The bolometer idea does seem to be a possibility. I had forgotten about that. But how do you calibrate a bolometer? :) At 03:43 PM 8/9/2009, Sean Breheny wrote: >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 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! > > ================================================================ > > Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: ral@lcfltd.com > > Least Cost Formulations, Ltd. URL: http://lcfltd.com/ > > 824 Timberlake Drive Tel: 757-467-0954 > > Virginia Beach, VA 23464-3239 Fax: 757-467-2947 > > > > "Vere scire est per causas scire" > > ================================================================ > > > > -- > > http://www.piclist.com PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > >-- >http://www.piclist.com PIC/SX FAQ & list archive >View/change your membership options at >http://mailman.mit.edu/mailman/listinfo/piclist ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: ral@lcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causas scire" ================================================================ -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist