Short answer
Light fades many pigments and dyes, and the damage builds up with illuminance multiplied by hours, so conservators limit light: traditionally about 50 lux for highly sensitive works such as textiles, watercolours and photographs, and 150 lux for oil paintings. At those levels colours look less saturated than their makers saw them, which gallery lighting has to balance against preservation.
Visible light and, especially, ultraviolet break down many colourants. Conservation guidance treats the damage as approximately proportional to the total exposure — illuminance times hours — so 50 lux for a year does roughly what 100 lux does in six months. The Canadian Conservation Institute groups materials by sensitivity using the ISO blue wool scale and gives years to a 'just noticeable fade' under standard display assumptions. Its figures show why dimming is not optional: a highly sensitive textile or watercolour can show a first visible fade within a few years at 50 lux, and far faster in bright light.
Long-standing guidelines, still widely quoted, set about 50 lux for the most sensitive materials (textiles, works on paper, watercolours, photographs, feathers), about 150 lux for moderately sensitive ones such as oil and acrylic paintings and painted wood, and about 300 lux for stone and metal, where the limit is about visual comfort rather than fading. Ultraviolet is removed or kept very low, because it carries a large share of the damage while contributing little to seeing. More recent guidance frames the choice as a budget over years of display rather than a fixed ceiling, and some institutions rotate sensitive works into storage to rest.
At 50 lux the eye is still in daylight vision, but colours look less saturated and fine differences in dark passages are harder to see than at the several thousand lux of a painter's studio by a window. Lighting research reviewed alongside TM-30 notes that at very low light levels, such as a museum, a greater increase in chroma is needed for colours to look their best, and that preferred saturation falls as light rises. That is why some gallery lighting deliberately uses sources that slightly boost chroma, and why TM-30's specification annex expects custom criteria below 200 lux.
Modern galleries mostly use LED, whose phosphor-converted spectra contain very little ultraviolet — an advantage for conservation — but whose red rendering varies, which matters for flesh tones and earth pigments. Warm-white is common because it looks comfortable at low levels. Direction matters too: grazing light reveals brushwork and canvas texture, while glare from varnish or glazing hides colour. And visitors walking in from a bright atrium need time to adapt; well-planned galleries step light levels down gradually so that 50 lux does not feel dark.
| Sensitivity | Illuminance | Time to a just noticeable fade |
|---|---|---|
| High sensitivity | 50 lux | 2 years – 20 years |
| High sensitivity | 150 lux | 6 months – 7 years |
| High sensitivity | 1000 lux | 1 months – 1 years |
| Medium sensitivity | 50 lux | 20 years – 700 years |
| Medium sensitivity | 150 lux | 7 years – 233 years |
| Medium sensitivity | 1000 lux | 1 years – 35 years |
Why: It is lit to about 50 lux to protect it; colourfulness falls at low light.
Fix: Give your eyes time to adapt away from bright areas; the work's colours are as intended for its preservation.
Why: Daylight delivers many times museum light levels plus ultraviolet.
Fix: Hang sensitive works away from direct daylight, use UV-filtering glazing, and rotate them.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
ConventionStrong evidence
Traditional conservation guidelines set about 50 lux for highly sensitive materials, about 150 lux for moderately sensitive materials such as oil paintings, and about 300 lux for insensitive materials.
Source: Agent of deterioration: light, ultraviolet and infrared
FactStrong evidence
Conservation guidance treats light damage as proportional to illuminance multiplied by exposure time, and gives years to a just noticeable fade for sensitivity categories tied to ISO blue wool grades.
Caveat: Reciprocity is a working approximation; some materials depart from it.
Source: Agent of deterioration: light, ultraviolet and infrared
FactModerate evidence
At very low light levels such as those in museums, a greater increase in chroma relative to the reference is needed to achieve maximum preference.
Colourwise analysisModerate evidence
For a highly sensitive object displayed 3,000 hours a year, raising illuminance from 50 to 150 lux cuts the time to a just noticeable fade to a third.
Based on: Calculated by Colourwise from CCI's 50-lux figures by reciprocity; see the table.
Caveat: Assumes reciprocity and CCI's display-hours assumption.
Source: Agent of deterioration: light, ultraviolet and infrared
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.