Over Exposed: Protect packaged products from light

Exposure of packaged products to both natural sunlight and artificial light is on the rise. Extended distribution channels mean many products end up in unintended environments such as outdoor stalls and exposed shelving areas in countries where much more of life occurs outdoors than is the norm for North America. Initiatives to use natural light in stores are resulting in more sunlight being added to the typical in-store lighting mix, which already consists of significant ultraviolet (UV) components.

It's well known that the shorter wavelengths of UV light are responsible for most of the material damage due to light. However, visible light cannot be ignored, as many nutritional, flavor, and colored components are very sensitive to wavelengths in the visible range as well.

Shelf life of consumer goods generally is short enough that we have not had to worry much about exposure to light energy. However, there are many products that may find themselves stored from season to season and may spend substantial time exposed to sunlight or lighting in warehouses or stores.

There are many examples of products that have failed due to exposure to light in the distribution network. Figure 1 shows one dramatic example.

Products that fail due to light exposure

  • An attractively colored blue mouthwash was found to gradually turn a sickly shade of green after only a few hours of exposure to certain types of in-store lighting. Fortunately, this was observed early as different lots of material reached the store shelves to be placed next to older inventory that showed early signs of this color decay.
  • Many of the non-cola drinks contain artificial color components. The producers of these products have learned to do lightfastness studies before market introductions. Cola is subject to photodegradation as well.
  • A manufacturer of a fabric deodorizer discovered that when the bottle of product was allowed to remain in vehicles with exposure to light, the product changed from deodorizer to a very malodorous aerosol.
  • Certain types of fluorescent store lighting cause deterioration of whole milk products in transparent or translucent glass or HDPE bottles.
  • In addition to product photodegradation, print fading on the package is a common problem in cases where non-stable inks are used. High chroma organic pigments and dyes are much more susceptible to light than some of the older systems. Most stable of all is the oldest: carbon black. Increasing use of inkjet printing will mean that greater care will need to be taken so that the graphics do not change color faster than the anticipated shelf life of the product.

Finding Solutions

So what is to be done? The first step is to determine whether there could be a problem of poor resistance to light energy for some specific product. The second step is to determine how to protect against a negative outcome.

It is obvious the best approach would be to test the actual product/package/label in the environment anticipated for its use for the maximum time of expected exposure. This has some obvious drawbacks, both in terms of the time it will take and, more importantly, in anticipating all of the different potential exposures possible.

Therefore, we usually resort to an FMEA (Failure Mode and Effects Analysis) to determine a best estimate of possible failure modes and the cost balance of their occurrence. From this we can determine the worst exposure that must be overcome.

Note this does not mean that we plan against every exigency. We need to deal only with those that will have a significant cost or image impact. With this analysis in hand, we have access to laboratory testing options.

Two Principal Methods

As mentioned previously, the best test in every case is to duplicate the end-use exposure and place the package in that environment for as long as exposure is expected to last. The next best approach, however, is to use existing instrumentation to attempt a close parallel to anticipated conditions and then expose the package accordingly.

The two principal methods currently available are instruments based on xenon arc light sources or, alternatively, instruments based on UV-producing fluorescent lamps.

Methods are available to use the light from xenon arc lamps to duplicate, with appropriate filters, either indoor or outdoor light. They can duplicate, with reasonable accuracy, outdoor sunlight or, alternatively, sunlight as viewed through window glass or other screening elements.

The filtered xenon arc lamp provides a full spectrum exposure, including the visible and infrared wavelengths. It is known that many products as well as the colorants used in packaging and inks are sensitive to visible light as well as UV, so testing with a full-spectrum xenon arc light source provides the greatest range of exposure conditions to both outdoor and glass-filtered sunlight as well as indoor artificial light. However, if the UV wavelengths are of particular concern, preliminary screening tests with fluorescent devices using UVA lamps may be an economical first step.

The second method uses controlled irradiation fluorescent lamps to provide measured quantities of a narrow spectrum of UV light. Because the UV wavelengths are those that do most of the damage to most products, using this method often is sufficient. We strongly recommend that users of fluorescent UV devices employ the appropriate bulbs that mimic the short wavelength UV that occurs in the intended end-use application.

Figure 2 and Figure 3 are examples of these two instrument types. The xenon instrument (Figure 2) has air-cooled lamps, an exposure surface of approximately 400 sq in., and irradiance, temperature, and humidity control. Fluorescent instruments, like the one shown in Figure 3, also are widely used and provide temperature/humidity control as well as controlled irradiation within fixed, though truncated, parameters and exposure area of approximately 1,000 sq in.

Barrier Additives

Protecting against the invasion of spectral light into products in non-opaque packages can be undertaken by incorporating a number of different UV-absorbing additives into the polymeric packaging materials. It is important to note, however, that simple inclusion of these materials into a thin film within a package usually is not sufficient to provide the appropriate energy barrier. Some thickness of absorbing medium is usually required, as stipulated in the Beer-Lambert Law, and a sufficient concentration of the UV absorber/inhibitor as well.

In addition, although blocking the UV wavelengths will reduce the majority of product degradation, visible light is involved in many of the color and flavor changes that occur in foods and other products. Permitting the transmission of visible light is the compromise necessary to provide product visibility.

Many of the traditional UV absorbers will not pass FDA scrutiny for food applications. There are a few, such as some of the triazines, that will pass FDA scrutiny currently. Consequently, there is significant research underway to find materials more readily acceptable in food packaging. Work with zinc oxides, nanoparticles, and other non-toxic chemistries is being carried out by such organizations as Virginia Technical Univ., Ciba Corp., and Advanced Nanotechnologies of Australia.

In conclusion, exposure of packaged products to various forms of light is becoming more and more prevalent and an important variable to be considered when designing new packaging. Protection of packaged product from light is assuming a place alongside moisture and gas barrier as a requirement of many converted materials.

David P. Dumbleton is a senior consultant with Atlas Material Testing Technology, Chicago, IL. He has more than 30 years of experience in the converting, packaging, and raw materials industries. Contact him at This email address is being protected from spambots. You need JavaScript enabled to view it..

Oscar Cordo is manager, technical standards, with Atlas Material Testing Technology. He is an active participating member of ASTM, SAE, AATCC, and other committees related to weathering and durability. Contact him at This email address is being protected from spambots. You need JavaScript enabled to view it..

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