommended ventilation rates

12

5.3

UVGI air cleaner - relationship between required UVGI equivalent ventilation
rate in the application and CADRsurrogate-pathogen

12

UVGI luminaire - relationship between required UVGI equivalent ventilation
rate in the application and eqCADRsurrogate-pathogen

13

5.4

6. TERMS AND DEFINITIONS

15

7. REFERENCES

16

ANNEX

17

© Global Lighting Association 2022

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1. INTRODUCTION
Pathogens spread by touch (direct person-to-person or indirect via surface transfer), spray (ballistic
droplets) and inhalation of airborne aerosols are causing diseases such as SARS-CoV-2. The spread of
pathogens by touch and the transmission of droplets can be reduced by surface cleaning including
washing hands, use of personal protective equipment (PPE) such as mouth masks and appropriate
behaviours such as social distancing. The spread and inhalation of pathogens by aerosols can be
reduced by use of medical PPE and/or air cleaning. Air cleaning can be achieved by air replacement
utilising ventilation (either natural and/or mechanical) and/or air disinfection technologies such as
Ultraviolet Germicidal Irradiation (UVGI) and ionisation.
UVGI air disinfection technology is an established method to reduce infection risks caused by a wide
range of highly contagious airborne diseases. During the last 80 years, the capability of UVGItechnology to inactivate pathogens responsible for airborne diseases such as measles, influenza andtuberculosis has been proven over and over again, as shown in studies by Wells [1] and McLean [2]which identified 74% and 90% transmission reduction in these diseases respectively. It follows thatUVGI technology is also one of the key tools to reduce the level of indoor air contamination [3] andthereby contribute to improving human health in general, including during and beyond the current
COVID-19 pandemic. The corresponding fundamental pathogen inactivation theory andmathematical modelling are well established and described in existing UVGI documentation.
Section 2 describes the scope of this guidance document and Section 3 illustrates the UVGI working
principles of the products in scope. In Section 4, the Global Lighting Association endorses thestandardisation of a microbial clean air delivery rate which can be determined in a defined test
chamber, and which is an unambiguous UVGI product specification. In Section 5 it is explained how
these UVGI product specifications can be used to quantify the microbial cleaning capabilities of the
UVGI products in a real application/room.
The Global Lighting Association recommends this document for use as reference material byinternational standards development organisations such the International ElectrotechnicalCommission (IEC) and the International Organization for Standardization (ISO).

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2. SCOPE OF THIS GUIDANCE DOCUMENT
This document describes quantification of the active airborne pathogen inactivation capabilities of
UVGI technologies with wavelengths in the UV-C range of 200 nm to 280 nm. It does this at productand application level.
The scope includes:• UVGI luminaires• UVGI air cleaners
See Section 3 for illustrative examples.
Not in scope are:
•
•
•
•

•
•
•

UV-A, UV-B and 405 nm technologies
UVGI lamps, UVGI light-sources and UVGI control-gearwater disinfection and surface disinfection technologies
UVGI devices which will be mounted in-duct in heating, ventilating and air-conditioning(HVAC) systems since these devices are already standardised in ISO 15714 (Method of
evaluating the UV dose to airborne microorganisms transiting in-duct ultraviolet germicidal
irradiation devices).
UVGI devices combining UVGI with mechanical filters (e.g. HEPA1 filters), chemicals and/or
additives.
ionisation air cleaning technologies
UVGI devices intended for use in medical treatment locations such as surgical suites,
laboratories and medical treatment rooms

The document does not describe UVGI safety requirements since they appear in existing
international standards IEC 62471:2006 (Photobiological safety of lamps and lamp systems), IEC PAS
63313:2021 (Position statement on germicidal UV-C irradiation - UV-C safety guidelines), ISO 15858(UV-C Devices - Safety information - Permissible human exposure), IEC 60335-2-65 (for closed UVGItechnologies) and IEC 63086-1:2020 (Household and similar electrical air cleaning appliances Methods for measuring the performance - Part 1: General requirements).

1

High Efficiency Particulate Air© Global Lighting Association 2022

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3. EXAMPLES OF UVGI OPERATING PRINCIPLESThis Section illustrates examples where no disinfection measures are taken (§3.1) and the operating
principles of UVGI air cleaners (§3.2) and UVGI luminaires (§3.3)
3.1

No disinfection measures

Figure 1: Illustrative example where no disinfection measures are taken
3.2

UVGI air cleaners

Figure 2: Illustrative example of UVGI air cleaner application© Global Lighting Association 2022

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3.3

UVGI luminaires

Figure 3: Illustrative example of a UVGI luminaire application

Figure 4: Illustrative example of UVGI upper-room luminaire application© Global Lighting Association 2022

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4. QUANTIFICATION OF MICROBIAL CLEANING CAPABILITIES OF UVGIPRODUCTS IN A TEST CHAMBER
In the 1980s, the Association of Home Appliance Manufacturers introduced Clean Air Delivery Rate
(CADR) as a standard metric for assessing the performance of air cleaners in reducing particles fromair (smoke, dust, pollen etc).
GLA encourages standards development organisations to endorse the decay rate2 method with themicrobial clean air delivery rate metric (CADRmicrobial) for assessing the performance of air cleaners forremoving and/or inactivating airborne pathogens in air. GLA also encourages standards development
organisations to standardise an equivalent decay rate method with an equivalent microbial clean air
delivery rate metric (eqCADRmicrobial) for assessing the performance of UVGI luminaires forinactivating airborne pathogens in air.
The CADRmicrobial of a UVGI air cleaner or the eqCADRmicrobial of a UVGI luminaire is determined by atest using nebulised and homogeneously distributed active (or surrogate) airborne pathogens inside
an enclosed test chamber with a volume of at least 20 m3 at controlled air temperature and relative
air humidity. The CADRmicrobial or eqCADRmicrobial is calculated by the reduction rate of the active
airborne pathogen in a defined period of time, considering the natural decay rate of the active
airborne pathogen and the volume of the test chamber.
Note 1: An air mixing in the enclosed test room is required to maintain a homogeneous distribution of the airborne
pathogens in the test room during the test.
Note 2: GLA recommends the usage of an active Coliphage PhiX-174 or MS2 surrogate pathogen since they are
fully benign bacteriophage viruses that are well studied [4,5].

For a UVGI air cleaner test results should be reported as CADRsurrogate-pathogen and for a UVGI luminaire
test results should be reported as eqCADsurrogate-pathogen
The final standardisation of CADRmicrobial and eqCADRmicrobial metrics should take place in the
responsible standards development organisations. Further guidance for this standardisation work isprovided in Annex A.

5. QUANTIFICATION OF MICROBIAL CLEANING CAPABILITIES OF UVGIPRODUCTS IN A REAL APPLICATION
Quantification of the microbial cleaning capabilities of UVGI products in a real application such as aroom can be determined by scaling-up the test chamber results of Section 4 to the volume andtarget pathogen of the room.
Section 5.1 below lists the various reduction mechanisms for active airborne pathogens in a room,
including their quantification by a decay rate. Recommended ventilation rates for different
applications are given in 5.2. Determination of the number of UVGI air cleaners required to meet
recommended UVGI equivalent ventilation rate in a room is given in 5.3. Determination of thenumber of UVGI luminaires required to meet recommended UVGI equivalent ventilation rate in aroom is given in 5.4.

2

Alternative test methods, such as steady state methods, are the subject of ongoing research© Global Lighting Association 2022

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5.1

Reduction mechanism for active airborne pathogens in a room and their genericquantification

Reduction of active airborne pathogens in a room can be achieved by:••••

Dilution of the active airborne pathogens by conventional (natural and/or mechanical) freshair ventilation, quantified by a decay rate called the ventilation rate, with the unit ACHfresh-air
Natural decay of the active airborne pathogens, quantified by a decay rate called the naturaldecay rate, with the unit ACHnatural-decay
Inactivation of the active airborne pathogens by engineering methods such as UVGI,quantified by a decay rate called the equivalent ventilation rate, with the unit eqACHUVGI3
A combination of the above, quantified by the total ventilation rate, with the unit ACHtot.

Note:

In general [6], the overall ventilation rate (ACH t ot ) is the sum of the ventilation rate (ACH fresh-air ), thenatural-decay rate (ACH natural-decay ) and the equivalent ventilation rate of the UVGI technology(eqACH UVGI ).

In general, the reduction is expressed in a decay rate with the unit Air Changes per Hour (ACH) in h-1.
The relationship is given in Equation 1.
𝐷𝑒𝑐𝑎𝑦 𝑅𝑎𝑡𝑒 =− 60 ln(𝑁𝑡 ⁄𝑁0 )𝑡(Equation 1)

Where:Nt,
N0t

is the number of active airborne pathogens after t minutes
is the initial number of active airborne pathogens at t = 0 minutes
is time in minutes

Note 1:

A decay rate of 1 ACH equals a 63.2% airborne pathogen reduction in one hour.

Note 2:

The above formulas assume that no further pathogen generation source is present in the room.

Note 3:The exponential decay of a microbial population in response to UV can be subject to a slight delay, also
known as ‘shoulder effect’. In many cases it can be neglected, especially for susceptible microbes or forhigh UV doses.

3

In the technical literature, equivalent air changes per hour is variously abbreviated as eACH, ACHeq or EAC .

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The relation and inverse relation between the reduction levels and reduction times on the one hand,
and the decay rates (ACH) on the other, are given in Table 1 and Table 2 respectively.
Decay rate (ACH) in h-1
Reduction level

Reduction
time [min]90%(Log 1)

99%(Log 2)

99.9%(Log 3)

10

13.8

27.6

41.4

20

6.9

13.8

20.7

30

4.6

9.2

13.8

40

3.5

6.9

10.4

50

2.8

5.5

8.3

60

2.3

4.6

6.9

Table 1: Relation between reduction levels and reduction times, and the decay rates
Note:

A log reduction is a measure of how thoroughly a decontamination process reduces the concentration of acontaminant. It is defined as the common logarithm of the ratio of the levels of contamination before and after
the process, so an increment of 1 corresponds to a reduction in concentration by a factor of 10. So for
example, a 0-log reduction is no reduction at all, while a 1 -log reduction corresponds to a reduction of 90
percent from the original concentration, and a 2-log reduction corresponds to a reduction of 99 percent fromthe original concentration (source: Wikipedia).

© Global Lighting Association 2022

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Decay
rate
(ACH)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
25
30
35
40
45
50

Reduction time [min]Reduction level
90%
99%
99.9%
(Log 1)(Log 2)(Log 3)
138
69
46
35
28
23
20
17
15
14
13
12
11
10
9
9
8
8
7
7
6
5
4
3
3
3

277
138
92
69
55
46
40
35
31
28
25
23
21
20
18
17
16
15
15
14
11
9
8
7
6
6

415
207
138
104
83
69
59
52
46
41
38
35
32
30
28
26
24
23
22
21
17
14
12
10
9
8

Table 2: Relation between decay rates and reduction levels and reduction times© Global Lighting Association 2022

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5.2

Recommended ventilation rates

The recommended total ventilation rate in a room (ACHtot, required) varies according to application anddepends on the required reduction level and reduction time for the airborne pathogens.
To reduce the contamination risk of viral infections like influenza, tuberculosis and SARS-CoV-2 inbuildings, GLA recommends the decay rates of Table 3 during a viral outbreak. These
recommendations are based on references [7,8].

Application
Buildings with vulnerable
people (such as hospitals,
elderly care)
Buildings inhabited by many
people for extended periods(such as offices, shops,
schools)
Other buildings

Recommended
total
ventilation rate
(ACHtot, required)

Recommended
fresh-airventilation rate
(ACHfresh-air)Natural-decay
rate(ACHnatural-decay)

Required UVGIequivalentventilation rate(eqACHUVGI)

≥ 15

3

0

≥ 12

≥ 10

3

0

≥7

≥6

2

0

≥4

Table 3: Recommended decay rates per application
Note 1: Above recommendations apply to the applicable areas/rooms in the building
Note 2: Above fresh-air ventilation rates are always recommended since fresh-air ventilation serves multiple
purposes other than dilution of airborne pathogens, including removal of harmful gasses such as CO2,
control of humidity levels (including condensation prevention) and reduction of undesirable odours.
Note 3: Key parameters driving the natural decay rate are ambient temperature, relative humidity and ambient UV index. In the technical literature, natural decay rates reported for SARS-CoV-2, at UV-index 0, typicallyrange from 0.2 to 2 ACH natural-decay . However by setting the natural decay rate to zero, a worst-case situation
is emulated.

5.3

UVGI air cleaner - relationship between required UVGI equivalent ventilation rate and
CADRsurrogate-pathogen

As a first order approach, the number of UVGI air cleaners needed to achieve the required UVGIequivalent ventilation rate of Section 5.2 in an arbitrary room with volume V depends on the
CADRsurrogate-pathogen of the UVGI air cleaner and can be determined with Equation 2.
# 𝑜𝑓 𝑈𝑉𝐺𝐼 𝑎𝑖𝑟 𝑐𝑙𝑒𝑎𝑛𝑒𝑟𝑠 =𝑘(𝜆)𝑠𝑢𝑟𝑟𝑜𝑔𝑎𝑡𝑒−𝑝𝑎𝑡ℎ𝑜𝑔𝑒𝑛
𝑒𝑞𝐴𝐶𝐻𝑈𝑉𝐺𝐼 ∙ 𝑉∙
𝐶𝐴𝐷𝑅𝑠𝑢𝑟𝑟𝑜𝑔𝑎𝑡𝑒−𝑝𝑎𝑡ℎ𝑜𝑔𝑒𝑛𝑘(𝜆)𝑡𝑎𝑟𝑔𝑒𝑡 𝑝𝑎𝑡ℎ𝑜𝑔𝑒𝑛(Equation 2)

where:# of UVGI air cleaners

is number of UVGI air cleaners needed to achieve the required
UVGI equivalent ventilation rate in the room

eqACHUVGI

is required UVGI equivalent ventilation rate (Section 6.2) in h-1

V

is volume of the room in m3

CADRsurrogate-pathogen

is CADR of the UVGI air cleaner according to the standards andtesting described in Section 5 in m3/h

© Global Lighting Association 2022

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is spectral susceptibility factor of airborne pathogens (m2/J) as
given in Table 4

k(λ)
Note:

Equation 2 does not consider application details , including objects within the space and non-uniform
placement of air cleaners.

In addition, the single pass efficacy (η) of the UVGI compartment of the UVGI air cleaner isrecommended to be η ≥ 0.95 at all airflow settings (Qm) to avoid cross contaminations by (horizontal)
airflows across the room induced by airflow of the UVGI air cleaner.
The single-pass efficacy, also known as removal rate, (η) of the UVGI compartment of a UVGI air
cleaner can be determined by Equation 3.

𝜂=

𝐶𝐴𝐷𝑅𝑠𝑢𝑟𝑟𝑜𝑔𝑎𝑡𝑒−𝑝𝑎𝑡ℎ𝑜𝑔𝑒𝑛(Equation 3)

𝑄𝑚

where:
Qm

5.4

is volumetric flow rate of air through the system in cubic metres per second (m3/h)

UVGI luminaire - relationship between required UVGI equivalent ventilation rate and
eqCADRsurrogate-pathogen

As a first order approach, the number of UVGI luminaires needed to achieve the required UVGIequivalent ventilation rate of Section 5.2 in an arbitrary room with volume V and a certain target
pathogen depends on the eqCADRsurrogate-pathogen of the UVGI luminaire and can be determined by
Equation 4.
𝑒𝑞𝐴𝐶𝐻𝑈𝑉𝐺𝐼 ∙ 𝑉# 𝑜𝑓 𝑈𝑉𝐺𝐼 𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒𝑠 = 𝑒𝑞𝐶𝐴𝐷𝑅

𝑠𝑢𝑟𝑟𝑜𝑔𝑎𝑡𝑒−𝑝𝑎𝑡ℎ𝑜𝑔𝑒𝑛∙𝑘(𝜆)𝑠𝑢𝑟𝑟𝑜𝑔𝑎𝑡𝑒−𝑝𝑎𝑡ℎ𝑜𝑔𝑒𝑛𝑘(𝜆)𝑡𝑎𝑟𝑔𝑒𝑡 𝑝𝑎𝑡ℎ𝑜𝑔𝑒𝑛(Equation 4)

where:

Note:# of UVGI luminaires

is number of UVGI luminaires needed to achieve the required UVGIequivalent ventilation rate in the room

eqACHUVGI

is required UVGI equivalent ventilation rate (Section 5.2) in h-1

V

is volume of the room in m3

eqCADRsurrogate-pathogen

is eqCADR of the UVGI luminaire as determined in Section 4 in m3/hk(λ)

is spectral susceptibility factor of airborne pathogens (m2/J) as
given in Table 4

Equation 4 does not consider application details including room/surface reflection, objects within the spaceand non-uniform placement of luminaires.

© Global Lighting Association 2022

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The classification and spectral susceptibility factors, k(λ), of some actual airborne pathogens at a
relative humidity (RH) below 68% are listed in Table 4.
UCGI
wavelength
λ in nm254

222

Classificationk(λ) in m2/J

SourceColiphage PhiX-174
MS-2
SARS-CoV-1
SARS-CoV-2
Influenza A (H1N1)
Tuberculosis (TBC)
Coliphage PhiX-174
MS-2
SARS-CoV-2

Non-enveloped DNA virus
Non-enveloped RNA virus
Enveloped RNA virus
Enveloped RNA virus
Enveloped RNA virus
Bacteria
Non-enveloped DNA virus
Non-enveloped DNA virus
Enveloped RNA virus

0.620
0.380
0.377
0.377
0.270
0.472

ISO 15714
ISO 15714
Walker
Beggs
KowalskiISO 15714

Brenner

Influenza A (H1N1)
Tuberculosis (TBC)

Enveloped RNA virus
Bacteria

0.4104 0.5905
0.180

Airborne pathogen

BrennerTable 4: Classification and spectral susceptibility factors, k(λ), of some actual airborne pathogens
Note 1:More spectral susceptibility factors are given by Kowalski [4] and standard ISO 15714 (Method of
evaluating the UV dose to airborne microorganisms transiting in -duct ultraviolet germicidal irradiation
devices)

Note 2:

Spectral susceptibility factors at a relative humidity above 68% are given by Kowalski [4]Note 3:

Missing spectral susceptibility factors in Table 4, k(λ), are a subject for research

45Alpha coronavirus (HCoV-229E)
Beta coronavirus (HCoV-OC43)© Global Lighting Association 2022

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6. TERMS AND DEFINITIONS
Ultraviolet germicidal irradiation (UVGI)
Method for disinfection of air, water and object surfaces that uses radiation with a wavelength in
the range 200 nm to 280 nm to kill or inactivate microorganisms and viruses
Note: UV irradiation with a wavelength of 200 nm to 280 nm can cause damage to the DNA or RNAof the microorganisms or viruses.
[Source: ISO 15714:2019, 3.1.5 modified by lowering 240 nm to 200 nm and extended to viruses]UVGI air cleaner
Electrically powered household, or similar, appliance that employs UVGI technologies to inactivate
one or more types of airborne pathogens using a forced air flow through a closed UVGI
compartment.
[Source: IEC 63086-1 modified]UVGI luminaire
Apparatus which distributes, filters or transforms UVGI from at least one UVGI source and which
includes all parts necessary for fixing and protecting the UVGI source and, where necessary, circuit
auxiliaries together with the means for connecting them to the power supply.
[Source: IEC 60050-845; 845-30-001: 2020 modified]UVGI upper-air luminaire
UVGI luminaire mounted underneath room ceilings with UVGI directed to the upper part of theroom with adjustable louvers to keep UVGI above eye and head level.
[Source: ISO 15858: 2016 modified]© Global Lighting Association 2022

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7. REFERENCES[1] Wells WF, Fair MG. “Viability of B. coli exposed to ultra-violet radiation in air”, Science, Volume
82, Issue 2125, pp. 280-281, 1935
[2] McLean, R.L., “The effect of ultraviolet radiation upon the transmission of epidemic influenza inlong-term hospital patients”, American Review of Respiratory Diseases 83(2): 36–8, 1961
[3] Anca Maria Moldoveanu, “Biological Contamination of Air in Indoor Spaces”, Current Air Quality
Issues, IntechOpen, DOI: 10.5772/59727, 2015[4] W. Kowalski, “Ultraviolet Germicidal Irradiation Handbook, UVGI for Air and Surface
Disinfection”, 2009[5] Yoram Gerchman, “UV-LED disinfection of Coronavirus: Wavelength effect”, Journal of
Photochemistry and Photobiology, Volume 212, 2020
[6] Shelly Miller, “EFFICACY OF ULTRAVIOLET IRRADIATION IN CONTROLLING THE SPREAD OF
TUBERCULOSIS”, CDC/NIOSH report 2002
[7] IES-CR-2-20-V1-6d[8] https://www.cdc.gov/infectioncontrol/guidelines/environmental/appendix/air.html© Global Lighting Association 2022

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ANNEX
Determination of CADR or eqCADR of UVGI productAs stated in Section 4, the Global Lighting Association encourages standards development
organisations (SDOs) to endorse the decay rate method with CADRmicrobial or eqCADRmicrobial metrics
for airborne pathogen removal and/or inactivation performance assessment of UVGI air cleaners
and UVGI luminaires respectively.
This informative Annex provides the basic steps for CADRmicrobial or eqCADRmicrobial determination. The
measurement details must be worked out by the responsibleSDOs. GLA anticipates that SDOs may
improve the steps outlined in this informative annex and welcomes enhancements in test efficiency,
accuracy, repeatability and reproducibility.
UVGI products to be tested are referred to in this Annex as device under test (DUT).
Step 1: Pathogen selection and test setup
1.1 Select target pathogen, or a surrogate pathogen with comparable UVGI susceptibility to thetarget pathogen.
1.2 If applicable, apply burn-in time of the DUT as prescribed by the manufacturer.
1.3 Select an enclosed test chamber with:- defined volume of test room
- defined UV-C reflectance (%) of walls, floor and ceiling- controlled air temperature- controlled relative air humidity.
1.4 Install the DUT in the selected enclosed test chamber following manufacturer’s installation
instructions and approximate the intended application.
Step 2: Determine natural decay rate without operating the DUT
2.1 Close the test-chamber and control and record air temperature and relative humidity inside thetest-chamber.
2.2 Nebulise the test-chamber with a quantified initial concentration colony forming units (CFU), N0(CFU/m3), of the selected pathogen using a calibrated nebuliser.
2.3 Determine the measurement time (t) to assure a good natural decay value.
Note: The standard should include methodology for determining measurement times that assure good natural
decay value - for example, with specific standard times and/or a standardised approach for determining
test-specific times.

2.4 Activate the test-chamber’s stirring fan to assure a homogeneous pathogen concentration in thetest chamber
Note: To achieve an initial homogenous mixing of the pathogen in the test chamber, a period of mixing before
step 2.5 is required. Any additional mixing throughout the test should be carefully specified by the SDO
to ensure consistent and unbiased results.

2.5 Take a sample at measurement time t.
Note: The standard should standardise the sampling method (quantity of samples, duration etc.) in a mannerthat best represents conditions throughout the chamber and be repeatable and reproduceable.

2.6 Determine the concentration CFU of the pathogen, Nt (CFU/m3), at time t.

© Global Lighting Association 2022

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2.7 Calculate the natural decay rate with Equation 4.
ACHnatural decay = (60/t)(ln N0/Nt)(4)where:
t is measurement time at time point t in minutes
Nt is CFU concentration of the pathogen at time point t, in CFU/m3
N0 is initial CFU concentration of the pathogen, in CFU/m3
2.8 Deactivate the chamber’s stirring fan.
2.9 Ventilate/disinfect the test-chamber.
Step 3: Determine decay rate of the pathogen when DUT is operating
3.1 Activate the DUT and, if applicable, apply the stabilisation time of the DUT as prescribed by the
manufacturer, and nebulise the test-chamber with a quantified initial concentration CFU, N0(cfu/m3), of the selected pathogen using a calibrated nebuliser.
3.2 Determine the measurement time (t) to assure a good natural decay value.
Note:

The standard should include methodology for d etermining measurement times that assure goodnatural decay value - for example, with specific standard times and/or a standardised approach for
determining test-specific times.

3.3 Activate the test-chamber’s stirring fan to assure a homogeneous pathogen concentration in thetest chamber
Note:

To achieve an initial homogenous mixing of the pathogen in the test chamber, a period of mixing
before step 3.5 is required. Any additional mixing throughout the test should be carefully specified
by the SDO to ensure consistent and unbiased results.

3.4 Take a sample at measurement time t.
Note:

The standard should standardise the sampling method (quantity of samples, duration, etc.) in amanner that best represents conditions throughout the chamber and be repeatable andreproduceable.

3.5 Determine concentration CFU of the pathogen, Nt (CFU/m3), at time t.
3.6 Calculate total decay rate, (eq)ACHtotal, with Equation 5.
(eq)ACHtotal = (60/t)(ln N0/Nt)(5)where:
t is measurement time at time point t in minutes
Nt is CFU concentration of the pathogen at time point t, in CFU/m3
N0 is initial CFU concentration of the pathogen, in CFU/m3
3.7 Deactivate DUT and the chamber’s stirring fan.
3.8 Ventilate/disinfect test-chamber and open it.
Step 4: Calculate the CADRsurrogate or eqCADRsurrogate value
4.1 Calculate UVGI decay rate, (eq)ACHUVGI, according to:(eq)ACHUVGI = ACHtotal – ACHnatural decay
4.2 Calculate (equivalent) clean air delivery rate according to:(eq)CADRsurrogate = (eq)ACHUVGI x Vtest© Global Lighting Association 2022

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Step 5: Reporting
5.1 Report (eq)CADRsurrogate in (m3/h) at each tested configuration
5.2 Report test condition details such as:- test laboratory details such as: name, location, date, operator.
- test chamber details such as:- volume of the test-chamber, Vtest in m3, and its length, width, and height in m
- UV-C reflectance (%) of the test-chamber walls, floor, and ceiling- selected pathogen or surrogate pathogen and its susceptibility factor, k(λ), in m2/J
- initial CFU concentration of the pathogen, in CFU/m3- temperature, humidity- device mounting location and mounting details including photographs- pre-mixing fan airflow and in-test mixing airflow- time of overall test and sampling times- nebuliser details (particle sizes, locations, timing etc.)- sampling locations, time, sampling method/equipment, details on method of analysis- chamber ventilation details that could impact interpretation of the test including air
filters- initial and during test mixing fan details (airflow) and locations- chamber air clean-up method and disinfection method
5.3 Report DUT details such as:- manufacturer- DUT type and model number- voltage in V, and power in W, and air flow settings in m3/h
- peak wavelength(s) (λ) in nm- inclusion of pre-filter (if any)

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