[argyllcms] Re: Absolute light meter calibration?

  • From: Roger Breton <graxx@xxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sun, 09 Aug 2015 09:39:10 -0400

Hi Mark,

I, too, have an OceanOptics spectrometer but the colorimetry calculations
are wrong. And they're not interested in correcting their mistaking
software. I should never have spent that kind of money on this instrument
for color management purposes :(

/ Roger

-----Original Message-----
From: argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-bounce@xxxxxxxxxxxxx]
On Behalf Of Mark MacKenzie
Sent: 8 août 2015 10:40
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Re: Absolute light meter calibration?

Goof morning.

It sounds as if you want to be both specific and accurate. There have been
great strides made in making smaller, more portable more useable
spectrometers.

I use a modular spectrometer from Ocean Optics for a variety of purposes
from calculating the color of something, to change in color to monitoring
plasmas within glass chambers (this last one is a bit wild but a current
project). They have published applications for measuring emitting light
sources and it sounds very close to what you are trying to do.

There URL is: http://oceanoptics.com/
and one of their current specific applications is about measuring the visual
performance of pyrotechnics:
http://oceanoptics.com/video-ocean-optics-meets-le-maitre-pyrotechnics-and-e
ffects/

Here is an URL to their Light/Laser/Led Characterization section:
http://oceanoptics.com/applications/light-laser-led-characterization/

Hope this is of some help.

Mark MacKenzie,
Alcalde Wet Plate
New Mexico



On 8/7/2015 1:50 PM, Ben Goren wrote:

Nearly all photographic uses of light meters are ultimately geared towards
relative measurements of one kind or another. Nobody typically cares about
the _actual_ value for W/m^2 or Lux or what-not; just that, when the meter
says to set exposure for such-and-such a combination of aperture, shutter,
and ISO that the resulting photograph is what you expected.

I happen to, for the first time I can think of, have a use for getting a
truly accurate (within typical photographic margins of error, ideally less
than 1/3 stop) absolute measurement of local solar radiance. It's for an
esoteric project that might or might not pan out for making
colorimetrically-accurate photographs of the Moon and, perhaps, other Solar
System objects. The measurement would get combined with a spectrographic
measurement of the Sun and the ASTM E-490-00 extra-atmospheric solar
spectrum and all sorts of other math and what-not to, amongst other things,
eliminate the color cast caused by the atmosphere.

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?

It's both a photographic exercise and an excuse for me to do some hands-on
basic physics, so I'd welcome something, for example, suited for an high
school or college physics lab...but I _do_ want the final result to be
reasonably reliably accurate to no worse than 1/3 stop.

Thanks!

b&



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