[argyllcms] Re: Absolute light meter calibration?
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Tue, 11 Aug 2015 07:39:59 +1000
Ben Goren wrote:
Can anybody suggest some sort of reliable way to get an accurate calibration
in
absolute units of either a typical Sekonic meter or an i1 Pro in ambient mode
or
something like that? I'm thinking, ideally, of a way of creating a light
source of
dependably-known illuminance that I can measure. An unfrosted incandescent
bulb, maybe?
And some way of verifying that the wattage printed on the bulb matches what
it's doing?
And the math to calculate the rest?
I'm not sure there is any cheap way. The meters are all calibrated during
manufacturing,
yet my experience is that their absolute calibration is not very consistent.
Trying to get consistent absolute levels in measurement is also a challenge -
slight
changes in measurement geometry seem to result in very noticeable changes in
values.
So I have my doubts that a do-it-yourself approach is worth more than relying on
how an instrument was factory calibrated, because what is the worth of such a
calibration if you have no way of verifying the reference ?
It is expensive to obtain a traceable reference source i.e. :
<
http://oceanoptics.com/product/hl-2000-cal-family/>,
<
http://oceanoptics.com/product/dh-2000-cal-family/>,
<
http://www.newport.com/Calibrated-Sources/378236/1033/info.aspx>,
<
http://www.avantes.com/products/light-sources/item/947-avalight-hal-cal-mini-dh-cal-calibrated-light-source
and they don't last very long (typically 50 hours).
The best path may be to send your instrument to someone who has a reference
source
to calibrate it against.
Graeme Gill.
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