This requires a "calibrated light source". How do you calibrate a light source? Nice PDF on LEDs and photometry. At 06:10 PM 8/9/2009, Stephen R Phillips wrote: >Try labsphere's website they have a nice article on it. >Here is there home page >http://www.labsphere.com/catdetail.aspx?id=227 > >This article appears to be one you might want to look at > >http://www.labsphere.com/data/userFiles/LED%20Measurement%20Guide.pdf > >--- On Sun, 8/9/09, Robert A. LaBudde wrote: > > > From: Robert A. LaBudde > > Subject: [EE]: How do you calibrate a light meter? > > To: piclist@mit.edu > > Date: Sunday, August 9, 2009, 1:24 PM > > 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