LEDS and Lighting Art

18-01-2013

2013 opened with a shock for the LED industry with a scientific report accusing LEDs of altering the colour of pigments in Van Gogh's masterpiece Sunflowers. There has been general consternation and cries of it cannot be true, but we have to accept that something was tested and something was damaged. Where does that leave us?

As far as we are aware, the tests on the pigments were carried out using an LED source that should never be used in lighting artworks. And whilst that doesn't help the standing of the report , it does confirm the advice of the best LED companies that only top quality product, properly suited for the application, should be used in these kind of critical situations.

Curators need to be aware that there are a number of factors that must be taken into account when considering any kind of artificial lighting installation and the use of LED in particular.

Light damage is caused to all pigments, dyes, inks, and sensitive materials unless they are kept in a zero-light condition. That much has been known for many years and explains why many precious documents and fabrics are only available for viewing by special appointment. The rest of the time they are kept safely away from any source of illumination.
It is an ongoing conflict that galleries and museums are obliged to make artworks available for public viewing in the knowledge that the objects themselves are slowly being degraded in the process.

The degree of damage is mitigated by carefully controlling the amount and quality of the light and the length of exposure time:

* the amount of light to which the artwork is exposed, considered in Lux hours / year.
Put crudely, the same amount of degradation is caused whether 20 Lux is delivered for 100 hours, or 100 Lux for 20 hours.

* the colour of the light, as defined by the Spectral Power Distribution of the light source. This is where the real damage is done. Materials are affected by particular parts of the visible light spectrum, with BLUE generally being the greatest culprit.

* the sensitivity of the materials being illuminated
at one end of the scale there is rock at the other end of the scale there is paper.

Into this scenario we must add the technical performance of a light source. There are four sources that are applicable to gallery and museum lighting:
* tungsten filament lamps no longer considered appropriate because of their poor energy performance and heat production
* tungsten halogen lamps considered by many to be the epitome of display lighting, but actually not good in terms of its ultra-violet light content and, of course, its poor energy performance.
* fluorescent lamps when used imaginatively, this energy-efficient source can create fine display conditions, but their physical size works against them and, again, the light has an unacceptable UV content that needs to be filtered away.
* and LED which is the reason for this entire piece.

Lighting and the LED:
as you can see, there is no perfect light source whenever conservation is a consideration. Even natural daylight wreaks havoc, as we've all experienced with our faded curtain fabrics at home. And its possible that too much has been made of the LED and its role as the saviour of lighting. In truth, It has brought its own problems.

There is a common factor with the light sources that came before the LED: they were each constant in their technical characteristics. Tungsten filament lamps all worked the same way; tungsten halogen lamps enjoyed their own little quirks; even the fluorescent lamp, which was the first blended light source, offered a consistency within its ranges. The designer and the curator knew where they stood. This is not the case with the LED.

As said above, its believed that the damage done to the Van Gogh pigments was due to an inappropriate LED light source one that delivered far too much BLUE light in its Spectral Power Distribution and at far too high an illumination level. No respectable lighting manufacturer or designer would consider such a source for this kind of use.

Let's be clear:
* LEDs for the illumination of artworks and where light sensitivity is an issue must have a controlled short wavelength output (the BLUE end of the spectrum).
* That means we need to be thinking in terms of fine-control of the white light production, with colour temperatures not exceeding 4000K, and preferably being at the warmer end of the spectrum (2700K - 3000K).
* The colour rendering index should be above Ra.90.
* The LED module should come with a guarantee of its future performance, usually stating its Colour Constancy tolerances.

And the curator should be looking for a reliable company with a good performance record in this sector. Its usually the case that good LED light fixtures are the result of an alliance between the manufacturer of the LED module and the manufacturer of the luminaire. This cooperation ensures that the best available lighting solutions to market.