Martin Weberg wrote:
2010/2/8 Graeme Gill <graeme@xxxxxxxxxxxxx>:Martin Weberg wrote:For completeness, here we go again using v1.1.0. Notice the bump in plot 2 (St. dev. at 410nm is 0.2 (n=3)).It would be interesting to know how the bump is created, but without that paper to measure it is difficult to track down.Something I could provide, besides the paper?
Probably the spectrum of the paper measured without the UV filter will be enough.
readings contain no UV (10-400nm) I thought it was interesting that the Spectrolino fitted with UV filter produced higher reflectance thenwithout filter below 420nm.
On thinking about this some more, I can see only two possible explanations: 1) There is something different about the instrument calibration for UV vs. no UV filter. Measuring the calibration tile may reveal whether this is the case. 2) There's some level of up-conversion fluorescence, or similar going on. If it really is up-conversion fluorescence then this would be difficult to model, since it is typically non-linear (two-photon absorption), The "or similar" would have to be something like the high level of illumination at the fluorescent emission wavelengths suppressing absorption at shorter wavelengths. Fluorescence saturation may behave like this, but it is also non-linear and typically only happens at very high illumination levels. Graeme Gill.