Australians set shining standard


	Australians set shining standard

pokkets

7-16-2008 5:47 PM

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pokkets says:

They originally described the candela as the amount of light emitted by the average? candle. Since the definition has become more precise, but measurement is still improving. Here's the exact definition (for anyone that cares-don't ask me what a steradian is) from wikki:
Since the 16th General Conference on Weights and Measures (CGPM) in 1979, the candela has been defined as:
The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

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<div style="margin: 12px 0px; font-family: arial; color: #333333; background: #ffffff; border: solid 4px #e5e5e5; width: 100%; clear: left;"><div class="CM_CTB_Content_Wrap" style="margin: 0px; padding: 0px;background-color: #ffffff;"><div style="border-bottom: solid 1px #dcdcdc; white-space: nowrap; margin-bottom: 8px; background-color: #eeeeee ;background-image: url(http://clipmarks.com/images/source-bg.gif); background-repeat: repeat-x; height: 24px; line-height: 24px; vertical-align: middle; padding-bottom: 4px; color: #666666; font-size: 10px;" ><a href="http://clipmarks.com/clip-to-blog/" title="see clips that are hot right now"><img src="http://content.clipmarks.com/blog_embed/dc02adf6-9d42-45e9-9c63-412244ddc20d/33802EEF-C6BE-441E-A73D-A7445232F00E/" alt="" width="19" height="19" border="0" style="vertical-align: middle; margin: 0px 4px; display: inline; border: none; float:none;" /></a>clipped from <a title="http://www.abc.net.au/science/articles/2008/07/16/2305348.htm?site=science&topic=latest" href="http://www.abc.net.au/science/articles/2008/07/16/2305348.htm?site=science&topic=latest" style="font-size: 11px;">www.abc.net.au</a></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.abc.net.au/science/articles/2008/07/16/2305348.htm?site=science&topic=latest"><P>Errol Atkinson and colleagues from the <A target="_blank" href="http://www.measurement.gov.au/">National Measurement Institute</A> have refined the measurement of the candela, the basic unit of brightness, to eliminate all but 0.1% of uncertainty. </P></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.abc.net.au/science/articles/2008/07/16/2305348.htm?site=science&topic=latest"><div align="center"><img src="http://content6.clipmarks.com/blog_cache/www.abc.net.au/img/3330D233-251A-43A5-9D91-A6CCF7D1B9E0" alt="burning candle" /></div></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.abc.net.au/science/articles/2008/07/16/2305348.htm?site=science&topic=latest"><P>They set the standard by measuring the light from a mercury-xenon lamp shone through a set of filters, and finally through a small 5 millimetre aperture in a piece of metal.</P></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.abc.net.au/science/articles/2008/07/16/2305348.htm?site=science&topic=latest"><P>"These light sources have a very consistent light output," says Atkinson.  It was using them that allowed the institute to reduce the potential error in its standards to 0.1%.</P></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.abc.net.au/science/articles/2008/07/16/2305348.htm?site=science&topic=latest"><P>The candela plays an important role in defining international lighting standards, and is used for a wide range of applications from household light bulbs, through to techniques to identify faults in the manufacture of jet engine components.</P></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.abc.net.au/science/articles/2008/07/16/2305348.htm?site=science&topic=latest"><P>Atkinson says that because the amount of light coming out of a substance is also closely linked to its temperature, the advance could lead to a change in the way the SI standard for temperature is defined. </P></blockquote></div><div style="margin: 0px 6px 6px 4px;"><table style="font-size: 11px;border-spacing: 0px;padding: 0px;" cellpadding="0" cellspacing="0" width="100%"><tr><td style="background:transparent;border-width:0px;padding:0px;">&nbsp;</td><td align="right" style="background:transparent;border-width:0px;padding:0px;width:107px" width="107"><a href="http://clipmarks.com/share/33802EEF-C6BE-441E-A73D-A7445232F00E/blog/" title="blog or email this clip"><img src="http://content7.clipmarks.com/images/c2b-foot.png" border="0" alt="blog it" width="107" height="17" style="border-width:0px;padding:0px;margin:0px;" /></a></td></tr></table></div></div>

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