Flash causing yellowing?

I think you will find it difficult to get hard evidence on this as it will be virtually impossible to patial out any yellowing effect of a flash from that caused by ambient light. The only situation I can imagine that would settle it is if someone kept their doll in a dark box and only got it out to take flash photos. The isolated effect of the flash could therefore be seen. But, yes, highly unlikely to happen.

If the info you present is reliable data from gallery/museum studies, I would go with that. So, flash is harmless, relatively speaking.

 

Any light carries energy. Whether it's infrared heat, visible or UV, all of them will contribute to changes we call aging. The best anyone can really do is slow the process.

Natural light can range from "north facing window" to "left in the sun", which will have very different speeds as to how yellowed your doll will get. So I believe it is reasonable to say that how much power your flashes use matters as well. Low ISO makes your flash dump more power for the same exposure. Close positioning of the flash head to the doll has heat risk - flashes get really hot when firing, especially hotshoe and larger sizes.

But I think any effects would be pretty minor - indistinguishable from normal aging - unless you do something extreme like shoot the doll all day every day for months.

 

All light — or rather, all electromagnetic radiation — carries energy, yes, but shorter (blue to ultra violet, and beyond) wavelengths carry considerably more of it than longer (red to infra red, and beyond).

Yellowing is the visible result of the polyurethane aging, i.e. the polymer chains breaking down.
UV light actively contributes to this process, while visible and IR wavelengths are, to all practical intents and purposes, harmless.

It is sort of not unlike the fact that indefinite exposure to visible light and IR radiation (=heat) is harmless for humans, but prolonged exposure to UV light (as in sunlight) can cause skin cancer by damaging the DNA (another organic molecule chain) in skin cells.


(Here are a couple of earlier threads that have discussed the implications of light/heat on doll welfare:

• BJDs and Halogen/Tungsten lighting
• Using Studio Lights??)
  

Flashes do emit some UV radiation, yes, but the amount is so minute that it is not going to make any difference whatsoever to your doll, regardless of what strobes you use, or how avid a photographer you are. Anything else would be sort of like photo models risking melanoma from being strobed all day...

Continuous lights may be another matter, depending on what kind of a light source the lamps use. Tungsten lights are completely harmless, but fluorescents or LED's may be more of an issue, as these do emit a certain UV component.
How large an issue is however relative: are you wary about having your doll in a room with unshuttered north-facing windows? Or do you take care never to have your doll in a room lit by fluorescent tubes (including those in CFL's)?
If these conditions do not bother you, then continuous studio lights probably won't be a problem, either.
As a rule of thumb I'd say that if the UV radiation isn't anywhere strong enough to tan your skin after prolonged exposure, short-term exposure won't harm your doll noticeably.

Thermal radiation in the IR wavelengths as such will not cause yellowing, but if heat is allowed to build up excessively in the doll, it may become an issue. This point is addressed in the first of the threads linked to above.

 

I just want to clarify something about artificial lighting VS sunlight in terms of yellowing. To be exact there was once a scientific paper that did a measurement for CFL bulbs but you can pretty much relate it to all artificial lighting. Why you may ask, well below is some numbers to ponder about.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2868278/

this article talks about output of UV in CFL. Well to cut it short, the sun around sunset outputs 10k units of uv. The most deadly cf bulb of UV emission at 13w does a mear 89 if the item is 20cm away. So if you think about it, exposure to the sun for 5 min, you can expose your doll to the most deadly CFL light for like 500min at 20cm. Now no one puts their dolls 20cm from a CFL, so base on how light works, a drop in power for every 60% increment in distance. Just putting your doll at 32 cm drops it to half that value and 50cm another half of that. To say you can yellow under CFL is true, but 5 min in the sun is probably more deadly then your entire year under a CFL bulb for your dolls.

So lets return to the issue with flash. Now we know flashes can beat the sunlight in small pulses. Assuming the flash produce a full light spectrum like the sun, you can say its a sun for that small period. However take into consideration this, flash last for a meer 1/1000-1/200s. And in that time frame it produces more light(and more uv) then the sun in about 1/100s (people who do photography will know what I mean, light is accumulative). If the flash was unshielded, it will produce that amount of UV in its light at that small release moment.

Lets take into consideration this article
http://people.pwf.cam.ac.uk/mhe1000/musphoto/flashphoto.htm

it talks about how much UV will damage artwork and what is the allowed flash amount to take artwork. Theres no exact numbers but flash below a certain power deals very little damage to artworks. However one of the most important point in the article talks about the material that covers flash. To be precise, most flash is covered by glass. And glass blocks most spectrums of harmful UV. Unless you are using special lights that uses quartz as the cover material (which is used for specific purpose) that allows all light, a good amount of UV is already filtered off.

Take into consideration of both point, I can conclude that yes flash can yellow your doll, if you fire it non stop at a high rate over a really long period of time. Other than that I doubt it will do any more harm then 5 min of evening sunlight lol.

This is base of my understanding and if I am wrong someone do explain it to me and I will correct my answer.

 

Brilliant and informative, zerartul -- thanks! That ought to put a cap on the issue.

 

I never thought of this. though it does seem kind of plausable. my doll has white skin so I don't tend to use a flash when taking pictures of him because he just looks washed out when I do. but I can't imagine the flash on a camera really doing too much damage.

 

all good to know thanks

 

This is great information, thanks to everyone!