Good lighting is essential for a work of art

Lighting can be natural or artificial.

A natural light source is ideal, but varies according to the time of day, weather conditions, natural shadows and the work's position in the room.

Sunlight heats up and emits ultraviolet light, which is destructive to a painting or photograph.

If you want constant, controlled lighting, artificial light is the way to go.

Halogen and tungsten bulbs were of excellent quality, but they heated up and emitted UV rays.

The most suitable choice is Led, but not just any Led.

There are several types with different characteristics.

They have a lighting temperature, i.e. a white light with a yellow, neutral or blue cast.

 White light with a yellow cast is called "warm color" and has a color temperature of around 3,000°K.

• White light with a blue cast is called "cold color" and has a color temperature of around 6,000°K.
• Neutral white light has a color temperature of around 4,000°K.

At Kartlight, we offer 3,000°K and 4,000°K, which are ideal for interiors.

3,000°K for warm ambience and 4,000°K for neutral rendering

Commercial LEDs do not have the same colorimetric quality.

• The LEDs used in low-end lighting have a CRI of 80.
• High-quality LEDs have a CRI of over 95.

K'artlight LEDs offer a Color Rendering Index according to the TM30-18 standard of over 96 (out of 100, which is sunlight). CRI stands for Color Index Rendering.

Color rendering index

Quantitative evaluation of the degree of agreement between the psychophysical color of an object illuminated by the test illuminant and that of the same object illuminated by the reference illuminant - the chromatic adaptation state having been correctly taken into account.

TM 30-18 was established in October 2018, developed by the Illuminating Engineering Society (IES) of North America.

•  Meticulous selection of 99 color samples - chosen from a database of over 105,000 references

- Continuity of reference sources, with a change introduced between 4,500 °K and 5,500 °K by mixing the daylight and blackbody referents to avoid the break at 5,000 °K.

The Rf reference index, calculated with reference sources and color samples, is highly precise and relevant.

TM 30-18 offers :

•  Rg saturation index (Gamut index)
•  A vector graphic representation of hue/saturation distortion
•  Four detailed values (Rf,skin: skin fidelity, Rf#: fidelity per hue, Rc#: chromatic variation per hue and Rf,CES#: fidelity per sample).

The TM 30-18 color rendering evaluation method is therefore both more precise and more comprehensive than the IRC established in 1995.

Comparison of the colorimetric spectrum of sunlight and K'artLight lighting

The back curve is that of the sun and the front curve is that of the Led K'artlight.

Light intensity 

We recommend illuminating paintings at 300 Lux (this is the standard used in museums).

The K'artlight light has a luminous intensity of 100 lumens.

Equipped with asymmetrical, ultra-transparent PMMA optics, it illuminates the work at 50 cm at 300 Lux.

Battery life

Continuous autonomy is 15 h with the 5,000 mAh battery with single-source lamps (Silhouette and Venus), corresponding to 750 automatic switch-ons. 20 switch-ons per day provide 37 days of autonomy, and 10 switch-ons per day 74 days.

Exposure to 100 passages per day provides a week's lighting without recharging the battery at maximum intensity.

As the light intensity can be adjusted, you can reduce power consumption and thus increase autonomy.

For example, reducing light intensity by 50% doubles battery life.

In the case of a 5,000 mAh battery, this means 24 hours, and therefore 1,500 switch-ons or 150 days with 10 daily switch-ons.   

Definitions of technical lighting terms

CRI Color Rendering Index

Reference: https: //fr.wikipedia.org/wiki/Indice_de_rendu_de_couleur

CRI Color Rendering Index

Wikipedia: https: //en.wikipedia.org/wiki/Color_rendering_index

Light intensity

The smallest possible part of the luminous flux in a single direction.
A source doesn't necessarily emit light equally in all directions. It is therefore useful to know the flux radiated in each direction.
Symbol: Iv
Unit: Candela (cd) lumen per steradian.

Illumination

The illuminance of a surface is equal to the luminous flux (in Lumen) falling on each m² of that surface.
Symbol: E (formula based on luminous flux) E = Luminous flux / Surface
Unit: Lux (lx)

Lux is equivalent to the illuminance of a 1 m² surface receiving a uniformly distributed luminous flux of 1 Lumen.

Luminance

Luminance is the number of candela per m² of apparent surface.
It characterizes the luminous appearance of an illuminated surface or source in a specific direction. A primary (spotlight) or secondary (reflective surface) light source emits light rays towards the eye. The sum of these light rays forms the image of the light source on the retina. The luminance of a surface depends on the luminous flux received, the degree of reflection of the surface and the direction of observation in relation to the light source illuminating the surface.
Symbol: L

Unit: candela per m² (Cd/m²)

Metamerism: a phenomenon revealed in poor light

Excerpt from : Metamerism - The problem of retouching in blue tones

Gaëlle Leclercq

https://doi.org/10.4000/ceroart.1818

In the field of conservation-restoration, metamerism is a very annoying optical phenomenon. Restorers sometimes notice a change in hue in their retouching work when the work is returned to the museum or its owner. In this case, the phenomenon of metamerism is revealed by a change in lighting. As the lighting conditions in an exhibition environment are not the same as those in a restoration workshop, they can reveal to the human observer that the retouching does not have the same spectral composition as the surrounding paint layer. The perception of this phenomenon can vary according to the visual sensitivity of the human subject, and it can also be revealed during photography.

Finally, it should be noted that while there is currently no solution that would eliminate this problem in restoration work, certain precautionary measures can be taken to avoid it as much as possible:

• Choose a light source with as uniform a spectral distribution as possible.

Another advantage of K'artlight lighting: retinal protection

A normal LED generates a blue peak that stimulates the retina, but can damage it if the intensity is too high and long-lasting.

Information taken from: "Guide de la lumière", Bruno Charmay https://leclairage.fr

Age-related Macular Degeneration (AMD): https://leclairage.fr/lumiere-bleue/

Extract

Another proven effect of blue light - but this time in shorter wavelengths (peaking at 430 nm, i.e. in violet blue) - is to promote the degeneration of retinal cells: electromagnetic waves with wavelengths between 415 nm and 455 nm can therefore accelerate this disease, and certain optical devices (such as eyeglasses) filter these waves.

Photo-spectrometer measurements on the K'ArtLight lamp 

CRI defined by CIE 13.3 : 1995 and FD X 08-018 (before 2018) : Ra = 99 and R9 = 98

CRI according to TM30-18 (since 2018): Rf = 98 and Rg = 101