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Foot lamberts to foot candles


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#1 G McMahon

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Posted 23 February 2007 - 10:23 AM

Hello all.
Is there a correlation between foot candles and foot lamberts. It may seem archaic, but I am getting used to the idea of using foot candles (I find it handy lighting video), but that doesn?t help me when it comes to spot metering.

Does it work like foot candles too, 4FC is half the light of 8FC?

Thanks,
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#2 Sam Wells

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Posted 23 February 2007 - 11:24 AM

http://en.wikipedia....ki/Foot-lambert

note the first paragraph.

Really the only time I have used Foot-lamberts is in mesuring screen brightness for film projection.
(I have a Sekonic spot meter that will read in FtL from a reflective spot measurement.

NB acceptance window with a "chopped" light source such as a film projector might not be optimal - I haven't investigated, but it seems to "good enough for .gov work" !

-Sam
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#3 Jim Feldspar

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Posted 23 February 2007 - 01:20 PM

http://en.wikipedia....ki/Foot-lambert

note the first paragraph.

Really the only time I have used Foot-lamberts is in mesuring screen brightness for film projection.
(I have a Sekonic spot meter that will read in FtL from a reflective spot measurement.

NB acceptance window with a "chopped" light source such as a film projector might not be optimal - I haven't investigated, but it seems to "good enough for .gov work" !

-Sam


If I understand that first paragraph correctly, then the number of footlamberts you get with
a spotmeter is equal to the number of footcandles? It says that the number of footlamberts
is equal to the incidence illimination of footcandles but footcandles are footcandles, right?

It's not like a meter that gives you an f stop but has to be interpreted depending on whether
you took
a reflected or incident reading, is it, despite the that text's use of incidence ?
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#4 Mark Dunn

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Posted 24 February 2007 - 06:44 AM

The intensity of a luminaire at a given distance is measured in footcandles, the brightness of an illuminated surface in footlamberts, IIRC. So FC are measured incident, FL reflected. IIRC.
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