A screen grab of the spectra as processed by the software, showing raw intensity data, is in Figure 6.
The green line across the spectra shows the region plotted, and the dimmer lines above and below
the green central line show the range of pixels summed. Note that near reported wavelengths of
450 nm and 625 nm, the I0 spectrum can be seen to saturate. Wavelength calibration can be seen to
be terrible; methylene blue absorption is centered at 655 nm in a well‐calibrated measurement, but
turns up here at 590 nm (Figure 7). The reason for non‐calibration is clear from the way the
wavelength calibration is set; the user simply guesses which pixels correspond to the extreme
wavelengths emitted by the LED and detected by the camera, with no knowledge of the red or blue
cutoff of the sensor. If this were a "real" measurement, such arbitrariness would be unacceptable.
Here, it helps make the case for careful calibration, for showing the effect of the spatial extent of
the light source on dispersion and resolution. Saturation at blue wavelengths in both spectra and in
red wavelengths for the reference spectrum illustrates dynamic range limitations. Because these
spectra were taken in a darkened room, stray light is minimal. In a brightly‐lit room as shown in
Figure 4, stray light is also obvious