Why Fabric Fails Lightfastness Testing After Approval

Why does fabric fail lightfastness testing even after a development sample has passed?

Sometimes the material cannot retain its shade under the specified light exposure. In other cases, the specimen submitted to the laboratory does not represent the condition of the bulk fabric.

Both issues appeared in an actual dark army green, 100% nylon project. The requirement was Grade 4 or above under AATCC TM16.3. The fabric was below Grade 4 before the selected finishing treatment. After the bulk fabric was re-finished and tested again using the same method, it achieved Grade 4 or above.

The case also exposed a more serious sourcing risk: a test-only length had been exposed to sunlight before submission. That specimen passed, but the original bulk fabric failed.

What a Lightfastness Failure Actually Means

Lightfastness describes how well a textile colour resists change under defined light exposure conditions.

AATCC TM16.3 uses xenon-arc light exposure to evaluate the colourfastness of textile materials. It can be applied to fibres, colourants, finishes and treatments used on textiles.

A fabric fails when the colour change after the specified exposure is greater than the buyer’s acceptance limit.

In this project, the agreed requirement was Grade 4 or above. This was a project specification, not a universal requirement for every nylon fabric or outdoor garment.

The test method number alone is also insufficient. The parties should agree on the applicable test option, exposure conditions, evaluation requirement and minimum acceptable grade.

A xenon-arc result does not translate directly into an exact number of days or months of outdoor use. Laboratory exposure and actual conditions during use are related, but they are not identical.

Why Fabric Fades in Sunlight or Xenon-Arc Testing

There is no single answer to why fabric fades in sunlight or fails a xenon-arc lightfastness test.

The result can be affected by:

• Fibre composition

• Dye and colourant selection

• Colour recipe

• Shade depth

• Dyeing process control

• Heat history

• Subsequent finishing

• The specified exposure and evaluation conditions

A colour name such as army green is not a technical performance specification. Two fabrics described as dark army green may use different dye combinations, processing routes and finishing treatments.

In CC Textile’s project experience, dark army green has required particular attention because an unacceptable shade change can be visually obvious. A composite shade may also change in hue if its colour components do not respond to light exposure in the same way.

This does not mean that every army green nylon fabric will fail. It means buyers should approve the actual colour and final finishing route through testing instead of relying on the shade name or an earlier lab dip.

UPF Is Not the Same as Colourfastness to Light

UPF and colourfastness to light are different fabric properties.

AATCC TM183 is used to determine the ultraviolet radiation blocked or transmitted by fabric intended for UV protection. AATCC TM16.3 evaluates how the textile colour changes under xenon-arc light exposure.

A fabric can therefore provide a specified level of UV protection without automatically meeting a lightfastness requirement. It may also have acceptable lightfastness without carrying a defined UPF specification.

In the dark army green nylon project, the selected UPF finishing route was supported by before-and-after AATCC TM16.3 reports:

• Before finishing: below Grade 4

• After finishing: Grade 4 or above

This result applies to that fabric, colour recipe and production route. It should not be interpreted as evidence that every UPF finish will improve the lightfastness of every fabric.

For a new colour or construction, buyers should define and test UPF and lightfastness as separate requirements.

When the Approved Test Sample Does Not Represent Bulk

One of the largest risks in fabric testing is not always the laboratory method. It is the condition of the sample sent to the laboratory.

In the project discussed here, a two-metre length selected for testing had been exposed to sunlight before submission. The dark army green changed towards a noticeably paler, whitish green.

The submitted sample passed the test, but the bulk fabric, which had not received the same pre-exposure, failed.

The problem was not simply that the bulk and test specimen produced different numbers. The submitted specimen no longer represented the actual condition of the bulk production.

Undisclosed pre-conditioning creates several buyer risks:

• The report cannot be reliably connected to the production lot.

• The approved sample may differ visibly from the required bulk shade.

• Bulk inspection or garment testing can reveal the failure later.

• Re-finishing and repeat testing can delay delivery.

• The buyer may have a passing report without having compliant bulk fabric.

Any conditioning or treatment required by the agreed test method should be documented. A test-only treatment that is not applied to bulk production should not be used as evidence of bulk performance.

This principle applies beyond lightfastness. As explained in our article on outdoor fabric testing and garment failure, a report confirms the result of the submitted specimen under defined conditions. It does not automatically verify every roll or every finished garment.

How the Bulk Fabric Was Corrected

The affected material was a dark army green, 100% nylon woven fabric.

The agreed lightfastness requirement was AATCC TM16.3 Grade 4 or above. Testing before the corrective finishing route produced a result below Grade 4.

The bulk fabric was then processed again with the selected UPF finish. After re-finishing, it was retested using the same AATCC TM16.3 method and achieved Grade 4 or above.

The corrective process therefore included:

• Re-finishing the actual bulk fabric

• Testing the final finished material

• Using the same lightfastness test method

• Confirming a result of Grade 4 or above

Testing the final finished fabric was essential. A result from an earlier development sample would not have confirmed whether the reprocessed bulk met the requirement.

The outcome was project-specific. A different nylon construction, colour recipe or finishing route would require separate evaluation.

What Buyers Should Specify Before Testing

A request such as “good lightfastness” is open to interpretation. A workable specification should define measurable acceptance conditions.

Before placing a bulk order, buyers should confirm:

• Fabric composition and construction

• Approved colour reference or lab dip

• Lightfastness test method and applicable version

• Test option and exposure conditions where required

• Minimum acceptable colour-change grade

• Required finishing route

• The production stage at which testing will occur

• Whether the specimen must be taken from final finished bulk

• How the production lot, roll and cutting location will be recorded

• Whether any pre-conditioning is permitted

• Retesting and corrective-action requirements

• Whether written approval is required before shipment

If UPF performance is also required, it should have its own method, target and testing conditions. It should not be treated as another name for colourfastness.

Our quality and compliance process connects the approved specification, final finishing route and required testing with bulk production.

Why a Low Fabric Price Can Become Expensive

A low quotation does not automatically indicate poor fabric. However, two quotations cannot be compared fairly if they include different finishing, testing and production controls.

A performance finish adds material, processing and quality-control costs. If the original quotation does not include the required treatment, the supplier may later need to renegotiate the price, absorb the additional cost or omit part of the intended process.

For the buyer, an omitted requirement can lead to:

• Bulk lightfastness failure

• Re-finishing costs

• Additional laboratory testing

• Colour changes after corrective processing

• Garment production delays

• Missed shipment dates

• Disputes over responsibility

The apparent saving on the fabric price can become small compared with the cost of reprocessing completed bulk fabric or delaying garment production.

Buyers should therefore ask whether the quotation includes the required finishing route, bulk testing and corrective-action responsibility. Price should be compared against an identical specification and approval scope.

A Practical Lightfastness RFQ Requirement

A buyer could write the project requirement as follows:

100% nylon woven fabric in dark army green. Lightfastness to be tested according to AATCC TM16.3 using the mutually agreed option and exposure conditions. Required colour-change result: Grade 4 or above. The submitted specimen must be selected from final finished bulk production, and any pre-conditioning must be declared. UPF performance, if required, must be specified and tested separately.

The final wording should still be reviewed against the garment application, customer manual and appointed laboratory requirements.

The Buyer’s Main Control Point

Fabric lightfastness testing is not only about obtaining a passing report. The report, test specimen and bulk fabric must all refer to the same construction, colour and finishing condition.

The dark army green nylon project showed three separate lessons:

• UPF and lightfastness are different properties.

• A project-specific finish may affect both, but the result must be verified.

• A passing test-only specimen does not approve bulk fabric when the specimen is not representative.

If buyers have a fabric sample, colour standard, AATCC requirement or previous failure report, they can discuss the specification and fabric development route with CC Textile before bulk production.

For project evaluation, contact CC Textile. We also share woven fabric development and testing notes through CC Textile on LinkedIn.