Xref: utzoo sci.electronics:4734 rec.photo:4227 Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!mailrus!tut.cis.ohio-state.edu!rutgers!sunybcs!kitty!larry From: larry@kitty.UUCP (Larry Lippman) Newsgroups: sci.electronics,rec.photo Subject: Re: Flashbulbs (was something stupid and illegal...) Summary: The real facts about flashbulbs... Message-ID: <2929@kitty.UUCP> Date: 15 Jan 89 16:01:36 GMT References: <3835@midas.TEK.COM> <190700025@trsvax> <13355@cup.portal.com> <4622@sfsup.UUCP> Organization: Recognition Research Corp., Clarence, NY Lines: 55 In article <4622@sfsup.UUCP>, dcm@sfsup.UUCP (David C. Miller, consultant) writes: > In article <13355@cup.portal.com> mmm@cup.portal.com (Mark Robert Thorson) writes: > > > >At the risk of enormous flames, both here and hereafter, the fine wire inside > >a flashbulb is magnesium wire. > > If I remember correctly, the wire is simply aluminum and the bulb is > filled with pure oxygen. That way if the bulb is broken (either by > accident or intent) it is rendered harmless. All of this recent speculation about the composition of flashbulbs is interesting, but it is incorrect. The most common filament wire used in current flashbulb production is an alloy of tungesten and rhenium. Pure tungsten has been used in the past. Aluminum or magnesium wire would never be suitable for a filament; such wire is too soft or brittle for use as a filament, in addition to having too high a resistsnce for a 3 volt firing circuit. The filament is coated with a small amount of "primer" material, generally a perchlorate mixture. The combustible "filler" material inside a flashbulb is generally finely-shredded zirconium. Magnesium and aluminum have been used in past years for the filler material, but they do not possess the spectral power distribution that is today ideal for color photography. During manufacture, a flashbulb is evacuated and heated to drive out moisture (which is the #1 killer for flashbulb failure). The bulb is then filled with pure oxygen under pressure - typically around 100 psi. The bulb is then coated with a protective lacquer to entrain any glass should the envelope burst. This lacquer is also used for color correction purposes, which is why it is blue in color. Following lacquer coating, the bulb is then coated with an anti-static material (yes, flashbulbs can be discharged by static electricity, and in early years people were injured when a flasbulb would fire after just being touched). When current is passed through a flashbulb, the filament heats and ignites the primer. Particles of the primer rapidly propagate through the flasbulb, igniting the zirconium filler material, which then combusts rapidly in the atmosphere of pure oxygen. Those of you with photographic expiernce probably know that a flashbulb (like an AG1) typically reaches peak illumination in about 15 milliseconds, with the effective photographic illumination being extinguished after an additional 25 or so milliseconds having elapsed. In case you are wondering, the Magicube flash lamp used in the Instamatic X cameras are fired _mechanically_ by means of a torsion spring which causes a striker arm to hit a percussion primer. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {att|hplabs|mtune|utzoo|uunet}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"