The Canadian Conservation Institute puts the safest relative humidity for paintings on canvas or wood at a stable level between 40 and 60%, with a temperature set point anywhere in the range of 16 to 25 degrees Celsius. For light, it notes that most colours read reasonably well at 50 lux, and that detail in darker colours may require 150 lux. Where ultraviolet radiation cannot be blocked entirely, levels should not exceed 75 microwatts per lumen.
These are museum figures, and they can look intimidating written down. They are not. A normal heated, lived-in Canadian home sits inside the humidity and temperature ranges most of the year without anyone doing anything. The figures matter because they tell you which situations actually fall outside them, and those situations are specific and avoidable.
Key takeaways
- Stability matters more than the exact number. A steady 45% is better for a painting than one that swings between 35% and 60% every week.
- Light damage is cumulative and irreversible. There is no restoration for a faded pigment.
- Ultraviolet is the most damaging part of the spectrum, and it comes from daylight and fluorescent lamps.
- Placement does most of the work. Equipment is a distant second.
Humidity, and why movement is the problem
A painting on canvas is a composite of materials that respond differently to moisture. The canvas absorbs water from the air and swells, then releases it and contracts. The ground and paint layers above are much less flexible and cannot follow that movement indefinitely. Each cycle puts stress into the paint film, and over enough cycles that stress appears as the fine network of cracks called craquelure, and eventually as paint lifting away from the support.
This is why the guidance emphasises a stable level rather than a precise target. A painting kept steadily at 45% is in better condition after twenty years than one that averages 50% while swinging between 35% and 65% with the seasons and the weather.
Panel paintings on wood are more sensitive again, because wood moves more decisively than canvas and can split or warp.
Where homes fall outside the range. Bathrooms and the walls beside them, because every shower spikes the humidity. Unheated basements, which run damp and cold. Attics and garages, which swing with the outside weather. Rooms with a wood stove or open fire in winter, which can drop very dry. And the wall directly above a working fireplace, which combines heat, soot and repeated cycling.
What actually helps. Choosing an interior wall in a room you heat and live in solves this for most people at no cost. Where a home genuinely runs dry in winter, a humidifier set to hold a steady level does more good than one used occasionally. An inexpensive hygrometer hung near the painting tells you whether you have a problem at all, which is worth knowing before buying equipment to solve one you may not have.
Light, and why the damage never comes back
Light fades pigment through a photochemical reaction. Once a molecule of colourant has broken down it is gone, and no conservation treatment restores it. Retouching can disguise a fading, but the original is not recoverable. This is the reason museums keep galleries dimmer than most visitors expect.
The damage is cumulative, and it trades off against time. The CCI illustrates this directly: exposure to 200 lux for 200 hours produces the same damage as 100 lux for 400 hours, or 50 lux for 800 hours. A painting on a bright wall is not safe because each individual day seems harmless; the days add together.
Pigments differ enormously in sensitivity. Some earth colours are extremely stable, while certain organic reds, yellows and dyes fade quickly. Because a buyer cannot tell which are present by looking, the safe assumption is that the painting contains something vulnerable.
What actually helps. Keep paintings off any wall that receives direct sunlight at any point in the day, in any season, which is the single most effective step available. Close blinds in rooms that are unoccupied during the brightest hours. Use lamps that put light on the room rather than aimed at the painting, and if a picture light is used, keep it modest and switch it off when the room is empty. Rotating works, so a piece spends part of the year away from the light, is exactly the intermittent display the CCI describes, and it works.
Ultraviolet, specifically
Ultraviolet radiation carries more energy than visible light and does proportionally more damage, while contributing nothing to how the painting looks. Removing it costs nothing in appearance, which makes it the easiest win available.
Daylight is the main source, including daylight through an ordinary window. Fluorescent lamps are the other: the CCI notes they emit in the low-to-medium range of 75 to 150 microwatts per lumen and will require UV filters. Where UV cannot be blocked completely, the published limit is 75 microwatts per lumen.
What actually helps. UV-filtering glazing on framed works on paper, which is a standard framing option and worth specifying. UV-filtering film on windows in a room where art hangs. LED lighting, which emits very little ultraviolet. Oil paintings on canvas are usually displayed unglazed, so for those, placement away from windows is the control.
The numbers in one table
| Factor |
Published guidance |
Practical control |
| Relative humidity |
Stable, between 40 and 60% |
Interior wall, heated room. Hygrometer to confirm. Humidifier only if genuinely dry. |
| Temperature |
Set point in the range 16 to 25 degrees Celsius |
Normal room temperature. Avoid walls above radiators and fireplaces. |
| Visible light |
50 lux for most colours, 150 lux for detail in dark colours |
No direct sun. Modest ambient lighting. Rotate works if a wall is bright. |
| Ultraviolet |
Not to exceed 75 microwatts per lumen where it cannot be blocked |
UV-filtering glazing on framed paper. LED lamps. Window film. |
Source: Canadian Conservation Institute, CCI Note 10/4, Environmental Guidelines for Paintings, published 1990 and revised 2016. Figures as published and checked on 5 September 2026.
A realistic standard for a home
Nobody is suggesting you run a house as a museum. The useful translation of all of the above is short. Pick an interior wall in a room you heat and use, out of direct sunlight, away from the bathroom, the fireplace and the radiator. Hang a cheap hygrometer nearby and glance at it occasionally. Specify UV-filtering glazing when framing anything on paper. Look at the painting once a year in good light.
That is the whole programme, and it costs almost nothing. Our page on caring for an original painting covers the handling and yearly check, and custom framing covers glazing choices in detail.
Frequently asked questions
What humidity level is safe for paintings?
The Canadian Conservation Institute states that the safest relative humidity for paintings on canvas or wood is a stable level between 40 and 60%. Stability is the more important half of that guidance, because repeated swings make the canvas expand and contract while the paint layer above cannot follow, which produces cracking over time. A steady 45% is better than an average of 50% that moves constantly.
How many lux is safe for displaying a painting?
The Canadian Conservation Institute notes that most colours are perceived reasonably well at 50 lux, and that detail in darker colours may require 150 lux. Lower is always safer, because light damage accumulates: the CCI illustrates that 200 lux for 200 hours does the same damage as 50 lux for 800 hours. There is no threshold below which light causes no damage at all to sensitive pigments.
Why can faded pigment not be restored?
Fading is a photochemical reaction that breaks down the colourant molecules themselves, so the original colour no longer physically exists in the paint layer. A conservator can retouch to disguise a loss, but that is new material added on top rather than recovery of what was there. This irreversibility is why prevention through placement matters far more for light than for almost any other risk.
Is ultraviolet light worse than visible light for paintings?
Ultraviolet radiation carries more energy than visible light and causes proportionally more damage while contributing nothing to how a painting looks, which makes filtering it the easiest protective step available. The Canadian Conservation Institute advises that where UV cannot be blocked completely, levels should not exceed 75 microwatts per lumen, and notes that fluorescent lamps emit in the 75 to 150 range and need filters.
Do I need a humidifier for my paintings?
Most heated, lived-in Canadian homes stay within the 40 to 60% range for much of the year without any intervention, so a humidifier is often unnecessary. Hang an inexpensive hygrometer near the painting first and observe it across a season before buying equipment. If the reading does run persistently low in winter, a humidifier held at a steady level helps more than one used occasionally.
Does UV-filtering glass protect an oil painting?
UV-filtering glazing protects works that are framed behind glass, which usually means works on paper, watercolours and drawings. Oil and acrylic paintings on canvas are normally displayed unglazed as a deliberate choice about how the surface reads, so for those the control is placement away from windows and direct sun rather than glazing. Where a canvas is glazed, UV-filtering glass is worth specifying.
Can I hang a painting in a room with large windows?
A room with large windows is usable provided the painting is not on a wall that receives direct sunlight at any point in the day or season. Reflected daylight is far less damaging than a direct beam. UV-filtering film on the windows reduces the risk further, and closing blinds while the room is empty during the brightest hours costs nothing and meaningfully cuts cumulative exposure.
What temperature is too cold for a painting?
The Canadian Conservation Institute gives a recommended set point anywhere in the range of 16 to 25 degrees Celsius, so an unheated space that drops well below 16 falls outside it. Cold itself is less damaging than the humidity swings that accompany unheated spaces, which is why basements, attics and garages are poor locations regardless of the temperature reading alone.
Does rotating paintings actually help?
Rotating paintings helps because light damage depends on total cumulative exposure, so a work that spends part of the year away from a bright wall receives proportionally less. The Canadian Conservation Institute describes intermittent display, meaning shortening the periods of exposure, as a way to slow fading. It is the practical option for anyone whose only good wall happens to be a bright one.
How do I measure the light level on my wall?
A lux meter measures light levels directly, and inexpensive handheld units and phone applications both give readings adequate for deciding whether a wall is bright or dim. Take a reading at the painting's surface at the brightest time of day rather than in the evening. For most homes the answer is obvious without a meter: if direct sunlight reaches the wall, the level is too high.
Sources and references
Each link was opened and confirmed to resolve on 5 September 2026.
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Environmental Guidelines for Paintings, CCI Notes 10/4. Canadian Conservation Institute, Government of Canada. Published 1990, revised 2016. Accessed 5 September 2026. Source for every figure on this page: the 40 to 60% relative humidity range, the 16 to 25 degrees Celsius set point, the 50 and 150 lux figures, the 200 lux for 200 hours equivalence, and the 75 microwatts per lumen ultraviolet limit including the 75 to 150 range for fluorescent lamps.
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Storage and Display Guidelines for Paintings, CCI Notes 10/3. Canadian Conservation Institute, Government of Canada. Published 1986, revised 2016. Accessed 5 September 2026.
