Rich, Peter, Strobe flash is not a simple calculation. The iris of the eyes and 'visual purple' both alter the sensitivity. So human susceptibility depends on darkness of the environment.
Strobe flash units are rated in 'Watt-seconds' but many flash units have a thyrister circuit that cuts off the flash after a short duration. Amateur cameras have 'pre-flash' that causes the iris to close to avoid 'red eye'. Then there is a distance-to-subject factor, etc. At 2" distance, amateur flash units can be deadly. Professionals use high-powered units for group shots, but the distance to subject is much greater so the effect on the subject is reduced. Professionals using color film prefer slow flash durations <1/2000 sec because the color balance of the film is subject to reciprocity failure. Some professionals use a dark studio so that the eyes of the subject appear larger (as the iris opens), and of course, no pre-flash. But pros use 2- and 3-light set-ups; flash units are not directed at the eyes (as with amateur photographers using 'flash-on-camera'. Flash exposure is becomming less of a problem as professionals shift to digital cameras. The computerization will keep the flash intensity minimally above ambient illumination so that the subject is not harmed by the light flash. David Sterner Member of American Photographic Historical Society and IEEE -----Original Message----- From: Rich Nute [mailto:[email protected]] Sent: Friday, October 19, 2001 4:00 PM To: [email protected] Cc: [email protected] Subject: Re: Light Emission from Professional Photography Flashes Hi Peter: > Any limitations/requirements for amount of light emitted from professional > photography flashes? Any UL, IEC or European standards which specify > limitations? > > I know how many you like being photographed - but imagine what harm one of > these flashes can cause to your eyes! The root question is what is the maximum safe optical energy as a function of time for the eye? I suspect there are many research documents for this eye parameter. Check out this optical radiation safety calculator: http://vision.arc.nasa.gov/personnel/jbm/home/exps/java/safe_txt.html The calculator is described for situations such as when the eye is illuminated for photography. I suspect this is for steady- state and not for flash. But, it should provide some references. Good luck, and best regards, Rich ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
