Path: utzoo!attcan!uunet!decwrl!mcnc!rti!dg-rtp!bigben!bigben!philip From: philip@beeblebrox.dle.dg.com (Philip Gladstone) Newsgroups: sci.space Subject: Re: The great light bulb debate Message-ID: Date: 11 Nov 90 22:08:38 GMT References: <9011092213.AA05755@cmr.ncsl.nist.gov> Sender: usenet@dle.dg.com (Net News) Organization: Data General, Development Lab Europe Lines: 40 In-Reply-To: roberts@CMR.NCSL.NIST.GOV's message of 9 Nov 90 22:13:28 GMT In article <9011092213.AA05755@cmr.ncsl.nist.gov> roberts@CMR.NCSL.NIST.GOV (John Roberts) writes: >Modern light bulbs are filled with argon, not vacuum. (Expensive ones >use krypton.) As you imply, the old bulbs were evacuated. I believe the main reason for the switchover to inert gas was to reduce the rate of evaporation of the filament at a given temperature. In the UK (10 years ago) light bulbs contained *some* gas to about 30% atmospheric pressure. This is easy to demonstrate by following this procedure: 1) Find a light bulb -- preferably a dead one (it'll be useless if you complete the rest of these instructions). 2) Fill a bucket with water. 3) Find a compass (the drawing instrument) or other sharp spiky object. 4) Use the compass to make a small hole in the metal cap of the bulb. 5) Hold the bulb under water and push the compass into the metal cap and wiggle it around inside. If you do this just right, you will break the glass seal that was used to evacuate the bulb. 6) The water now rushes in to equalise the pressure. You can now judge what the pressure was before you broke the seal by how much water entered. WARNING: If you do this wrong you could break the envelope. For this reason wear gloves. -- Philip Gladstone Development Lab Europe Data General, Cambridge England. +44 223-67600