Light and laser effects on surfaces. How and why do they cause a material to decay?

Question

Anyone that's been in a museum knows that's it's forbidden to photograph mainly old or very deteriorated crafts using a flash, but what is the reason for this? I don't see how a burst of relatively low intensity, non-ionizing radiation can have a long-term harmful effect on every kind of material. Or is it that some flashes radiate ionizing frequencies/intensities? Last equinox, at the (if I'm not mistaken) Kukulcan pyramid in Mexico, there was a festival in which they projected a series of lights at it as can be seen in this Facebook video and this sparked a discussion between me and my friends because one of them thought they were lasers and they were harmful to the structure according to one of his recent classes.

I think it's appropriate to break down the question into the following:

• What is the actual effect flash lights from cameras have on materials?

• If there is such, how is it generated and how does it differ from other light sources?

• Could an adequate-power-laser-show really harm a structure like an old pyramid? Are there any differences between the kind of erosion or decay caused by lasers and flashes?

EDIT

Please try to interpret the question in the broader sense, with the laser and pyramid example, not just the use of flash in a museum.

Answer 1

What is the actual effect flash lights from cameras have on materials?

That depends on the specific flash and the specific materials. From a physics standpoint, we can discuss the mechanism that can take place.

As light reaches a material, it has the potential to be absorbed. If the light has more than a specific amount of energy, it can transfer that energy to break a molecular bond. Breaking bonds degrades the original material. This photosensitive destruction can change the appearance (bleaching/fading) and compromise the strength of materials. Photodegradation.

While UV has more energy and is potentially more harmful, some materials are damaged even by exposure to visible light.

If there is such, how is it generated and how does it differ from other light sources?

Most camera flashes do not differ greatly from other lights. They may be more intense, but will not be on for long. Depending on the construction, they could generate higher frequency light than regular lighting, but almost any consumer flash is going to have UV filters to prevent significant amounts of UV from being released.

It's certainly possible to make flash bulbs that don't filter UV for special purposes as well, but that's not a standard flash. Those items would be more damaging, though.

Could an adequate-power-laser-show really harm a structure like an old pyramid? Are there any differences between the kind of erosion or decay caused by lasers and flashes?

In general, I would be completely unconcerned with anything outside. Unless it's some very special device, the flash or laser won't do anything that extended sun exposure hasn't done.

Limiting the total exposure of a painting is very different than worrying about the color of light you're shining on a stone outside.

Also:

Does flash photography really damage art? The persistence of a myth.

Does camera flash destroy art? Skeptics.SE