Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site ecsvax.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!whuxl!whuxlm!akgua!mcnc!ecsvax!dgary From: dgary@ecsvax.UUCP Newsgroups: net.physics Subject: Re: Thermonuclear Device Message-ID: <1143@ecsvax.UUCP> Date: Fri, 31-Jan-86 13:04:32 EST Article-I.D.: ecsvax.1143 Posted: Fri Jan 31 13:04:32 1986 Date-Received: Sat, 1-Feb-86 21:49:41 EST References: <8601182109.AA26118@s1-b.arpa> <497@anasazi.UUCP> <1080@mmintl.UUCP> Reply-To: dgary@ecsvax.UUCP (D Gary Grady) Organization: Duke U Comp Ctr Lines: 34 Keywords: photography, color temperature, black body Summary: Color temperature and black body radiation In article <1080@mmintl.UUCP> franka@mmintl.UUCP (Frank Adams) writes: [remarking on Will Fuller's observation that the Soviet Venera lander was subjected to temperatures on the order of the sun's surface] >This is not really very impressive. I believe a welding torch does the >same. Anything which is heated enough to glow white is at about solar >surface temperature. I believe you're correct. In fact, carbon arcs burn hotter than the surface temperature of the sun. In color photography (particularly cinematography) it is not unusual to see "color temperature" meters that rate the overall color of incident light by comparison to the temperature of a black body emitting a similar spectrum. The meters are rated in degrees Kelvin. For incandescent sources (including light bulbs and the sun) they fairly accurately reflect the actual temperature of the glowing surface. For photographic floods the temperature is usually 3200 K or 3400 K (depending on the type). Arc lamps are around 5800 K. Of course, filtration can change the color temperature up or down without altering the actual temperature. You can buy blue frosted incandescent floodlamps rated at about 5800 K despite the fact that the filament's around 3200. A color temperature meter can read several hundred degrees hotter than the solar surface because of light from the blue sky. And a color temperature reading from fluorescent light is meaningless. Instead of an incandescent glow, fluorescent tubes produce light by a two-step process: A gas discharge (like a neon sign's) excites a phosphor on the tube's interior, and the superimposed spectra of the two, riddled with spikes, resembles not at all the smooth hump of black body radiation. -- D Gary Grady Duke U Comp Center, Durham, NC 27706 (919) 684-3695 USENET: {seismo,decvax,ihnp4,akgua,etc.}!mcnc!ecsvax!dgary