Wow, this is so great to see very close to @stoft's post: https://publiclab.org/notes/stoft/04-14-2016/spectrometer-stability

Were you able to assess intensity stability over time? See @stoft's post for his approach to measuring intensity stability.

Great post, thanks!

Yeah I had a look at stoft's post and was very impressed about his orderly and organised way of doing things. I built my spectrometer 3 weeks ago and was basically playing around with it at first before I wondered how good a cardboard apparatus really can be and how reproducible it's data really are. I must admit, so far I am pretty impressed by this low-cost science. The velcro design did not look too promising at first, because the tension on the webcam wire lifted the webcam up a bit thus changing the angle between dvd grating and camera. The double sided sticky tape also did not hold the camera in place, so I used single sided sticky tape and wound it around the webcam base. Then it bworked and I got my first spectra. And then I wanted to find out more. I read some of stofts posts about stability issues and started my own tests. How does the RGB thing work, what kind of sensors are we using, where is always the yellow gone...? One problem is I don't have many lamps to choose from at the moment, esp. not a super-stable Solux. But although I had a 7 nm peak wavelength "wobble" here in IR spectra over time, I was very impressed by the CFL lamp test with almost matching curves:

But I must admit that I was more looking for the peak wavelengths than for the intensities because the places of the peaks usually are the fingerprints (for material spectra) not the heights.

I will have another look at stofts statistics to see if I can evaluate my data more in-depth. And now that the time-lapse capture macro is working I might do some more tests.

What I would like to find out one of these days is, how often we have to re-calibrate the spectrometer - every week? Once a month? Only once? The longterm drift in wavelengths over weeks or months would be interesting. But that would mean to set up the thing and leave it untouched for the whole test period. Absolutely stable environment conditions (no displacement of the apparatus, regular light source pre-heating, light ray angle stability, stray light prevention, vibration prevention, temperature stability and so on...) over weeks to capture maybe one spectrum a week or so. Then calibrate all the spectra with only one calibration spectrum and look at the differences. I guess it could be interesting for the oil testers here, too. And of course, it would be great if anyone who can get hold of a Solux could re-do stoft's tests and statistics to see if the results are the same in Australia or the Phillipines. Because thats exactly what would make a oil pollution database workable: different spectrometers producing the same "fingerprint evidence". Perhaps you could even exchange or pass around some oil samples to as many spectrographers here in the forum as possible and compare the results.

Great questions. I do think @stoft is mostly interested in intensity stability for the moment but both are good questions.

I'm interested in whether the stability of the solux is unique or if all incandescent bulbs are that stable. Or if the 12v power source @stoft is using is relevant.

The last point would be easiest to test: test a no-brand lamp with the same setup and the same power source and do the same stats on the results.