I wonder if you could do something with a bolometer. For example, a
bolometer with an optical window. You don't actually place the light
source inside the bolometer (so you don't measure heat output), but
you make sure all of the light from the source enters the bolometer
and hits a set of targets which ensure, say, 99% absorption.

There may also be detectors which have very well known quantum
efficiencies (i.e., electrons out per photon in).

Sean


On Sun, Aug 9, 2009 at 1:24 PM, Robert A. LaBudde<ral@lcfltd.com> wrote:
> I realized recently that I have no idea how an absolute measure of
> radiant light power at even a single fixed wavelength can be made.
>
> E.g., suppose you have an LED at 620 nm center frequency and you want
> to measure power output. How do you do this?
>
> It is easy enough to construct a detector system that gives a result
> proportional to power, but how do you scale that measurement to
> absolute radiance?
>
> The typical approach is to use a NIST (e.g.) traceable light meter
> and calibrate your meter to it. But how does NIST calibrate the meter
> in the first place?
>
> Are there standard light sources that provide standard radiant powers
> for known current inputs? Or are there detectors that can read
> absoluted received power?
>
> Some googling did not reveal answers to these questions.
>
> In the olden days, at least we had a standard candle to use!
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
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> Robert A. LaBudde, PhD, PAS, Dpl. ACAFS =A0e-mail: ral@lcfltd.com
> Least Cost Formulations, Ltd. =A0 =A0 =A0 =A0 =A0 =A0URL: http://lcfltd.c=
om/
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