Talk:Luminous intensity

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[edit] Circular

Is it just me, or does this cluster of articles define lumen in termas of candela and candela in terms of lumen?—The preceding unsigned comment was added by 206.165.217.125 (talk • contribs) .

It's just you. "One candela is defined as the luminous intensity of a monochromatic light source of frequency 540 THz...which has a radiant intensity of 1/683 watts per steradian." I'll change "which" to "that" to make it sensible. Dicklyon 22:42, 31 July 2006 (UTC)

But doesn't that still define intensity in terms of intensity? Larklight (talk) 19:23, 14 May 2008 (UTC)

No. Luminous intensity and radiant intensity are two different things. It is not defining one in terms of the other anyway. It is an operational definition. What it does is it describes physically how to make a light source that you know emits one candela of luminous intensity. The candela is an SI base unit, so it is defined by experiment rather than directly referenced to other SI base units. The definition says that if you take a light source that emits monochromatic 540 THz light, and adjust it so its radiant intensity is 1/683 watts per steradian, the source's luminous intensity will be one candela. --Srleffler (talk) 22:51, 14 May 2008 (UTC)

[edit] SI

Why is this an 'SI base unit' ? Perhaps the article could explain.—The preceding unsigned comment was added by 70.225.166.87 (talk • contribs) 20:11, October 19, 2006.

The SI base units were chosen to give a complete set of physical quantities that can be precisely measured, so that the definitions of the units are precise. The explanation belongs at SI base unit, and this article does provide a link there.--Srleffler 02:19, 20 October 2006 (UTC)

One of the things that distinguishes the base units from other units is that their definitions are operational. The base units are not directly defined in terms of other units, but rather are defined by a description of a physical process that would produce exactly one unit of the specified quantity. --Srleffler (talk) 23:18, 14 May 2008 (UTC)