WO2007095319A2

WO2007095319A2 - Method of accelerated light stability testing and articles

Info

Publication number: WO2007095319A2
Application number: PCT/US2007/003972
Authority: WO
Inventors: Warren D. Ketola; Richard M. Fischer, Jr.
Original assignee: 3M Innovative Properties Company
Priority date: 2006-02-14
Filing date: 2007-02-13
Publication date: 2007-08-23
Also published as: WO2007095319A3

Abstract

Methods of accelerated light stability testing, accelerated light stability testing devices, and illuminators are described. The methods, devices and illuminators described herein are particularly useful for simulating natural sunlight through window glass.

Description

METHOD OF ACCELERATED LIGHT STABILITY TESTING AND ARTICLES

BACKGROUND Often a manufacturer will warranty a product for a specified lifetime. Accelerated light stability testing devices and standard test methods are used by a number of industries to test a product's performance after exposure to (i.e. simulated) solar radiation.

Among the more difficult tasks in the manufacture of accelerated weathering devices is to provide a spectral irradiance of artificial light that matches closely to that of natural sunlight at the earth's surface, i.e. terrestrial sunlight. This is typically accomplished by passing illumination from an artificial light source through one or more optical filters to filter out wavelengths of light that are not present in actual sunlight. By matching or closely approximating the spectral irradiance of natural sunlight, the results of exposure to the accelerated weathering device will more closely approximate effects of real world exposure.

U.S. Patent No. 6,859,309 is directed to an optical filter for use in accelerating weathering device that exhibits certain irradiance ratios that approximate sunlight. A preferred optical filter includes a glass having a lead content of between 0.5% and 50% by weight that is free of visible light absorbing components. In some examples, the filter can be constructed to have a thickness of 0.7 mm to 10 mm. In another aspect, the optical filter is part of an optical filter that may further include an ultraviolet transmissive optical filter. The ultraviolet transmissive optical filter may be constructed from quartz glass and may further include an infrared absorbing coating.

There are many ASTM standard test methods directed to light stability testing. In general, the test methods often refer to filter(s) for "daylight" exposure. These methods are for testing materials intended for outdoor(s). Materials intended for indoor use are often tested with methods that reference a filter(s) for "window glass" exposure to sunlight. Optical filters that approach this specification are commercially available. However, the commercially available optical filters permit short wavelength of light that are not present in natural sunlight that has passed through window glass to strike the test specimen. Such exposure can results in erroneous test results. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the minimum and maximum spectral irradiance of window glass filtered solar radiation from 300 nm to 800 run.

Figure 2 shows the minimum and maximum spectral irradiance of window glass filtered UV solar radiation from 300 nm to 350 nm.

Figure 3 shows the normalized spectral irradiance of commercially available optical filters from 280 nm to 340 nm in comparison to the target of Figure 2:

Figure 4 shows the normalized spectral irradiance of optical filters at various thicknesses from 280 nm to 340 nm in comparison to the target of Figure 2. Figure 5 shows the normalized spectral irradiance of a commercially available optical filter and exemplary optical filter assemblies from 280 nm to 340 nm in comparison to the target Figure 2.

Figure 6 shows the spectral irradiance from 280 nm to 800 nm for the optical filter assemblies of Figure 5 in comparison to the target of Figure 2. Figure 7 shows a side view of an illuminator used within the accelerated weathering device of Figure 1.

Figure 8 shows a cross-section view of the illuminator of Figure 7.

Figure 9 shows a perspective view of an accelerated weathering device.

DETAILED DESCRIPTION

Presently described are methods of accelerated light stability testing, accelerated light stability testing devices, and illuminators. The methods, devices and illuminators described herein are particularly useful for simulating natural sunlight through window glass. The illuminators and devices may also be suitable for other uses. Figure 1 shows the spectral power irradiance from 280 nm to 800 nm of solar radiation filtered by typical window glass. The spectral power distributions shown were derived by multiplying the irradiance values of a standard solar spectrum defined in ASTM G 177 (Standard Tables for Reference Solar Ultraviolet Spectral Distributions: Hemispherical on 37° Tilted Surface, ASTM Book of Standards. VoI 14.04. ASTM International, Philadelphia) by the transmission of typical single strength window glass. The transmission of the single strength window glass used was the maximum and minimum transmission from the set of single strength window glasses studied by the ASTM G3 Committee (Ketola, W., Robbins, J.S., "UV Transmission of Single Strength Window Glass", Accelerated and Outdoor Durability Testing of Organic Materials, ASTM STP 1202, Warren D. Ketola and Douglas Grossman, Eds, American Society for Testing and Materials, Philadelphia, 1993). Figure 2 shows the UV spectral power distribution from 280 nm to 340 run of the window glass filtered solar radiation of Figure 1. The difference between the solar radiation filtered by the minimum transmission glass and the maximum transmission glass serves as a target for filters intended to simulate solar radiation filtered by window glass. Figure 3 shows the normalized spectral irradiance of commercially available optical filters (i.e. Comp A, Comp B, and Comp C) in comparison to the window glass filtered solar radiation target. For each of Figures 3-5, the data was normalized to 0.55 W/m² at 340 nm, which is a commonly used irradiance control point in laboratory accelerated weathering devices. In order to account for noise in measurement of spectral irradiance, the cut-on wavelength is defined as the shortest wavelength where irradiance is at least 0.001 W/m² or where the measured irradiance is the fourth in succession of increasing integer wavelength with increasing irradiance and the minimum irradiance is 0.00002 W/m². These plots describe normalized irradiance in W/m² per nm as a function of wavelength in nanometers. Although Comparative Example C of Figure 3 is close to the maximum spectral irradiance of the target, none of the Comparative Examples fall between the minimum and maximum ultraviolet spectral irradiance of the target.

Figure 4 shows the normalized spectral irradiance of optical filters comprising lead glass that was formed into optical filters having thicknesses of 2 mm, 3 mm, and 5 mm, in comparison to the window glass filtered solar radiation target. This lead glass is commercially available from Schott Glass under the trade designation "WG-320". Although the optical filter having a thickness of 2 mm and 3 mm falls outside of the maximum spectral irradiance of the target, the optical filter having a thickness of greater than 3 mm, (e.g. 5 mm) falls between the minimum and maximum irradiance of the target at wavelengths ranging from 300 nm to about 310 nm.

Figure 5 shows the spectral irradiance of optical filter assemblies of the invention that include a combination of at least two different, filters, in comparison to the window glass filtered solar radiation target, and commercially available optical filter Comp C. Example 1 has the same irradiance as the maximum of the target at a wavelength of about 300 nm. At wavelengths above 300 nm, Example 1 has higher irradiance than the maximum of the target. Example 2 falls between the minimum and maximum irradiance of the target for wavelengths ranging from 300 nm to about 310 nm. Example 2 has the about same spectral irradiance as the maximum of the target for wavelengths greater than 310 nm to about 340 nm. Example 3 falls between the minimum and maximum irradiance of the target for wavelengths ranging from 300 to about 310 nm. At wavelengths from 310 nm to 338 nm, Example 3 is higher irradiance than the maximum of the target.

As evident by Figures 2 and 3, the Applicant has identified optical filters and optical filter assemblies that provide a better simulation of sunlight through window glass at the critical cut-on wavelengths (300-306 nm).

In one embodiment, the optical filter comprises a single glass filter at an appropriate thickness to filter illumination from a light source to approximate solar radiation through window glass. In another embodiment, an optical filter assembly comprising at least two optical filters is employed. In general, irradiance is the radiant power per unit area, typically reported in watts per square meter (W/m²). Two spectral regions are of primary interest for characterizing the optical filter. The first spectral region includes wavelengths up to 300 nm. Ultraviolet radiation less than 300 nm is high(er) energy and may cause rapid and unnatural polymer degradation. Solar ultraviolet radiation that has passed through window glass has very little radiation below 300 nm. The second spectral region includes irradiance at 306 nm and greater. The commercially available filters (as set forth in Figures 1 and 2) as well as the optical filter(s) and filter assemblies described herein provide sufficient irradiance at wavelengths of 306 nm and greater, i.e. at least 0.00003 W/m². However, the optical filter and assemblies of filters described herein advantageously have lower irradiance at wavelengths up to 300 nm, and thus filter out this radiation that is not present in sunlight filtered by window glass. The optical filter and assemblies of filters provide an irradiance of less than 0.00003 W/m² at wavelengths up to 300 nm.

In addition to these two criteria, it is preferred that the ratio of the total irradiance at wavelengths ranging from 400 nm and 700 run in comparison to the total irradiance at wavelengths ranging from 290 nm to 800 nm is at least 0.6 or greater. For example this third ratio may be 0.7 and is typically no greater than about 0.8. This third criterion is typically met by employing a xenon-arc or metal halide light source. The above criteria are preferably met over a large range of power supplied to the light source. For example the light source may provide an irradiance ranging from about 0.3 W/m² to about 1.5 W/m² at 340 nm. The use of higher irradiance than typical with the present filter provides faster test results by reducing the exposure time. The optical filter and each of the filters of the assembly comprise a glass having low concentrations of visible light absorbing components, low concentration of ultraviolet light ("UV") absorbing components, and low concentration of infrared ("IR") absorbing components. In some embodiments, the glass is substantially free of such components. In other embodiments, the optical filters comprise a small amount of such components. For example, the optical filter may contain greater than 2 parts per million of light absorbing components or a concentration of greater than 0.0002% inorganic oxide. In addition the optical filter may further include greater than 2 parts per million UV absorbing component or a concentration of greater than 0.0002% inorganic oxide. Such concentrations can be detected with known laser ablation techniques. The concentration of the total amount of visible light absorbing and optionally UV and/or IR light absorbing components may be greater than 50 parts per million (i.e. elemental absorbing component) or greater than 0.005 wt-% inorganic oxide. The concentration of the total amount of elemental visible light absorbing components is typically less than 0.5 wt-%, less than 0.4 wt-%, less than 0.3 wt-%, less than 0.2 wt-%, or less than 0.1 wt-%. Various visible light absorbing are known including for example Fe₂Oa, C^C^ Co₂O₃, Cu₂O, CuO, MnO, Mn₂Os, V₂O₅,

CeO₂, Sb2θ3, SnO₂, and Nd₂O₃. The presence of visible light absorbing inorganic oxides typically imparts color to glass. Various UV absorbing components are also known including for example Cu₂O, CuO, and Tiθ₂- CuO is also a known IR absorbing component. With the exception of the detectable amount of visible light absorbing and optional

UV light absorbing component, the remainder of the optical filter comprises one or more inorganic oxides that provide a transparent glass. Accordingly, the remainder of the optical filter comprises one or more inorganic oxides that do not absorb visible light and/or UV light. In some embodiments the optical filter comprises at least 40 wt-% and typically no more than 80 wt-% silicon dioxide. The optical filter may also comprise potassium oxide and optionally sodium oxide in concentrations totaling up to about 30 wt- %. The optical filter preferably comprises a lead content ranging from about 0.5% to about 50% wt-%. In some embodiments, such as the exemplified embodiments, the lead content of the glass ranges from about 25% to about 30% wt-%.

An exemplary glass composition and filter may comprise the following inorganic oxides.

*In the glasses, some of the metal oxides could be in different oxidation forms (for instance As could be in AS₂O₃ or As₂Os).

In one embodiment, the optical filter comprises a single lead glass filter having a thickness of at least 3 mm, preferably greater than 3 mm (e.g. 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm) and more preferably at least about 3.5 mm. The single glass filter typically has a thickness of less than 10 mm, and more typically less than 6 mm. These thicknesses are based on glass having a lead content of about 30 wt-%. Accordingly, the thickness of the glass can vary depending on the amount of lead in the optical filter. For example, for embodiments wherein the glass has a lead content of approximately 50 wt-% by weight, the filter may have a considerably smaller thickness of approximately 2 mm. Alternatively, if the lead content of the glass is only 5 wt-%, the thickness may be greater than 10 mm.

In another embodiment, an optical filter assembly is employed having at least two optical filters operably coupled.

Figure 4 shows one example of an illuminator 38. The illuminator 38 includes a pair of end caps 40 that couple and retain the light source 42. Plug 44 mates with a conductor in the illumination assembly 36 to provide power to the light source 42. The light source 42 is surrounded by optical filter assembly 46. In the example shown, the optical filter assembly 46 includes two optical filters, for example inner filter 52 and outer filter 54. A coolant 50 flows through the illuminator 38 to control and maintain the temperature of the illuminator 38. Light source 42 includes a lamp having spectral emissions at least in the range of 200 run to 700 nm. Examples of known light sources suitable for use in simulation of sunlight through window glass testing include carbon-arc lamps, xenon-arc lamps, metal halide lamps, and the like. In the examples shown, the light source 42 is a xenon-arc lamp and the fluid coolant 50 is water.

Figure 5 shows a cross-section of the optical filter assembly 46 taken along line 3- 3 of Figure 4. The optical filters 52 and 54 are shown having a circular cross-section indicating that the filter assembly 46 is cylindrical. Other curvilinear or rectilinear shapes for the optical filters 52, 54 are contemplated. Coolant 50 flows in a first direction along the length of the illuminator 38 between the light source 42 and the inner filter 52. Coolant 50 flows in the opposite direction between the inner filter 52 and the outer filter 54. Other systems can include a cooling water inlet on one end and an outlet on the other. At least one filter (e.g. inner filter) of the assembly may provide irradiance ratios that approximate terrestrial sunlight. Suitable filters are described in Issued U.S. Patent Nos. 6,859,309 and 6,906,857, Pending U.S. Patent Application Publication No. 2004/0233520 and Pending U.S. Patent Application Serial No. 11/141231, filed May 31, 2005, all of which are incorporated herein by reference. Illumination passed through the first optical filter has a first ratio of total irradiance for wavelengths shorter than 290 nm to total irradiance for wavelengths ranging from 300 nm to 400 nm of less than 2.0 x 10^"6, a second ratio of irradiance at 310 nm to total irradiance for wavelengths ranging from 300 nm to 400 nm of at least 1.2 x 10^"3, and a third ratio of total irradiance at wavelengths ranging from 400 run to 700 nm to total irradiance at wavelengths ranging from 290 nm to 800 nm of at least 0.6. Total irradiance is the sum of the irradiance measured for each integer wavelength over a given range. A suitable method for determining total irradiance is to make measurements of irradiance at 2 nm increments, then add up the irradiance at each measured wavelength and multiply the resulting sum by 2. To calculate the first total irradiance, the sum of the irradiance measured from 250 nm to 288 nm at 2 nm increments is multiplied by 2. To calculate the second total irradiance, the sum of the irradiance measured from 300 nm to 400 nm at 2 nm increments is multiplied by 2. The first filter has a cut-on wavelength typically ranging from 290 nm to 300 nm. The cut-on wavelength is defined as the shortest wavelength where irradiance is at least 0.001 W/m² when tested with a xenon-arc or metal halide light source. Test methods for determining the cut-on wavelength are susceptible to noise. In order to account for noise, the cut-on wavelength can also be defined as the wavelength where the measured irradiance is the fourth in succession of increasing integer wavelength with increasing irradiance and the minimum irradiance is 0.00002 W/m².

The second filter of the assembly is typically soda lime window glass, other glass, or other transparent material through which sunlight is commonly filtered. Various glass types are used for windows of architectural structures including homes and buildings. The various glasses provide a variety of transmission properties in the ultraviolet, visible, and infra-red portions of the terrestrial solar spectrum. A comprehensive library of glazings commonly applied to architectural glasses is maintained by the Building and Environmental Technologies Divisions of Lawrence-Berkley Laboratories and is accessible via the internet at http://windows.lbl.gov/Default.htm. Other types of window glass are utilized in the transportation industry for automobiles, trucks, buses, trains, etc. Polymer-based light transmissible (e.g. substantially transparent materials) such as PMMA and polycarbonate are also used as window materials.

In one embodiment, the first filter may comprise a lead glass filter; whereas the outer filter comprises soda lime glass. The lead glass filter may for example have a lead content of about 30 wt-% and a thickness of greater than 3 mm. However, the thickness can vary depending on the concentration of lead as previously described. Unlike quartz that consists of pure silica, soda lime glass consists of a uniformly dispersed mixture of about 75% silica, 20% soda ash, and 5% lime. The thickness of the soda lime glass filter is typically at least 0.5 mm, and preferably at least 1 mm. Further, the thickness of the soda lime glass filter is typically no greater than 5 mm.

The composition of soda lime glass can vary to some extent depending on the ^'manufacturer. Such compositional variation in turn affects the transmission properties. Lead glass filters such as prepared from WG-320 tend to exhibit consistent transmission properties as a function of filter thickness. For this reason it is generally preferred to first select a soda lime glass of an appropriate thickness (e.g. 1 to 2 mm) and then select the thickness of the WG-320 filter such that the combination falls within the target, particularly at wavelengths from 300 nm to 310 nm. Some suitable combinations that are expected to meet such target are as follows:

Average Thickness of Average Thickness of

Soda Lime Filter Prepared from Filter Prepared from

"AR-GLAS" available from Schott "WG-320"

2 mm 1 mm

1.4 mm 2 mm

0.7 mm 3.2 mm

0.3 mm 4 mm

Other variations would be readily construed by one of ordinary skill in the art. For example, the illuminator may have various other shapes and sizes and/or the optical filters in a filter assembly may be adjacent to or touching one (e.g. multilayer coextruded filter) another rather than spaced apart. In order to improve the durability of the optical filter it is preferred that the optical filter proximate the light source comprises an opaque peripheral portion as described in

Published U.S. Patent Application No. 2004/0246745; incorporated herein by reference.

A fitting is typically attached to the opaque peripheral portion and a polymeric material

(e.g. adhesive) is disposed between the fitting and the opaque peripheral portion. The opaque peripheral portion shields the polymeric material from the illumination thereby reducing the rate of degradation. The optical filter and filter assembly described herein can be adapted to be employed in various known laboratory accelerated weathering test chamber devices such as available from Q-panel Lab Products, Cleveland, OH under the trade designations "Model Q-Sun XeI and Xe3" and from Atlas Material Testing Technology LLC, Chicago, IL Suntest under the trade designations "CPS/CPS+", "XLS/XLS+", and "XXL₉XXL+", "Ci 35/65", ¹¹Ci 3000/4000/5000", "Xenotest 150V, and "Xenotest Alpha and Beta". Suga Test Instruments Co., Ltd, Tokyo, JP also distributes weathering devices.

Figure 6 is a representative accelerated weathering device 20 suitable for conducting the light stability testing described herein. The accelerated weathering device 20 includes a weathering chamber 22. Inside the weathering chamber 22 is a weathering fixture 24 adapted to hold a number of product samples (not shown) for testing. Exposure parameters such as humidity, condensation, temperature, and irradiance are input through user-interface 26. Mist generators 28 typically provide atomized water into the weathering chamber 22. Humidity within the chamber is measured via humidity sensor 30. Heater 32 generates heat within the chamber 22. Heat is measured with a temperature sensor 34. Signals received from the sensors 30, 34 are used to control or maintain the temperature and moisture stresses within the chamber 22. The weathering chamber 22 also includes an illumination assembly 36 that includes illuminator 38. The illumination assembly 36 provides and controls irradiance and works to cool illuminator 38. In the example shown, the illuminator 38 is disposed near the center of the weathering fixture 24 to provide irradiance to the product samples.

Use of such. accelerated weathering devices generally includes providing at least one product sample proximate an illuminator in an accelerated weather device and radiating the product sample with the illuminator. Any product can be subjected to accelerated weathering. Products that are subject to exposure to sunlight through window glass environments are most commonly tested including for example paint, varnish, protective coatings, plastics, textiles (e.g. upholstery, clothing), (e.g. digital printed) photographs, carpets, window treatments (e.g. curtains and blinds), window display materials, architectural ornaments, tapes, sealants, medication, adhesives, and other articles found or used inside a building or vehicle. Generally one or more product performance tests are conducted prior to and after various durations of exposure. Representative tests include, for example, gloss, color shift, adhesion (cross hatch and peel strength), tensile and elongation, haze, chemical changes detected by a range of analytical techniques (IR, UV/Visible spectrometry, etc.), visual appearance (cracking, delamination, adhesion failure, shrinkage), as well as any loss of intended function.

Objects and advantages of the invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in the examples, as well as other conditions and details, should not be construed to unduly limit the invention. All percentages and ratios herein are by weight unless otherwise specified.

Examples

Samples of glass were prepared into tubes having 1 mm, 2 mm, 3 mm and 5 mm cross sections by Pegasus Glassworks Inc., Sturbridge, MA. Each tube was cut to a length of 30 cm.

Spectral irradiance measurements in the weathering devices were made with a spectroradiometer commercially available from Optronics (Orlando, Florida) under the trade designation OL754 with OL754-PMT optics head and OL752S integrating sphere. The spectroradiometer was calibrated with a standard tungsten halogen lamp (Optronics OL752-10E or OL752-10J) with calibration traceable to National Institute for Standards and Technology (NIST). Spectral irradiance measurements were made from 250 to 400 nm at 2 nm increments or from 250 to 800 nm at 2 run increments.

Spectral irradiance data in Figures 3-5 was normalized to 0.55 W/m² at 340 nm, which is a commonly used irradiance control point in laboratory accelerated weathering devices. The plot describes normalized irradiance in W/m² per nm as a function of wavelength in nm.

Example Light Inner filter Outer filter Irradianc Irradiance at source e up to 306 nm

300 nm

Comp. A Xenon-arc 3.3 mm Soda- 1 mm 0.0074 0.0177

(a) lime (Atlas part # Borosilicate

20313000) (Atlas part #

20313200)

Comp. B Xenon-arc 3 mm Q-Panel, 0.0017 0.0124

(b) Part No.

X- 10214-K (c)

Comp. C 3 mm Q-Panel 0.00005 0.0023

Part No. X- 10266-K

(C)

Xenon arc 1 mm soda lime 3.2 mm 0.00001 0.0031

(a) ("AR-GLAS", WG-320

Schott, North

America,

Elmsford, NY)

" " 1 mm soda lime + 3.2 mm 0.000003 0.0006

1.5 mm soda-lime WG-320 middle filter (d)

" " 1 mm soda lime 2 mm WG 0.00000 0.0005

320 and 3 mm WG-

320 a - water-cooled xenon arc — Ci 5000 mfg by Atlas-MTS Chicago, IL b - air-cooled xenon arc — Q-Sun Xe-3 mfg by Q-Panel Lab Products, Cleveland, OH c — air-cooled xenon arcs typical use single flat filter panes d — 1.5 mm soda-lime filter fits concentrically over the 1 mm soda-lime filter with a gap of less than 1 mm between

Various modifications and combinations of the embodiments disclosed will be apparent to those skilled in the art, and those modifications are intended to be within the scope of the invention as defined in the appended claims.

Claims

WHAT IS CLAIMED:

1. A method of light stability testing comprising: providing at least one product sample proximate an illuminator in an accelerated weather device, the illuminator comprising a light source and one or more optical filters disposed proximate the light source; radiating the product sample with the illuminator for simulation of sunlight through window glass; wherein the optical filter provides i) a total irradiance of less than 0.00003 at wavelengths up to 300 nm; ii) a total irradiance of greater than 0.00003 at a wavelength of 306 nm.

2. The method of claim 1 wherein the light stability testing is accelerated in comparison to actual exposure through window glass testing.

3. The method of claim 1 wherein the optical filter comprises a glass having a lead content of about 0.5% to about 50% by weight.

4. The method of claim 3 wherein the glass has a lead content of about 25% to about 35% by weight.

5. The method of claim 4 wherein the optical filter has a thickness ranging from greater than 3 mm to about 10 mm.

6. The method- of claim 1 wherein the optical filter comprises an assembly including lead glass optical filter operably coupled to a soda lime glass filter.

7. The method of claim 6 wherein the lead glass filter has a lead content of about 25% to about 35% by weight.

8. The method of claim 7 wherein the lead optical filter comprises one or more filters having a total thickness of less than 3 mm.

9. The method of claim 6 wherein the soda lime glass filter comprises one or more filters having a total thickness ranging from about 0.5 mm to about 5 mm.

10. The method of claim 1 wherein the illumination from the light source includes a spectral component of at least 250 run to 800 nm.

11. The method of claim 1 wherein the light source is selected from the group consisting of carbon-arc lamps, xenon-arc lamps, and metal halide lamps.

12. The method of claim 1 wherein the product sample is selected from the group consisting of paints, varnishes, protective coatings, plastics, textiles, carpets, photographs, window treatments, window display materials, architectural ornaments, tapes, sealants, medications, adhesives, and water proofing treatments.

13. The method of claim 1 further comprising testing at least one product performance attribute after radiating the sample.

14. An accelerated weathering device comprising: a weathering fixture adapted to hold at least one product sample; an illuminator disposed proximate to the weathering fixture wherein the illuminator comprises a light source and a first and second optical filter disposed proximate to the light source, wherein illumination passed through the first optical filter has a first ratio of total irradiance for wavelengths shorter than 290 nm to total irradiance for wavelengths ranging from 300 nm to 400 nm of less than 2.0 x 10^"6, a second ratio of irradiance at 310 nm to total irradiance for wavelengths ranging from 300 nm to 400 nm of at least 1.2 x 10^"3, and a third ratio of total irradiance at wavelengths ranging from 400 nm to 700 nm to total irradiance at wavelengths ranging from 290 nm to 800 nm of at least 0.6; and the second filter comprising window glass or a light transmissive window material.

15. The device of claim 14 wherein the first filter is a lead glass filter.

16. The device of claim 14 wherein the second filter is a soda lime glass filter.

17. The device of claim 1 wherein illumination passed through the first and second filters provides i) a total irradiance of less than 0.00003 at wavelengths up to 300 nm; and ii) a total irradiance of greater than 0.00003 at a wavelength of 306 nm.

18. An illuminator comprising a light source and a first and second optical filter disposed proximate the light source wherein illumination passed through the first optical filter has a first ratio of total irradiance for wavelengths shorter than 290 nm to total irradiance for wavelengths ranging from 300 nm to 400 nm of less than 2.0 x 10^"6, a second ratio of irradiance at 310 nm to total irradiance for wavelengths ranging from 300 nm to 400 nm of at least 1.2 x 10^"3, and a third ratio of total irradiance at wavelengths ranging from 400 nm to 700 nm to total irradiance at wavelengths ranging from 290 nm to 800 nm of at least 0.6; and the second filter comprising window glass or a light transmissive window material.

19. The illuminator of claim 18 wherein the first filter is a lead glass filter.

20. The illuminator of claim 18 wherein the second filter is a soda lime glass filter.

21. The illuminator of claim 18 wherein illumination passed through the first and second filters provides i) a total irradiance of less than 0.00003 at wavelengths up to 300 nm; and ii) a total irradiance of greater than 0.00003 at a wavelength of 306 nm.