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PostHow Does Flash Photography Damage Works of Art? (Consoly Leon Arias, Spain / Canary, 08/13/22 3:39 am)
In response to my post about the prohibition of photography at the Sistine Chapel, John E asked whether the claim that flash photography damages a work of art is true or myth.
On countless occasions we have seen prohibitions against photographs and/or videos in any of the thousands of museum spaces scattered around the world, and we can assume that taking a flash photograph of a work of art is a disrespectful gesture, but to what extent is this brief exposure to an intense flash of light harmful to the work itself?
There is no doubt that to enjoy a work of art in all its splendor it must be properly illuminated. But light is, at the same time, a constant enemy that relentlessly attacks the different components of a work of art, especially paintings, causing them to alter over time. In fact, it is one of the ten most common agents of deterioration, which also include heat and humidity. From a physical point of view, light is a form of energy, with dual behavior, and is made up of photons that exhibit both wave and particle properties. For their part, the molecules that make up matter also have different energy levels. Thus, when the energy difference between two levels coincides with that of a photon incident on the physical matter, the molecules will absorb it in order to pass from one level to another. When this happens, the molecule is said to be excited because it is at a higher energy level. Once in this state, most of the time, the molecules relax and release energy (in the form of light or heat) but it can also happen that a bond between atoms breaks. It is in this case when the molecule degrades, giving rise to another compound with different properties. Surely everyone has seen this damaging effect of light on an object exposed for a long time in a store window. If we talk about works of art, the degradation of pigments can cause an irreversible alteration of the color, and therefore greatly damage the artistic work.
Sometimes it is possible that a painting has suffered such degradation due to the impact of overexposure to sunlight or light from a photographic device, that when we look at it we do not see what the painter really wanted to reflect when he or she painted it. Some examples that show this degradation are: Van Gogh's The Room at Arles, or Edward Hopper's Cape Cod Evening.
Of course light can damage works of art, but how much light is necessary for this to happen? The duration of a flash shot is only a thousandth of a second, so can such a brief but intense exposure threaten a work of art? Before answering this question we need to understand two concepts: illuminance and the reciprocity principle.
Illuminance is the amount of light incident on a surface and the unit in which it is measured is called lux. The reciprocity principle is fulfilled when the degradation that a substance undergoes is proportional to the total energy it receives. If this principle is fulfilled, knowing the illuminance caused by two different sources (for example a flash and the spotlights of a gallery) on a work of art, we can compare their effects.
The amount of energy emitted by a flash depends on several factors, but we can say that one flash of a flash is equivalent to an exposure of 600 lux for one second (0.17 lux in one hour). So, knowing that in museums such as the National Gallery in London, the lighting system in many of the rooms is 200 lux, we can calculate that being under that lighting for an hour is the same as experiencing 1,200 flashes. If this museum were open every day of the year for eight hours a day, the energy received by the works would be equivalent to three and a half million flashes. Clearly, the damage caused by each flash is negligible, but let's put it in perspective. If half of the visitors who come to the British gallery every year were to take a photo of the same work, it would suffer the same damage from the museum's lighting as from the flashes. Some will say that by doing this we are doubling the "aging" of the works and others will say that if the museum lighting is prepared not to damage the works, neither will three million flashes.
In any case, empirical tests have been carried out to study whether the effect of light on pigments is linear (i.e. whether the principle of reciprocity is fulfilled). One of the most important studies was carried out in 1995, by David Saunders, precisely for the National Gallery. The results showed that the reciprocity principle was fulfilled for the vast majority of pigments. That is, after receiving an equal amount of energy, the pigments underwent comparable degradation regardless of whether this light came from the gallery lighting or from the flash of the UV-filtered camera. However, the samples exposed to the unfiltered flash did suffer greater degradation, demonstrating how damaging ultraviolet radiation is to works of art. Finally, nowadays cameras filter that region of the electromagnetic spectrum produced by the xenon lamps of flashes. Similarly, it should be noted that not only pigments can degrade, since light also deteriorates support materials such as paper, silk, wool and some varnishes. To protect this kind of more sensitive works, there are precisely those museum rooms with dimmed light and regulated humidity and temperature conditions.
JE comments: Very clear explanation, Consoly; thanks! My takeaway from the above is that flash photography is no more damaging than the ambient lighting, although every extra photon takes its toll. The biggest reason to prohibit the flash in art museums is likely practical: it's annoying to other patrons.