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Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series Colour fastness to Light 1 The complaints of poor colour fastness when sports dress loses color and form, the seat fabric inside of a car or the carpet fades too fast are very common. All dyes will fade when exposed to sunlight and it is possible for a dyed article to fade noticeably during drying on a washing line in bright sunlight or, more importantly, under display lighting conditions in a retail outlet. Any reputable retailer would, however, regard such a level of performance as quite unacceptable. Testing for light fastness provides an objective framework for what is acceptable. Fastness to light is basically a feature of the actual colourant molecule itself; it is, in fact, a measure of the ability of the molecule to absorb radiation without being destroyed, the absorbed radiation being dissipated in other ways. In a dye with poor light fastness the molecule will be broken down by the absorbed radiation. No colourant is completely fast to light, but it should be emphasized that this is not of real importance. All that matter is the colourant should not fade appreciably during the life of the article. Lightfastness is the degree to which a colourant resists fading due to light exposure. Different dyes have different degrees of resistance to fading by light. All colourants have some susceptibility to light damage, simply because their colors are indications that they absorb the wavelengths that they do not reflect. Light is energy, and the energy that is absorbed by the colourant compounds degrade them or nearby molecules. The resistance to degradation (or fading) of fabric dyes and prints due to light is therefore an important requirement of a garment because without such resistance, the garment may change colour and such colour may not be acceptable to the customer. Retailers are also becoming more aware of issues concerning colour fastness to light. Higher colour fastness is now being demanded for apparel that will be worn predominantly outdoors. Another technical issue is the problem of accelerated colour fading on exposure to light in alkaline or acidic perspiration through the intense physical activity of the wearer. Nowadays the criteria of light fastness is hence becoming a major concern amongst buyers and consequently with dyers. Standard Methods of light fastness: Standard Methods of light fastness: Standard Methods of light fastness: Standard Methods of light fastness: Generally two methods of testing are widely accepted by most of the customers. They are: 1. American Test Method (AATCC 16, Option 3) 2. ISO Test Method (ISO 105/BO2) Both the methods recommend the use of artificial light source, namely Xenon Arc lamp exposure as it is representative of natural daylight. The graph below shows the comparison of sunlight with the artificial light produced by the xenon arc lamp. COLOUR FASTNESS TO LIGHT

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Page 1: Colour fastness to Light - Texanlabtexanlab.com/documents/downloads/9.pdf · (change in colour) correspondingtogreyscale grade4andlatertogrey ... Assessment The light fastness rating

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������1�

�������������The� complaints�of� poor� colour� fastness�when� sports�dress� loses� color� and� form,� the� seat� fabric�inside�of�a�car�or�the�carpet�fades�too�fast�are�very�common.�All�dyes�will� fade�when�exposed�to�sunlight�and�it�is�possible�for�a�dyed�article�to�fade�noticeably�during�drying�on�a�washing�line�in�bright� sunlight� or,�more� importantly,� under� display� lighting� conditions� in� a� retail� outlet.� Any�reputable� retailer� would,� however,� regard� such� a� level� of� performance� as� quite� unacceptable.�Testing�for�light�fastness�provides�an�objective�framework�for�what�is�acceptable.��Fastness�to�light�is�basically�a�feature�of�the�actual�colourant�molecule�itself;�it�is,�in�fact,�a�measure�of�the�ability�of�the�molecule�to�absorb�radiation�without�being�destroyed,�the�absorbed�radiation�being�dissipated�in�other�ways.�In�a�dye�with�poor�light�fastness�the�molecule�will�be�broken�down�by�the�absorbed�radiation.�No�colourant�is�completely�fast�to� light,�but�it�should�be�emphasized�that� this� is�not�of� real� importance.�All� that�matter� is� the� colourant� should�not� fade� appreciably�during�the�life�of�the�article.��Lightfastness�is�the�degree�to�which�a�colourant�resists�fading�due�to�light�exposure.�Different�dyes�have�different�degrees�of�resistance�to�fading�by�light.�All�colourants�have�some�susceptibility�to�light� damage,� simply� because� their� colors� are� indications� that� they� absorb� the�wavelengths� that�they�do�not�reflect.�Light�is�energy,�and�the�energy�that�is�absorbed�by�the�colourant�compounds�degrade�them�or�nearby�molecules.��The� resistance� to� degradation� (or� fading)� of� fabric� dyes� and� prints� due� to� light� is� therefore� an�important� requirement�of�a� garment�because�without� such� resistance,� the� garment�may� change�colour�and�such�colour�may�not�be�acceptable�to�the�customer.��Retailers� are� also� becoming� more� aware� of� issues� concerning� colour� fastness� to� light.� Higher�colour� fastness� is� now�being�demanded� for� apparel� that�will� be�worn�predominantly� outdoors.�Another�technical�issue�is�the�problem�of�accelerated�colour�fading�on�exposure�to�light�in�alkaline�or�acidic�perspiration�through�the�intense�physical�activity�of�the�wearer.��Nowadays� the�criteria�of� light� fastness� is�hence�becoming�a�major�concern�amongst�buyers�and�consequently�with�dyers.��Standard�Methods�of�light�fastness:Standard�Methods�of�light�fastness:Standard�Methods�of�light�fastness:Standard�Methods�of�light�fastness:�����Generally�two�methods�of�testing�are�widely�accepted�by�most�of�the�customers.�They�are:��

1. American�Test�Method�(AATCC�16,�Option�3)��2. ISO�Test�Method�(ISO�105/BO2)��

�Both�the�methods�recommend�the�use�of�artificial�light�source,�namely�Xenon�Arc�lamp�exposure�as�it�is�representative�of�natural�daylight.��The�graph�below�shows�the�comparison�of�sunlight�with�the�artificial�light�produced�by�the�xenon�arc�lamp.��

COLOUR�FASTNESS�TO�LIGHT�

Page 2: Colour fastness to Light - Texanlabtexanlab.com/documents/downloads/9.pdf · (change in colour) correspondingtogreyscale grade4andlatertogrey ... Assessment The light fastness rating

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������2�

��

���Test�procedure�in�briefTest�procedure�in�briefTest�procedure�in�briefTest�procedure�in�brief��������

Summary� :� �Summary� :� �Summary� :� �Summary� :� � � A� specimen� of� textile� is� exposed� to� artificial� light� source� under� specified�conditions� together� with� dyed� blue� standards� having� known� fading� characteristics.� The�fastness�is�evaluated�by�comparison�of�the�colour�change�of�the�specimen�with�that�of�the�standards�under�standard�viewing�conditions.��

ParameteParameteParameteParametersrsrsrs���� ISO�105�B02ISO�105�B02ISO�105�B02ISO�105�B02���� AATCC�TM�16�(option�3)AATCC�TM�16�(option�3)AATCC�TM�16�(option�3)AATCC�TM�16�(option�3)����Apparatus�and�Materials:Apparatus�and�Materials:Apparatus�and�Materials:Apparatus�and�Materials:����

Apparatus�

Xenon� Arc� lamp� light� fastness� tester� equipped� with� a�xenon� lamp,� suitable� filter� systems� and� various� control�systems� (Water� or�Air� cooled� type);� Specimen� holders;�Masks;� Black� Standard� Temperature� (for� ISO)� Black�Panel� Thermometer� (for� AATCC);� Colour� Matching�Cabinet�

Humidity�Test�Control�fabric�Red�Azoic�dyed�cotton�

cloth�-�

Blue�Wool�Light�fastness��reference�standards�

1�to�8� L�2�to�L�9�

Humidity�Test�Control�fabric�Red�Azoic�dyed�cotton�

cloth�-�

Temperature�Control�fabric� -�Xenon�reference�fabric�

(polyester�dyed)�

Xenon with Window Glass Filters

0.0

0.5

1.0

1.5

2.0

2.5

3.0

250 300 350 400 450 500 550 600 650 700 750 800

Wavelength (nm)

Irra

dia

nce (W

/m²/nm

)

Xenon with Window

Glass Filters

Sunlight Through

Window Glass

Sunlight

Page 3: Colour fastness to Light - Texanlabtexanlab.com/documents/downloads/9.pdf · (change in colour) correspondingtogreyscale grade4andlatertogrey ... Assessment The light fastness rating

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������3�

Exposure�conditions:Exposure�conditions:Exposure�conditions:Exposure�conditions:����Normal�(Moderate�effective�humidity)Normal�(Moderate�effective�humidity)Normal�(Moderate�effective�humidity)Normal�(Moderate�effective�humidity)�L.F.�of�humidity�test�control� 5� -�Max.�Black�standard�temp.� 45º�C� -�Extreme�conditions�(Low�effective�humidExtreme�conditions�(Low�effective�humidExtreme�conditions�(Low�effective�humidExtreme�conditions�(Low�effective�humidity)ity)ity)ity)�L.F.�of�humidity�of�test�control� 6-7� -�Relative�humidity�of�air� -� 30�±�5%�Max.�black�panel�/�standard�temp.�

60º�C� 63�±�1º�C�

Chamber�air�temperature� -� 43�±�2º�C�Irradiance�at�420�nm�or�300-400�nm�

1.1�W/m2/nm�for�water�

cooled�machines�1.10�±�0.03�W/m

2/nm�or�48�

±�1�W/m2�

Extreme�conditions�(High�effective�humidity)Extreme�conditions�(High�effective�humidity)Extreme�conditions�(High�effective�humidity)Extreme�conditions�(High�effective�humidity)����L.F.�of��humidity�test�control� 3� -�Max.�black�panel�temp.� 40º�C� -�

Length�of�exposureLength�of�exposureLength�of�exposureLength�of�exposure�

Expose� until� a� contrast�(change� in� colour)�corresponding� to� grey� scale�grade� 4� and� later� to� grey�scale�3� is�visible�on� the� test�sample,� but� at� most� until�the� blue� wool� reference� 7�shows� a� contrast�corresponding� to� grey� scale�grade�4��Expose�to�a�certain�level�of�irradiance�is�attained;�H�=�E�x�3.6�x�t�where�H�is�the�radiant�exposure�in�kilojoules�per�square�metre;�E�is�the�irradiance�in�watts�per�square�metre�(or�joules�per�square�metre�and�second;�t�is�the�time�in�hours�and�3.6�is�a�conversion�factor�

Expose�until�a�certain�stage�is�reached�and�then�assess�with�the�grey�scale.�This�will�vary�depending�on�the�material;�The�least�durable�exposed�for�least�amount�of�time�(20�accelerated�fading�units�(AFU)�corresponding�to�reference�sample�L4);�40�AFU�of�exposure�for�upholstery�(equivalent�to�L5,�Draperies�60�AFU�and�so�on.��L6�is�equivalent��to�80�hours,�It�is�rare�for�clothing�to�require�a�light�fastness�higher�than�L5����

AssessmentAssessmentAssessmentAssessment���� The� light� fastness� rating�corresponds� to� the�number�of� the� blue� wool� reference�on� the� light� fastness� scale�which� shows� a� similar�contrast.��Rating�between�BWS�1�and�BWS�8�

Using� Colour� Change� Grey�Scale�1-5�

Page 4: Colour fastness to Light - Texanlabtexanlab.com/documents/downloads/9.pdf · (change in colour) correspondingtogreyscale grade4andlatertogrey ... Assessment The light fastness rating

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������4�

��������Comparison�between�commonly�followed�ISO�and�AATCC�testing�methodsComparison�between�commonly�followed�ISO�and�AATCC�testing�methodsComparison�between�commonly�followed�ISO�and�AATCC�testing�methodsComparison�between�commonly�followed�ISO�and�AATCC�testing�methods�����There�is�often�confusion�between�the�two�tests�in�the�minds�of�people�not�familiar�with�the�test�procedures.��The�methods�have�two�distinct�differences�in�terms�of�assessment�and�“duration”�of�testing.��Often,�the�AATCC�method�is�incorrectly�asked�for�a�number�of�hours�whereas�the�correct�measure�is�Accelerated�Fading�Units�or�AFU.����Test�conditions�are�also�different,�as�detailed�in�the�earlier�section.��Typically,�the�most�common�ISO�test�is�conducted�at�low�effective�humidity�(extreme�conditions).��As�a�summary,�the�following�table�shows�the�major�differences.��

ParameterParameterParameterParameter���� ISO�105�B02ISO�105�B02ISO�105�B02ISO�105�B02���� AATCC�16AATCC�16AATCC�16AATCC�16����Assessment� Blue�Wool�Scale�1�to�8� Standard�Grey�Scale�1�to�5�Duration�of�test� Not�relevant.��Test�completed�

when�sample�shows�specific�fading.�

Defined�by�Buyers,�typically�20�AFU�for�apparel,�higher�for�home�textiles��

Temperature� Black�Standard�Thermometer� Black�Panel�Thermometer���Factors�affecting�Light�FastneFactors�affecting�Light�FastneFactors�affecting�Light�FastneFactors�affecting�Light�Fastness�Ratingsss�Ratingsss�Ratingsss�Ratings�����There�are�quite�a�few�issues�that�affect�colourfastness�to�light.��Some�of�these�are�discussed�below�–��

1.1.1.1. Dyestuff�usedDyestuff�usedDyestuff�usedDyestuff�used�����

The� colourfastness� to� light� is� a�property�of� the� colourant�molecules� themselves.� �Therefore,�selection�of�colourants�clearly�influences�the�light�fastness�property.��Combination�shades�also�are�affected�by�the�light�fastness�of�individual�dyes.�

�2.2.2.2. Dye�shade�/�depthDye�shade�/�depthDye�shade�/�depthDye�shade�/�depth����

�Unlike�other�colourfastness�tests,�a�higher�shade�depth�gives�much�better�light�fastness�ratings�than�a�pale�shade�of�the�same�combination.�

�3.3.3.3. Fabric�surfaceFabric�surfaceFabric�surfaceFabric�surface����

�It�has�been� found� that� the� surface� area�of� the� fabric� can�greatly� affect� the� colourfastness� to�light.� �As� an� example,� see� the� example�below.� �One� is� a� single� jersey� fabric� and� the�other�a�pique.��Both�were�dyed�in�the�same�bath�for�the�purposes�of�testing�and�a�marked�difference�was� seen� in� the� light� fastness.� �The�pique� construction� showed�a�much�worse� light� fastness�than�the�single�jersey.�

�4.4.4.4. Finishing�chemicalsFinishing�chemicalsFinishing�chemicalsFinishing�chemicals����

�Some� finishing� chemicals� can� also� affect� the� light� fastness� ratings.� �While� there� is� not� too�much�information�on�which�chemicals�do,�it�is�a�point�to�be�kept�in�mind�by�processors.�

Page 5: Colour fastness to Light - Texanlabtexanlab.com/documents/downloads/9.pdf · (change in colour) correspondingtogreyscale grade4andlatertogrey ... Assessment The light fastness rating

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������5�

�Summary�of�Important�Issues�for�ProcessorsSummary�of�Important�Issues�for�ProcessorsSummary�of�Important�Issues�for�ProcessorsSummary�of�Important�Issues�for�Processors�����

• Selection�of�Dyestuff�must�be�made�based�on�requirements�and�end�use�

• Remember�lighter�shades�give�poorer�light�fastness�properties�

• Finishing�chemicals�can�affect�lightfastness..��

Example�of�fabric�with�poor�Example�of�fabric�with�poor�Example�of�fabric�with�poor�Example�of�fabric�with�poor�colourfastness�to�light.colourfastness�to�light.colourfastness�to�light.colourfastness�to�light.����

� ����� ����

Water�cooled�light�fastness�Water�cooled�light�fastness�Water�cooled�light�fastness�Water�cooled�light�fastness�machinemachinemachinemachine����

� ����

Page 6: Colour fastness to Light - Texanlabtexanlab.com/documents/downloads/9.pdf · (change in colour) correspondingtogreyscale grade4andlatertogrey ... Assessment The light fastness rating

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������6�

Arrangement�of�water�cooled�Arrangement�of�water�cooled�Arrangement�of�water�cooled�Arrangement�of�water�cooled�xenon�arc�lampxenon�arc�lampxenon�arc�lampxenon�arc�lamp����

� ����

Variation�in�light�fastness�due�to�Variation�in�light�fastness�due�to�Variation�in�light�fastness�due�to�Variation�in�light�fastness�due�to�differences�in�knit�structuredifferences�in�knit�structuredifferences�in�knit�structuredifferences�in�knit�structure����

� ����

Page 7: Colour fastness to Light - Texanlabtexanlab.com/documents/downloads/9.pdf · (change in colour) correspondingtogreyscale grade4andlatertogrey ... Assessment The light fastness rating

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������7�

Blue�wool�standards�Blue�wool�standards�Blue�wool�standards�Blue�wool�standards�––––�ISO�105�B02��ISO�105�B02��ISO�105�B02��ISO�105�B02�test.test.test.test.����BWS�1�to�BWS�5,�showing�BWS�1�to�BWS�5,�showing�BWS�1�to�BWS�5,�showing�BWS�1�to�BWS�5,�showing�geometric�progression�of�fadinggeometric�progression�of�fadinggeometric�progression�of�fadinggeometric�progression�of�fading����

����