Public Lab Research note


Direct sunlight vs. diffuse sunlight...

by viechdokter | April 07, 2016 18:02 | 51 views | 11 comments | #12934 | 51 views | 11 comments | #12934 07 Apr 18:02

Read more: stable.publiclab.org/n/12934


viechdokter was awarded the Basic Barnstar by dhaffnersr for their work in this research note.


Today was a nice spring day here in Germany so I played a bit with my spectrograph. One minute there was full sunlight - the other minute the sun was hidden by nice white clouds. I took the two spectra to compare them. (Sorry, no calibration yet. I don't have a fluorescent lamp here at the moment.)

At first glance the two intensity curves are pretty similar. At least the overall appearance of the outline of the curves looks pretty much alike.

But if you look closer, you will see that the direct sunlight curve starts "earlier" (further into the blue/violet range) and ends "later" (further red). Some parts of the sunlight get swallowed by the clouds. There are certain intensity dips that are easier to see in the photos than in the curves. In diffuse sunlight a lot of yellow is missing, part of the turquois and violet. Some wavelengths (most of the green and blue) get through okay though.

In future, if I ever manage to calibrate the curves, I will theoretically be able to say what molecules cause which "curve dip" though my first guess would be that most of it will be due to water molecules...


11 Comments

comparison_direct_to_diffuse_sunlight_overlay.jpg

Here is an overlay of the curves.

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Hi! It looks like both of your spectra are clipping -- hitting 100% and flattening. You can learn a bit about how to avoid this here:

https://publiclab.org/wiki/spectral-workbench-usage#Overexposure

Also, subtraction is possible using the new Spectral Workbench 2 operations -- take a look!

https://publiclab.org/wiki/spectral-workbench-tools

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Hi Warren, thanx again for your input. Next time we get some sun I will try to work with reflective surfaces to reduce overall light intensity to avoid the overexposure. I guess the clipping of a single colour (for instance blue) will also affect the sum curve, won't it? I wasn't aware of that problem before I read your comment. Will be interesting to see, whether paper reflection changes the spectrum (i.e. absorbing colours...) Oh and thanx also for pointing me at the substraction of waves. Seems interesting. You know, I'm not a scientist and am just beginning to work with the spectrometer, but there seems to be a whole new world waiting to get discovered...

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No problem and good luck! Post again -- i'm sure others would love to see some ideas for reducing overall light level.

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comparison_direct_to_diffuse_sunlight_substraction_of_waves.jpg

Tried the substraction and yes, it does show the dips! Cool!

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hello! Very colorful spectra, you don't really have to be a scientist to see the beauty in those colors, amazing, isn't it? Your right , you have a whole world of discovery just waiting for you, good luck!

Dave H

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Thank you Dave. By the way, I had a look at your works and was very impressed. (Not that I would have understood most of it...) But one question came into my mind when I saw your setup: if you send the light through polymethylmethacrylate (however this molecule looks like) cuvettes - don't they also absorb light in certain (carbone/hydrogen) wavelengths? And if you use glass cuvettes - don't they absorb certain (silicate/oxygen) wavelengths? And how about the dilutant (water, alcohol, whatever...)? Do you create a "zero-spectrum" WITHOUT the actual agent you want to resaerch - i.e. only with the cuvette and dilutant in the light path - and then sustract the spectrum from the one you get WITH the agent?

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I am so glad that you asked that question! I use 2 types of cuvettes, 1) Quartz - they have neutral UV absorption, so it passes right on through without any artifacts or problems.

2) I also use semi-micro UV-transparent disposable Cuvettes, which are made of a plastic material that can be used with most polar solvents, very handy.

I have created my own "blanks" that I use to zero out the spectrometer, kind of a round about way of doing it, but it works, I usually subtract my reference, which usually is the solvent and then subtract the blank from that and it cleans up the signal pretty nicely.

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Okay, my sunlight did not show much UV because I let it shine through a glass window. Next time I will try without the glass. (Waiting for the next sunny day...) Not sure if that standard PLab-kit-camera can even detect UV... But that leads me to the next question: you seem to use a UV-Laser in some of your experiments. Is it right that it only uses a single UV-wavelength? That seems to mean that you only can explore matter that absorbs exactly THAT wavelength (and emitts perhaps a different one)? Is that right? What about "the other waves"?

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Hi, I think the glass in the camera lens and the sensor limitations may prevent much UV, even without a window.

When we use a laser, we're mostly trying to generate fluorescence from the sample. See https://PublicLab.org/wiki/oil-testing-kit

Hope that helps!

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Okay, now I understand. Thanx.

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