[visionlist] Reference Source

Jenny Read J.C.A.Read at ncl.ac.uk
Mon Apr 14 07:14:34 PDT 2008

I assumed Mark was wanting a light source of a known luminance, to check 
the numbers output by his photometer. I don't have any knowledge to 
offer, but I get my photometer calibrated at Optical Test and 
Calibration Ltd, http://www.otc.co.uk/, and assume they or a similar 
company would be able to provide more information if you were to 
approach them...

Best wishes,


Nils T Siebel wrote:
> Dear Mark,
> If you are looking for a reference for the definition of "luminance"
> and other terms in video/TV technology the CIE recommendations (e.g.
> 601, 709)  are the definitive sources.  In a more practical sense the
> following text is a very good source of information, with formulas
> etc. (the CIE recommendations are also cited and explained there):
> @Misc{FordRobe98,
>   author =       {Adrian Ford and Alan Roberts},
>   title =        {Colour Space Conversions},
>   howpublished = {Available at \url{http://www.poynton.com/PDFs/coloureq.pdf}},
>   month =        {August},
>   year =         1998
> }
> Charles Poynton's colour home page at
> http://www.poynton.com/Poynton-color.html is a good starting point for
> more information.  His colour FAQ is a very good source, too.
> >From the colour FAQ:
> "3. What is luminance?
> "Brightness is defined by the CIE as the attribute of a visual
> sensation according to which an area appears to emit more or less
> light. Because brightness perception is very complex, the CIE defined
> a more tractable quantity luminance which is radiant power weighted by
> a spectral sensitivity function that is characteristic of vision. The
> luminous efficiency of the Standard Observer is defined numerically,
> is everywhere positive, and peaks at about 555  nm. When an SPD is
> integrated using this curve as a weighting function, the result is CIE
> luminance, denoted  Y.
> "The magnitude of luminance is proportional to physical power. In that
> sense it is like intensity. But the spectral composition of luminance
> is related to the brightness sensitivity of human vision.
> "Strictly speaking, luminance should be expressed in a unit such as
> candelas per meter squared, but in practice it is often normalized to
> 1 or 100 units with respect to the luminance of a specified or implied
> white reference. For example, a studio broadcast monitor has a white
> reference whose luminance is about 100  cd*m -2, and Y  =  1 refers to
> this value."
> Hope this helps,
> Nils.
> On Wed, Apr 9, 2008 at 9:25 PM, Dr. Mark Brady <mark.brady at ndsu.edu> wrote:
>>  Dear Colleagues,
>>  Does anyone have any suggestions for a luminance reference source for use
>> in calibrating photometers?
>>  Mark J. Brady
>>  Department of Psychology
>>  North Dakota State University
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Dr Jenny Read                               Office: +44 191 222 7559
Royal Society University Research Fellow    Mobile: +44 794 401 5796
Institute of Neuroscience,                  Fax: +44 191 222 5227
Faculty of Medical Sciences,    	    mailto:J.C.A.Read at ncl.ac.uk
Newcastle upon Tyne, NE2 4HH, UK.           http://www.staff.ncl.ac.uk/j.c.a.read

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