I did too until I read CIE 157:2004 which made me realize that the studies that I’ve read, deal with flashes in isolation. That is to say, without consideration of the already existing exhibition lighting.



They start with the assumption of ISO 100 film shot at f/8. The flash delivers and exposure of about 600 lux seconds in 1/1000 of a second. Apparently the possibility of biphotonic reactions has been studied and dismissed (more than one photon hitting a molecule in such rapid succession that there is no time for energy loss between them and their affect is additive.)



So the exposure is roughly 0.17 lux hours.



For what they define as a medium responsivity object, their recommended maximum annual exposure is 150 000 lux hours so a single flash is about on millionth of this value. However, if the object is on display fo4 3000 hours per year. If you’re exposing it to 50 lux with the exhibition lighting, then 30 flashes per hour will roughly push you over their recommended limit by 10%.



For high sensitivity materials, they recommend a limit 15000 lux hours per year and if you use a very dim lighting of 30 lux for 500 hours of display per year then 18 flashes per hour would push you over the limit by 10%, which they suggest is very likely for a popular exhibit in a public museum.



They also point out the distraction for other visitors and the fact that flash photography with objects under glass would result in very poor images due to reflection.



Their medium category includes many historic plant colorings emphasizing alizarin in particular either as a dye on wool or as a lake pigment on any media; the color of most fur and feathers; and most chromogenic photographs with “chrome” in the name.



I know that Kodak used “chrome” in any reversal color including slides (Kodachrome and Ektachrome) and other companies seemed to follow suit. They also used it for their reversal color paper so chromogenic paper that you could directly print from a positive slide.



Their sensitive category consists of most plant extracts (most historic bright dyes and lake pigments on all media), insect extracts including lac on all media, most early synthetic dyes, many cheap synthetic colorants, most felt tipped markers (including black), pre-20th century tinting dyes for paper, and chromogenic prints with “colour” in the name.



Kodak used “color” for their negative/positive photographs so Kodacolor negatives were printed on Ektacolor paper.



-Doug

Douglas Nishimura

Image Permanence Institute

Rochester institute of Technology







From: Museum discussion list [mailto:[log in to unmask]] On Behalf Of Dan Bartlett

Sent: Thursday, March 03, 2016 2:02 PM

To: [log in to unmask]

Subject: Re: [MUSEUM-L] signage welcoming photography



I thought the flash question was laid to rest some time ago.

Selfie sticks on the other hand...

db





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