On 25 October 2010 23:09, Gerhard Fuernkranz <nospam456@xxxxxx> wrote: > Am 25.10.2010 22:22, schrieb Graeme Gill: > > Whether that is of any significance, depends on your context. If it is > > of no consequence to you, then I guess purchasing an instrument with 1 > > nm resolution is not on your agenda :-) [Note that I currently have no > > means of verifying whether the above differences represent an > > improvement in accuracy of not.] > > Hi Graeme, > > looking at your laser pointer spectral plots it seems that the FWHM of > the instrument's optical system is still the limiting factor [hard to > tell exactly from the diagram - but I'd guess about 20nm ? - assuming of > course that the laser is really monochromatic] The benefit of higher > sampling resolution is of course limited if the bandwidth cannot be > reduced as well. Theoretically the higher sampling resolution should > offer an opportunity do deconvolve to a smaller effective bandwidth, but > in practice a stronger deconvolution is limited either, by a too bad S/N > ratio. Certainly, as we see, high-res mode does reduce the effective > FWHM, but obviously it can't reduce the effective BW by the same factor > as the sampling resolution is increased. So I'd still expect a > noticeable improvement from an instrument which reports not just with > 1nm resolution, but also *with 1nm FWHM*. According to the literature, > 20nm BW is too much for accurate measurement of narrow-band light > spectra, the literature rather suggests to use a BW of 5nm or less (and > a corresponding resolution too, of course). To get a feeling for the > impact, it's quite easy to simulate how the effective spectrum locus > moves in chromaticity space, when monochrome spectra are "broadened" to > a triangle or Gaussian with say 5nm, 10nm, 20nm, etc. FWHM [see > http://tinyurl.com/ykrms2], and it should be easy as well to compute the > corresponding colorimetric errors. > > Regards, > Gerhard > That's a very interesting diagram you linked to there! I do wonder how much processing instruments like the i1 do before reporting the spectral data. Unfortunately I don't have a line source sufficiently close to 520nm to tell properly how close a result it's giving. Incidentally, I have re-assessed the LED spectra I measured, and I was wrong. There is indeed a difference between hi-res and standard mode at 650nm. The difference appears as a shift along the spectral locus towards green when switched to hi-res mode. I calculate it at about 9dE (1.7 dE94). Who knows which is the real answer? The sp files if anyone is interested: (intensity was not controlled between measurements) http://www.satsumatree.co.uk/redlaser_s.sp http://www.satsumatree.co.uk/redlaser_h.sp http://www.satsumatree.co.uk/greenlaser_s.sp http://www.satsumatree.co.uk/greenlaser_h.sp Sam Berry www.satsumatree.co.uk