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What is Light Fastness Testing?
2019/07/18
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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.
Commercial benefit：
At a commercial level, light fastness testing gives manufacturers confidence in their products. 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.
Experiment and test：
Light Fastness Testing is a good way for brands and product designers to 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 for most materials this can take months or even years – and how many R&D departments can afford to wait that long?
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.
Xenon Long Arc Radiation：
This is the only way to reliably reproduce the sunlight spectrum, and it involves using different optical filters to replicate specific light conditions.
For instance; 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: Temperature & Humidity：
“It’s not as simple as putting a material under a certain type of light and observing how it performs,” explains Peter Goodwin, Technical Specialist. “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”.
Impact of Weathering：
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.
Performance and R&D：
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.
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