UV Testing

UV Testing

Micom offers UV testing services as part of its accelerated aging testing. UV sun exposure can be done through direct exposure i.e.: outdoor exposure or the impact of sun exposure through glass i.e.: indoor exposure.  There are many test methods and two main practices for this important type of ageing process. Among others,  Micom offers UV testing services to the following test methods and practices as well as many others:

  • ASTM G154 “Standard Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials”
  • ASTM G155 “Standard Practice for Operating Xenon Arc Light Apparatus for Exposure of Non-Metallic Materials”
  • ASTM D2565 “Standard Practice for Xenon-Arc Exposure of Plastics Intended for Outdoor Applications”
  • ASTM D5208 “Standard Practice for Fluorescent Ultraviolet (UV) Exposure of Photodegradable Plastics”
  • ASTM D5894 “Standard Practice for Cyclic Salt Fog/UV Exposure of Painted Metal, (Alternating Exposures in a Fog/Dry Cabinet and a UV/Condensation Cabinet)”
  • ASTM D6695 “Standard Practice for Xenon-Arc Exposures of Paint and Related Coatings”
  • – ISO 4892-2 “Plastics — Methods of exposure to laboratory light sources — Part 2: Xenon-arc lamps”
  • SAE J2412 “Accelerated Exposure of Automotive Interior Trim Components Using a Controlled Irradiance Xenon-Arc Apparatus”
  • SAE J2527 “Performance Based Standard for Accelerated Exposure of Automotive Exterior Materials Using a Controlled Irradiance Xenon-Arc Apparatus”
  • – ASTM D4329 “Standard Practice for Fluorescent Ultraviolet (UV) Lamp Apparatus Exposure of Plastics”
  • – ASTM D4459 “Standard Practice for Xenon-Arc Exposure of Plastics Intended for Indoor Applications”

For a more elaborate list of available test methods, please see: Test methods requiring the use of a QUV and Test methods requiring the use of a Xenon Arc Tester.

Use and factors to be considered:

The ultimate goal is of UV testing is to “compress time” so that we know how a product will react to sunlight as it gets exposed more and more.  To do so, we want to simulate the sun on an accelerated basis; this process is called “Accelerated weathering”.  Just like for any other accelerated aging process, the goal is to have the best simulation possible with the fastest aging rate possible while not inducing reactions that would not occur under normal exposure conditions.  The two prevalent UV aging type of equipment used nowadays are: Xenon arc  and Fluorescent light. Each technique has pros and cons and each of them can also be used with a broad variety of test conditions that can drastically change the test outcome. Xenon arc testing is mainly used to assess color/appearance changes over time as a result of indoor/outdoor exposure to UV light either directly from the sun or through glass (indoor conditions). There is no fix algorithm that allows to predict accurately what is the actual ageing rate also called “time compression factor ”.  However, with Xenon arc, reasonable assumptions can be made to at least approximate orders of magnitude. For more information on time compression factor and the test parameters required see:

Fluorescent light accelerated weathering testing is mainly used to assess mechanical properties retention through exposure. This technique is used for comparison/certification purposes. However, scientific literature is clear that this technique, despite its uses, is a poor time predictor. For more information on this test method please see: ASTM G-154.

Micom also offers UVc exposure  for surfaces used in healthcare environments.  UVc exposure is often used as a sanitation process in healthcare environments.

Post UV testing optical measurements:

What is of interest to most of our customers requiring UV testing is not so much how the exposed samples look upon test completion as much as how different from the unexposed sample they look.

Typically gloss and color measurements a taken at different exposure intervals until the total planned exposure duration is completed.  In some cases, even is the color and gloss are the same we can see  significant discrepancies between samples exposed at different time intervals.  This can be explained by the fact that the human eye sees more than gloss and color.

Eye

There are three types of reflections; specular, scattered, diffused.  A good example of a high specular reflection object would be a mirror or a perfectly polished metal.  Scattered reflection:  most materials fall into that category; most of the light is reflected in the specular angle but surface defects will scatter the light creating a bell curve deflection. The bell curve shape will depend on the micro-topography of the surface.  A good example of diffuse reflection would be white paper.

Standard Gloss meters (ASTM D523) measures the « shininess » / Brightness (quantity of the light directly reflected from the surface).  However, in comparing gloss measurements with what our eye sees, it is important to be aware that the human eye evaluates much more than the shininess of the surface.  Simply put; two products with a similar gloss can look very different.

This is explained by the fact that whereas a gloss meter can only measure the specular reflection at a specific angle, the eye can see the light scattering as well i.e. a diffuse reflection.

Reflection

Nowadays, equipment with light sensor arrays can take measurements that mimic the light reflection on the human eyes cones.  These new sensors allow us to measure additional parameters:

  • – Haze
  • – RIQ (Reflected Image Quality)
  • – DOI (Distinctness of Image)
  • – RSpec(Smoothness quantification)

Haze is produced by imperfections/irregularities on the surface  that affect the light distribution around the specular angle. Haze is sometimes called « gloss haze » as both are related. Haze is actually the sum of the gloss around the specular angle (-3° to -1 ° and +1 ° to +3 °) and is sometimes compared to « turbidity ».

DOI (Distinctness Of Image) measures how clearly an image appears on a reflective surface. A low DOI indicates  image distorsion amd a perfect mirror has a DOI of 100.

RIQ Reflected Image Quality is an improved version of the DOI.  It provides a better response to orange peel effects on a wider range of materials and textures.

Rspec is the Peak Specular Reflectance  at ± 0.0991° around the specular angle. This very precise measurement quantifies the surface texture as any wave or ripple on the surface will create light diffraction and therefore affect the «light response ».  For a perfectly smooth surface, the RSpec value will be equal to the gloss value.

10 things to know for a successful UV testing project

UV testing is often required on carbon based materials and coatings as they react with UV radiations to which they are exposed either because of sunlight or artificial light exposure.  UV aging can cause a wide range of damaged from color fading to depletion of material resistance depending on the radiation source, the intensity and other contributing environmental factors.  Important factors to consider for getting the right answers while requiring UV testing are:

        1. 1.  UV source
          1. a.  Sun?
          2. b.  Artificial light?
        2. 2.  Indoor or outdoor exposure?
        3. 3.  Ambient temperature? Aggravating factor.
        4. 4.  Ambient relative humidity? Aggravating factor.
        5. 5.  Rain cycle? Erosion & cooling effect promoting aging.
        6. 6.  Dark cycle? In some cases this will promote chemical reactions that would not happen otherwise.
        7. 7.  Sample size; shape, thickness
        8. 8.  Which undesirable impacts do you expect and are you trying to prevent? Color change or loss of mechanical properties might dictate the use of a different test protocol.
        9. 9.  Duration of the predictable real life exposure.
        10. 10. Do you need progressive sampling/measurements on your samples?  This will limit your testing costs should the materials you are testing are not performing as expected.

How to choose between ASTM 154 and ASTM 155 UV Tests?

The following infographic and decision tree will help you understand when to choose ASTM 154 and when to choose ASTM G155 UV tests.

UV Testing Infographic, how to choose between ASTM G154 and ASTM G155

Should you need help, our experts will be happy to recommend the proper test conditions: contact us.

Other related test methods:

For additional test methods related to UV testing please see: Plastics, Surface coatings or ASTM.

We also invite you to download our PDF on the true color measurement: What is the difference between the “true” color of an item and its “perceived” color (by the human eye)?

 

UV Testing Frequently Asked Questions

Here are 10 most frequently asked questions about UV Testing:

1. What is the acceleration factor of a Xenon Arc or UV test?

For decades, weathering experts have tried to find that magic number, but there is no such magic number.  No matter how the question is formulated, the answer is always the same: “It depends!” It depends for one simple reason: Mother Nature is not as reliable as lab equipment! Read more.

2. I want to perform an accelerated light aging test, what type of machine should I use?

There are 3 main kinds of machines available: Carbon Arc, Xenon Arc and Fluorescent UV testers. Carbon Arc is the oldest technology (developed in the 1930’s) for accelerated aging and is now regarded as inaccurate and outdated. Read more.

3. What is the difference between Xenon Arc and Fluorescent (UV) testing?

Xenon Arc tester is the best sun simulator available today. By using the right combination of filters we can simulate sunlight very precisely (wavelength range and relative amplitude of each wavelength) for either outdoor or indoor conditions. Read more.

4. What is the correlation between Xenon Arc and Fluorescent (UV) testing?

There is no correlation between the 2 types of exposures because they have different emission spectrums and ambient parameters (i.e.: one has condensation cycles, simulating dew, the other one has rain cycles). Read more.

5. What is the difference between Xenon Arc and Carbon Arc testing?

Carbon Arc testers were introduced in the 1930’s, they were the best available sun simulators at the time. Carbon Arc testers were pioneers in the technology of accelerated aging. That technology is still called up in some standards even though there is nowadays a much better technology: Xenon Arc. Read more.

6. What is the correlation between Xenon Arc and Carbon Arc testing?

There is no correlation between the 2 types of exposures because they have different emission spectrums. Furthermore, Carbon Arc emission spectrum is a poor simulation of the sun spectrum because of 2 major mismatches. Read more.

7. What do L*.a*.b*. values and DE represent?

L*.a*.b*. coordinates refer to the coordinates of the color in the CIELAB 76 sphere. It is actually a three-dimensional space where the L* axis represents the “lightness” of the color (Black to white), a* is the green-red axis and b* is the blue-yellow axis. Read more.

8. What is the difference between SCI and SCE color measurements?

SCI (Specular Component Included) measures the true color of an item, ALL the reflected light is captured, regardless of the reflection angle (specular, scattered or diffuse). Read more.

9. I’d like to have intermediate measurements taken, what intervals should I choose?

Aging is usually a non-linear process, therefore we suggest the following intervals in order to catch early failures or changes. Read more.

10. What is the difference between the terms Sample and Specimen?

In the Testing Industry, a sample is a type of product and a specimen is an individual unit. In other words, specimens are identical “items” and samples are different “items”. Read more.

We invite you to learn more about five other most frequently asked questions about UV Testing.