A simple guide to Light fastness testing: helping brands show their true colours

In our latest blog, our Applications Specialists share their expertise and explore the issues surrounding this essential technology, and the University of Leeds explain how the TruFade Light Fastness Tester has aided their research and expertise.

Of all the types of colour fastness testing, gauging a material’s reaction to light is probably one of the most important. How fabrics perform during washing, dry-cleaning, rubbing, perspiration; or following exposure to different kinds of water, is of course vital information for manufacturers. But the effects of light can be far more subtle and unpredictable, so it’s here that accurate, reliable testing is crucial.

Anticipating light fastness correctly can be a question of make or break for some businesses. A new product whose colour starts to fade too quickly could damage a company’s reputation for years. Imagine a swimsuit that fades in the sunshine? Without thorough, efficient testing, these scenarios would be all too common.

What is Light Fastness Testing?

Light fastness testing is a specific type of Colour Fastness Testing, where its purpose is to subject your test samples to intense artificial light to assess the impact on the material. At a commercial level, light fastness testing gives manufacturers confidence in their products, explains Product Manager Alan Thomson: “It helps them extend ranges, enter new markets and develop innovative materials ahead of their competitors. It also enables them to meet national, international and retailers’ standards. And it means they can experiment with a range of new products – and know they’ve got them right before launching them.”

The best way to test

“For many industries, light fastness testing is a fundamental part of research and development and quality control. Exposing your samples to natural sunlight in the location where they’re going to be used is impractical, as most materials this can take months or even years – and how many R&D departments can afford to wait that long?”, says Alan.

Instead, most manufacturers now use laboratory testers, which simulate natural light and speed up the testing process. The technology which does this most successfully is xenon long arc radiation. “This is the only way to reproduce faithfully the sunlight spectrum, and it involves using different optical filters to replicate specific light conditions,” adds Peter Goodwin, Head of Technical. “James Heal’s TruFade light fastness tester simulates natural light using continuous wave technology – meaning the lamp stays on during the test, to maximise the samples’ exposure to light.”

Don’t just look at the light

“It’s not as simple as putting a material under a certain type of light and observing how it performs,” explains Peter. “Temperature and humidity must also be brought into the equation, because the stress they cause to many materials can have profound effects on their reaction to light. So light fastness testing instruments must also be able to control these environmental factors – to create the relevant conditions for each test and keep them consistent throughout”.

And if the material is going to be used outdoors, the weather – particularly rain – is another important consideration. The testing instruments need a water spray that simulates rainfall, and that can be regulated to reflect the climate of different parts of the world.


Materials that perform poorly in light fastness testing indicate that a product is likely to fade when exposed to light. This may result in product returns or complaints from customers. Therefore, if manufacturers can undertake light fastness testing during R&D, this can provide a warning sign during development.

Measure and control

How do you know when the material has had enough exposure to light? For many years, ‘Blue Wool light fastness reference standards’ have been used to indicate the end of test exposure and for grading purposes. Now it’s becoming common for testers to measure and control the level of irradiance, the test being complete when a certain level of irradiance has been attained. The latter is obviously the more sophisticated technology: in the best systems, a sensor measures the light, and then automatically adjusts the lamp power to keep the light output constant. Both methods have their supporters, so the best testing equipment is that which lets you use both blue wools and irradiance control – individually and in combination.

Who actually does the testing?

Until recently, most manufacturers wanting to run light fastness tests on their materials had to send everything out to specialist laboratories. It has been a complex and expensive process – something definitely best left to the experts. But now, technological advances have led to the development of modern, affordable testing equipment, which is much easier to use. So it’s viable for companies in a range of industries to do the testing themselves.

Perfecting the technology

With many years’ experience in producing testers for all kinds of colour fastness, we saw the emerging need for more accessible, user-friendly light fastness technology, so we developed TruFade, our revolutionary light fastness tester. TruFade, can be used to test the light fastness of textiles and other materials. With its excellent reputation for reliability and simplicity of use, TruFade has proved to be a highly reliable instrument and reference locations can easily be found in the best Independent Labs in the World.

“As with all James Heal instruments, TruFade, incorporating the innovative Solarsens, and the very latest Touch screen technology, provides complete confidence at a competitive price,” adds Peter. “TruFade has many technical advantages – a vertical xenon lamp, with sample holders, which rotate around it ensures consistent sample temperature and even exposure to the light source. The vertical rotating action also means realistic sample interaction with the humid air, reducing test condition variations and producing much repeatable results.”

The ability to accurately control temperature and humidity is important. Testing equipment needs a way of anticipating the effects they can have on each other. TruFade, overcomes these uncertainties, to achieve the desired settings without one factor throwing the other out of balance.

The ‘obvious choice’ for customers

The accuracy, reliability and ease of use makes the TruFade an excellent choice for laboratories, and this is proven through work we have done with the University of Leeds.

Chris Carr, Chair of Textile Technology and Head of the School of Design said, “The School of Design at the University of Leeds has a long history of teaching and research in textile technology, and Colour is core area of expertise and research. When establishing a new state-of-the-art Materials Testing Laboratory recently, we sought the advice of James Heal – with their many years of experience in developing testing instruments for textiles, they were the obvious choice.

Our discussion with the owners at James Heal led to an investment in a comprehensive range of analytical tools that is now a showcase facility for the School and highlights the importance of characterisation of materials performance in the modern textiles industry. One of the key instruments we use to determine colour durability is the TruFade Light Fastness Tester.”

Interested in TruFade? Enquire here

TruFade – Key Features:

  • Solarsens on board irradiance meter
  • Touchscreen
  • Advanced software made simple – just a few clicks to start testing
  • Size – smaller footprint in the laboratory than other rotating light fastness testers
  • Easy to change glassware
  • For ISO testing, 240-270 samples can be tested
  • Pre-loaded standards
  • Xenon Arc Lamp
  • Ducting to avoid heat build up in lab

Benefits to your laboratory:

  • Utmost flexibility at a competitive price
  • Credible – used around the world by independent labs and factories
  • James Heal glassware gives confidence in reliable results which match the industry standard
  • A quiet instrument with a small footprint which can be accessed without ladders or tools making testing more accessible

Probably the biggest advantage of the TruFade light fastness tester is that it easy to use and look after. For example, simple controls and a menu-driven touchscreen interface mean operators require only minimal training. This is something the University of Leeds experienced with their Trufade.

TruFade is an excellent, reliable teaching tool; students can quickly learn to operate the instrument, and its software in particular is easy to understand, guiding the operator to the specified test method. The TruFade system meets ISO and AATCC standards, providing trust in its accuracy of results - a big leap forward for us in understanding the photodegradation, and potential photostabilisation, of coloured materials
Chris Carr - University of Leeds

The ergonomic design allows most maintenance to be done from the front of the machine. Lamps and optical air filters are very easy to replace, so not only is this equipment more affordable to acquire, it’s also cheaper to keep.

Final Thoughts

So, light fastness testing is essential for many types of products. And, although it’s a complicated process, it’s becoming less of a specialist technology. New, easy-to-manage equipment has brought it within the reach of many manufacturers, who no longer have to rely on external testing laboratories. They can carry out the tests themselves whenever they want. Leaving no excuse for faded garments!

For more information, please contact us

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