Light and fading of printed artwork on walls: what slows it

Conservators think of light damage as an accumulated dose: the brightness reaching a surface (lux) multiplied by the hours it is lit [2]. For a wall, that means a bright spot for a short time and a dim spot for a long time can add up to the same total [3]. CCI's paintings guidance shows this with 200 lux for 200 hours, which does the same damage as 100 lux for 400 hours [3]. Halving the lit time has the same protective effect as halving the light level [3]. For worked sums, see how lux-hours add up on a wall.

Three factors set the damage: how much UV is in the light, how bright the light is, and how long the item is lit [1]. The damage also does not reverse. A faded photograph kept in the dark afterwards will not return to its original appearance [4], and CCI says no true recovery is possible from faded colours [2].

NEDCC and Museums and Galleries NSW describe UV as the most damaging part of the spectrum [1][4], but NEDCC stresses that visible light also does serious harm [4]. For the fading of light-sensitive colours specifically, CCI puts UV at less than half, and often only one tenth [2]. Visible light can fade or change colours in dyes and colorants, and can make paper fade, yellow or darken [4]. UV can weaken, bleach and yellow paper and other organic materials [4].

UV still matters, because it can also drive chemical damage in materials such as acidic paper and plastics [1]. Taking UV out of the light therefore does not take fading out.

Infrared plays a different role. NEDCC says it is damaging because it makes the surface of objects heat up [4]. CCI notes that organic materials exposed to sunlight can reach 40 degrees C [2].

UV is measured as a ratio, in microwatts per lumen. The long-standing guidance is to keep UV below 75 microwatts per lumen for sensitive materials [1][2][4]. CCI lists daylight through window glass at about 400 to 500 on that scale [2]. NEDCC says LEDs do not emit UV or IR radiation [4], while CCI lists white LED at 0 to 75 microwatts per lumen, described as very low [2], so check the lamp data sheet.

Conservators group materials by how easily light changes them. The Museums and Galleries NSW fact sheet puts paper prints, photographs, textiles and vegetable-dyed material in its most light-sensitive group, with a suggested maximum of 50 lux [1]. It puts oil, tempera and acrylic paintings and timber in a moderate group at 200 lux [1].

Be careful how you apply this. These documents describe museum collections. They do not test any specific digital ink, substrate or coating, so they cannot tell you how a given print will behave. Treat the table as a guide to the direction of risk. For a specific product, ask the maker of the ink or media for its lightfastness data.

CCI links sensitivity to the ISO Blue Wool scale. Ratings 1 to 3 are high sensitivity, 4 to 6 medium, and 7 and above low [2]. A lower number fades sooner.

Light levels differ enormously between a sunlit wall and a lamp-lit corner. CCI Notes give normal office light as 500 lux and average daylight as 30,000 lux [3]. NEDCC puts standard office lighting nearer 400 lux [4], so treat office figures as approximate. NEDCC likens 50 lux to the lighting in a home living room in the evening [4]. The rate of light damage is proportional to intensity, and CCI gives a 1,000-fold rise in intensity from good museum light levels to sunlight [2].

CCI estimates how long a just-noticeable fade takes, assuming 8 hours a day and 3,000 hours a year [2]. The estimates run across a wide range because materials differ. They are model figures for museum categories, so do not read them as predictions for a print on your wall.

The table below shows CCI's model estimate of the time to a just-noticeable fade at 50 lux, 500 lux and daylight levels [2][3].

The numbers below combine published figures with a simple multiplication. The scenario itself is invented, and it is not a forecast for any ArtzFolio product.

• Dose per year. Take a wall lit at 500 lux, the office level in [3], for 3,000 hours a year, the exposure CCI assumes [2]. Dose is 500 x 3,000 = 1,500,000 lux-hours, or 1.5 million lux-hours (arithmetic from the figures in [2] and [3]).
• Compare with a published threshold. CCI publishes a table of just-noticeable-fade doses by Blue Wool rating [2]. On that arithmetic, 1.5 million lux-hours is the dose CCI lists for a just-noticeable change in Blue Wool 3 with UV present [2]. This only shows how the figures relate. It is not a forecast for any print. The same CCI table, UV-present row, gives 8 million for Blue Wool 5 and 50 million for Blue Wool 7 [2]. With UV removed it lists higher doses, such as 3 million for Blue Wool 3 [2].
• Same dose, different route. Applying the equal-damage rule [3], halving the lit hours from 3,000 to 1,500 a year at 500 lux gives 750,000 lux-hours, the same dose as 250 lux for 3,000 hours (arithmetic: 500 x 1,500 = 750,000 and 250 x 3,000 = 750,000).

The lesson is the relationship, not a date. Whether any print reaches a given dose depends on its materials, which none of these guides assess.

UV-filtering glazing removes part of the problem. CCI Notes say UV-absorbing films reduce UV damage but "will not mitigate the fading caused by visible light" [3]. UV-absorbing acrylic filters out varying percentages of UV depending on the acrylic [3]. Museums and Galleries NSW also suggests UV-absorbing acrylic when framing prints [1]. For what filtering glazing blocks, see what UV-filtering glazing blocks and what it does not. For a comparison of glazing types, see acrylic versus glass glazing for picture frames.

Ordinary window glass is not a full answer either. CCI says it blocks shortwave UV but not enough for museums [2].

Filters age. NEDCC says high-quality UV-filtering films can remain effective for approximately 15 to 20 years depending on location, and that the only way to know if a film still filters is to measure with a UV meter [4]. Treat any quoted life as an estimate.

Tinted films also lower visible light [3]. That helps slow fading but changes how the room looks.

Because dose is lux times hours, placement and habits act on both factors.

• Avoid direct sun. CCI advises that where windows have no UV filters, objects should be placed where no direct window light reaches them [2]. NEDCC advises displaying sensitive items away from direct light, including sunlight and spotlights [4].
• Add distance. Lux falls as the light source moves further from the item [1].
• Control daylight. Heavy curtains, diffusing blinds, exterior shutters or UV-filtering window material can all reduce daylight [1]. Daylight also varies by time of day, season and weather, which makes levels hard to control [1].
• Choose low-UV lamps. Check UV output on the lamp data sheet. White LEDs are listed at 0 to 75 microwatts per lumen [2].
• Cut lit hours. Switch lights off when no one is in the room [2]. Timers and movement switches also limit exposure time [1].
• Rotate display. Limit how long sensitive items stay on display and rest them afterwards. One museum guide gives a watercolour on display for three months per year as an example, and adds that an item shown for a year should not be shown for the next three years [1].

For rooms with many frames, such as hotels, plan wall positions against windows and lamps early. Our hotel room wall art plan covers layout.

No fade time can be promised from general guidance. The guides above give model estimates for museum categories under stated assumptions [2]. A real wall differs in light level, hours, UV content, heat and the print's own materials. Ink type matters as well, see dye ink versus pigment ink lightfastness, and for printed fabric see colour-fastness tests for printed fabric. For how colour is handled in file preparation, see our canvas print resolution and colour guide.

Sensible expectations for a buyer: put prints away from direct sun, use UV-filtering glazing where it suits the product, reduce lit hours, and ask for lightfastness data from the ink or media supplier. Treat any seller who quotes a fixed number of years without stating the light conditions with caution.

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1. Light damage and light control, Museums and Galleries NSW. mgnsw.org.au
2. Agent of Deterioration: Light, Ultraviolet and Infrared, Canadian Conservation Institute. canada.ca
3. Environmental Guidelines for Paintings, CCI Notes 10/4, Canadian Conservation Institute. canada.ca
4. Preservation Leaflet 02-04: Protection from Light Damage, Northeast Document Conservation Center (NEDCC). nedcc.org