Artwork fading due to LED lighting
Light-sensitive dyes, such as those in oil and watercolour paintings, are bleached by electromagnetic waves. The three parameters decisive for this circumstance are the wavelength spectrum, the irradiation time, and the distance from the object to the illuminant. The shorter the wavelengths of radiation, such as UV (ultraviolet=100–380 nm), violet (380–430 nm), and blue (430–480 nm), the stronger the bleaching effect. Long-wave light (>550 nm yellow to red) is harmless.
A lighting system's operator can influence this fading:
- Select an illuminant without UV and with a low blue content. These are usually warm white light colours with high colour rendering
- Limit the intensity of illumination.
- Limit the duration of irradiation.
- The distance to the object
Decisive lighting factors
For sensitive works of art, limited illuminance is common in any museum. At 12 hours a day, 7 days a week (84 hours), illuminance is limited to 50 lx. This corresponds to a weekly dose of 4200 lx/h. For example, art lovers can safely illuminate their works of art at 420 lx for 10 hours a week.
In addition to illuminance, the angle and distance of illumination have a major influence on the extent of fading in works of art. For example, narrow beam optics significantly increase illuminance compared to wide beam optics because they direct light to the object in a more targeted manner. Curators therefore like to use the museum spotlights’ DIM-POTI controllers to flexibly adjust the illuminance to the respective exhibits.
Observation of the light spectrum
The v λ curve weights the spectrum of a light source according to the human perception of brightness. Light green wavelengths appear brightest to humans. Blue and red wavelengths appear less bright to the human eye. Light sources with a high proportion of light green wavelengths generate a high illuminance on the exhibits. Harmful wavelengths for the exhibit, however, are short-wave <500 nm and are not covered by the unit lx (lux).
Measures to curb fading
Increase illumination distance
doubling the illumination distance is only the √ (root) of the original damage potential
The right light colour
Use warm white light colours <3000 K with a high colour rendering index Ra>90
Dim luminaires to the required intensity
Consider the angle
Use a wide-beam optic
Watch the time
Limit the lighting time