[argyllcms] Re: Absolute light meter calibration?

  • From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 12 Aug 2015 19:27:02 -0700

On Aug 12, 2015, at 1:32 PM, Marwan Daar <marwan.daar@xxxxxxxxx> wrote:

Either way, it seems that you can't assume that all the input electrical
power is converted into radiant flux. And if this is the case, doesn't this
defeat the whole purpose of using a filament + mathematics to calculate
radiant flux, let alone irradiance (the latter requiring knowledge of surface
area)?

First, for the record, I've got a solution to the photographic project that
won't rely on any sort of absolute measurement and will instead make use of
data that an USGS astronomer has generously agreed to supply me with when I'm
ready.

But I still think this may well be a fun and perhaps-worthwhile project to
experiment with.

It seems a bolometer is going to be unavoidable.

I'm also starting to think that it might be prudent to make my own bulb. Can't
be <i>too</i> difficult, can it? Especially if I use something like a canning
jar for the bulb. That would permit me to use a piece of tungsten (or maybe
some more modern alloy?) whose physical dimensions I'd have complete control
over -- make it nice and big and wide and flat, such that I can assume that the
light is going 50% / 50% straight out the front and back with negligible
amounts to the top, bottom, and sides.

As for the question of emissivity...would lamp black suffice for making the
filament be close enough to a black body as makes no difference? Is there
anything more modern that might be better?

It's going to be something of a back-burner project, but I'm pretty sure I'll
have a lot of fun with it. And, who knows? Maybe I'll work out enough kinks to
create a "good enough" low-cost design that others will find useful....

b&

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