"I had it displayed in a place where direct sunlight didn't hit it, but somehow the color changed over time."
I've heard such comments before.
Various factors contribute to the fading of art posters. Among these, we focused on "ultraviolet rays," which are relatively easy to counteract indoors.
How does the fading of a piece change depending on the front material of the frame? How much attention should be paid to UV rays entering through windows?
Let's organize this based on experimental data.
Ultraviolet rays are one of the major causes of fading
The fading of art posters is not caused solely by ultraviolet rays. It progresses due to a combination of multiple factors, including visible light, heat, humidity, oxygen, and the quality of the paper and ink.
Here, "visible light" refers to the light from sunlight and artificial lighting that we perceive as brightness and color. Technically, it is called "visible light."
Among these, ultraviolet light is relatively easy to counteract indoors.
According to the document referenced, the comparative values for the amount of UV light generated by lighting are: incandescent bulbs at 0.4, fluorescent lamps at 0.1, and LED lighting at approximately 0.002, when direct sunlight on a clear day is taken as 100.
Incandescent and fluorescent lamps do contain UV rays, but they are very small compared to sunlight. LED lighting has an even smaller value.
However, these are not absolute values that apply to all lighting fixtures. The impact on the artwork varies depending on the type of bulb or lighting fixture, the performance of each product, the distance to the artwork, the brightness of the light, and the duration of illumination.
General white LED lighting is said to contain almost no UV or infrared rays, with most of its light falling within the visible spectrum. Therefore, LED lighting is more suitable than incandescent or fluorescent lamps for suppressing color fading due to UV rays.
Nevertheless, LED lighting does not completely prevent fading. Since visible light also contributes to the deterioration of artwork, it is safer to avoid exposing the artwork to strong light from a close distance for extended periods.
The rate of fading changes depending on the front material of the frame
Glass, acrylic, and PET sheets are primarily used for the front material of picture frames. How do these materials affect the fading of artwork?
Yasui Shoten, a company specializing in frames and framing supplies, commissioned the Tokyo Metropolitan Industrial Technology Research Institute to conduct a test to investigate color changes when exposed to artificially strong light. This is officially known as a "xenon arc lamp accelerated lightfastness test."
A xenon arc lamp is a test lamp that reproduces strong light similar in nature to sunlight. By exposing materials to this light for a certain period, the tendency of fading and yellowing that occurs over long periods of light exposure can be investigated in a relatively short time.
The test duration was 300 hours. Six patterns were prepared: glass, acrylic, UV-cut acrylic, museum acrylic, PET sheet, and no surface protection, and the fading of printed matter and the yellowing of the sheet itself were compared.
・Ease of fading of printed material (artwork side)
No surface protection ＞ Glass ＞ PET sheet ＞ Acrylic ≧ UV-cut acrylic ≧ Museum acrylic
・Ease of yellowing of the sheet itself
PET sheet ＞ Acrylic ≧ UV-cut acrylic ＞ Museum acrylic ≧ Glass
In terms of protecting printed materials, general acrylic, UV-cut acrylic, and museum acrylic all showed less fading than glass or PET sheets. On the other hand, the sheets themselves were more prone to yellowing than glass.
In other words, "the front material itself being resistant to change" and "protecting the artwork inside" are not necessarily the same thing.
General clear float glass also has a certain UV-cutting effect. As described later, the ratio is about 30% depending on the thickness. However, in this test, the printed material faded more with acrylic-based front materials.
PET sheet as an option
Our shop uses PET sheets for the front material of frames.
PET sheets are characterized by high transparency, lightness, and flexibility. Compared to glass and even rigid acrylic sheets, they are less prone to cracking from bending or dropping. Moreover, since they do not contain chlorine, if incinerated properly, they are less likely to generate harmful chlorine-based gases.
On the other hand, in terms of preventing fading, the test we referenced showed an intermediate result: less fading than glass but slightly more than acrylic.
The reason we still choose PET sheets is that we prioritize the balance of fade resistance, lightness, shatter resistance, ease of handling, and cost.
Our aim is for customers to casually display art posters in their daily lives and swap them out according to the season or their mood. We believe PET sheets are suitable for this kind of use.
UV protection even by the window
In addition to the front material of the frame, UV protection can also be implemented at the windows of the room where the artwork is displayed.
"Float glass" is widely used in ordinary windows. It refers to a smooth, distortion-free transparent sheet of glass made by pouring molten glass onto molten metal.
Float glass is used in single-pane windows and as the glass component in insulated glazing units.
Depending on its thickness, it cuts approximately 30% of UV radiation. For reference, manufacturer data shows values of about 27% for 3mm, 31% for 4mm, and 35% for 5mm.
On the other hand, "Low-E insulated glass" involves an air gap between two or more panes of glass, with a special metallic coating applied to the glass surface.
"Low-E" stands for Low Emissivity. Its main purpose is to reduce heat transfer between the interior and exterior. It offers high insulation and heat shielding properties, and some products also provide higher UV cut performance than general single-pane glass.
The type and composition of the glass used in windows determine how much UV radiation enters.
So, how can you check what type of window you have at home?
According to research by the Flat Glass Association, the use of Low-E insulated glass, which offers high thermal insulation, has been increasing since around 2005, when the Kyoto Protocol came into effect.
The pace of adoption varies by housing type. While it exceeded 80% for newly built detached houses in 2017, for collective housing such as new condominiums, it surpassed 40% in fiscal year 2019, reached 56.5% in fiscal year 2020, and 67.2% in fiscal year 2023.
From this trend, it is possible that condominiums built around 2006 do not use Low-E insulated glass.
However, not being Low-E is not the same as being single-pane glass. General insulated glass without a Low-E coating may also be used.
The situation also changes depending on the property specifications and the history of sash and window glass replacement. It is more reliable to check certification marks, product numbers on the glass or sash, and house specifications rather than judging solely by the age of the building.
If you are unsure, you can also inquire with the management company or construction company.
Even ordinary lace curtains are effective
Even adding a single layer of lace curtain to your window glass can further reduce UV radiation.
According to actual measurements by curtain retailers, even thin, ordinary lace curtains without a UV cut label were able to cut an additional 50-65% of UV radiation after it passed through the glass.
Some lace curtains with UV cut features boast even higher cut rates. However, performance varies by product, and a higher UV cut rate may make it harder to let in natural light. When purchasing, it's advisable to check the test values and quality indications of each product.
So, what level of effectiveness can be expected when combining float glass with ordinary lace curtains?
If the UV cut rate of float glass is 34% and that of a lace curtain without UV treatment is 52%, a simple calculation yields the following:
* UV rays passing through glass: 66%
* UV rays then passing through lace curtain: 66% × 48% = approximately 32%
* Total cut rate: approximately 68%
This is an estimated value obtained by multiplying figures from different experiments and studies. It is not a direct measurement of this specific combination.
Nevertheless, it serves as a guideline to understand that "combining with a lace curtain is more effective than just a single pane of glass."
How light hits the artwork is more important than the presence of a window
In a typical indoor setting, there's no need to be overly concerned about the presence or absence of windows.
UV rays entering through windows are reduced to some extent as they pass through the glass. Adding a lace curtain can further suppress them. The amount of UV rays generated by lighting is also significantly less compared to sunlight.
The most important everyday measure is not to avoid rooms with windows, but to choose a location where direct sunlight does not hit the artwork for long periods.
Close the lace curtains only during strong sunlight hours. Avoid placing the artwork directly against window glass. Do not continuously shine a strong spotlight from a close distance.
Such basic considerations make it easier to suppress the progression of fading.
Of course, it's impossible to completely eliminate light-induced fading. Still, there's no need to worry excessively about having a room with windows when enjoying art posters in a typical home.
Summary
* Other factors besides UV rays also contribute to fading, but UV protection is relatively easy to implement indoors.
* According to the comparative values referenced, the amount of UV radiation from lighting is approximately 0.4 for incandescent lamps, 0.1 for fluorescent lamps, and 0.002 for LED lighting, with direct sunlight at 100.
* For frame front materials, the ability to suppress fading of the artwork does not necessarily align with the material's own resistance to change.
* In the test referenced, PET sheets showed less fading of printed materials than glass, but slightly more than acrylic.
* PET sheets offer the advantages of being lightweight, shatter-resistant, and easy to handle in daily use.
* The amount of UV radiation entering indoors varies depending on the type and composition of window glass.
* Even ordinary lace curtains can be expected to have a certain effect as a UV protection measure.
* The degree and duration of exposure to direct sunlight or strong light are more important than the presence or absence of a window.
To enjoy your precious artwork for a long time, extensive measures are not necessary.
Avoid direct sunlight. Use lace curtains during strong sunlight hours. Do not continuously shine strong lights from nearby.
Why not try implementing feasible measures from both the frame and the display location?
The figure above was created by AI based on information from the Japan Meteorological Agency's website "Clouds and UV Rays."
【Source】
・Naito Picture Frame Specialty Store "Characteristics and Selection of Glass, Acrylic, UV Cut, etc. by Type"
・Acrylic Depot "Material Professional Explains! The Difference Between Acrylic and PET is 'Price' and 'Strength'"
・Yasui Shoten "[Conservation Framing] UV Cut Acrylic Effect Verification" (Tokyo Metropolitan Industrial Technology Research Center test)
・Tokyo Metropolitan Industrial Technology Research Center "Xenon Lamp Accelerated Weathering Tester" (Reference information for test conditions)
・Central Glass Products "Optical and Thermal Performance of Sheet Glass"
・PET Bottle Recycling Promotion Council "Safety of PET Bottles" "Characteristics of PET Resin"
・Curtain House Silk Midori Store "We Measured the UV Cut Rate of Lace Curtains"
・Flat Glass Association "Trends in the Penetration Rate of Insulated Glass / Low-E Insulated Glass"
・Ministry of Land, Infrastructure, Transport and Tourism "Study Group on Energy-Saving Measures for Housing and Buildings Towards a Decarbonized Society" Hearing Materials
・Ministry of the Environment "Akari Mirai Keikaku (Light Future Plan)"
・Journal of the Illuminating Engineering Institute of Japan "Development of LED Lighting (1) Overview of LED Lighting"
・Explanation document listing comparative values for UV radiation (sunlight 100, incandescent 0.4, fluorescent 0.1, LED 0.002)
*This column is compiled by referencing experimental and survey materials from multiple third parties. The performance of individual front materials, lighting fixtures, window glass, and curtains varies depending on the product. For precise specifications, please confirm with each manufacturer, management company, etc.
