I recently got a DIY Spectroscopy Kit from PublicLab . I thought it would be nice to share my Build Log and subsequent spectroscoping most of the accessible light sources.I really loved when we used to work with the “Pro” versions of these in Physics 101 Labs.. I really never thought i could get one at home unless i built this.. This spectroscope is amazingly accurate as one of the tubelights i “probed” had almost identical manufacturers spectrum.. Wow

The kit came in a nice cardboard box and had everything you need to make your own spectroscope. It has:

  1. HD Webcam
  2. Flexible Cable for USB
  3. 45 degree cut wooden piece for fixing the cam.
  4. Good Quality Foam Tape
  5. A Water proof aluminium Conduit box
  6. A stencil/plan for the dark box
  7. DVD as a diffraction grating
  8. A very nice instruction manual
  9. Lots of Fun

The mystery box

Kit contents

Kit contents

Cutting the plans 
Box plans

Cutting the plansAssembling the Box

Make sure the inked/printed part stays outside. We dont want any reflections inside our dark room. Add the Foam Tape to secure the joints and add a piece of foam tape on the spot where its written “Bottom” . We will peel off the other end when we assemble all the components in the conduit.

Foam tape on bootom boxSplit Open the DVD

A DVD is a combination of two parts(actually many but we are concerned about two) . A Diffraction Grating is the heart of this device. We use the one made by a commonly available DVD. The reason is : (Source:Wikipedia)

“Ordinary pressed CD and DVD media are every-day examples of diffraction gratings and can be used to demonstrate the effect by reflecting sunlight off them onto a white wall. This is a side effect of their manufacture, as one surface of a CD has many small pits in the plastic, arranged in a spiral; that surface has a thin layer of metal applied to make the pits more visible. The structure of a DVD is optically similar, although it may have more than one pitted surface, and all pitted surfaces are inside the disc.”

So, take a small blade (in case you dont have big sharp nails) and try to apply force on the disk from the circular edge i.e the thin part and you will soon be able to separate both ends. Discard the shiny part and “cautiously” handle the second part. (No fingerprints)

Split open DVD

You can see this (Warning:PDF) for more on the calculations and preparation of grating part!

Now cut a sector of this disk and inspect it for fingerprints. Out of curiosity i applied some alcohol on the part with the intention to clean it but rendered it useless. So DONT use alcohol.

DVD diffraction grating

Next , cut a small portion from the farther end of the disk as tracks are more linear there.

Camera Time

The camera is a very beautiful circuit. Be careful with the USB cable provided its not that flexible as it looks.
The camera

Next mount the grating with the circular portion facing the camera. You also need to focus the camera by moving/unscrewing the upper black portion to about 9inches.

I advise aligning it a bit angled and not straight as shown.
Grating on the camera

Prepare the Mount

Now grab the piece of wood and stick foam tape on it as shown. Also use some tape on the sides for securing the wire for the USB camera.
Preparing the stand for camera

Now stick the camera unit on it and carefully stick the wire to the foam tape on the side. Be careful with the wire.

Assemble

Open the conduit box and stick the black box we made earlier by peeling off the tape..
Opening the Case

I suggest adding the extra foam tape to hold the box firmly in place.

Adding extra tape helps in securing the black box better

Now add the camera and slide the USB cable out. Carefully stick the wooden piece with the Foam Tape on its bottom to the conduit floor inside the region of the black flap.
Imaging slit
Now you need a Cable Tie to hold the wire in place and reduce the tension on the wire. A tape will do the job too, less aesthetically though.
Completed
Now screw the cover of the conduit back making sure you dont press on the webcam and start searching for a CFL (We have LEDs now 😛 )

Focus Shift

One thing that troubled me and i would suggest the designers of the kit is that the regulator on the camera heats up a lot and it worries me a lot.Also the USB cable is a bit small.I had to buy a extension cable to enhance the reach.

Calibrating

A CFL is needed to calibrate the build. Basically the wavelengths of certain peeks are known and using these we can calibrate the equipment ( Calibration to know standard- Instrumentation 101) .

So, go to spectralworkbench . Make an a/c so that you can save the data.Next go to begin capture and follow the instruction on screen. Point your scope to a CFL lamp and you will see a live feed on the webpage. Try rotating the scope till you get a bright sample and then move the yellow bar to the spot. Make sure you get green first and then red on your spectra when moving Left to right (ProTip) . If not you can click on flip button. When set click the “begin capturing” button.. and you can see all the stuff being done. When you are happy with a stable spectra click save and fill the form.

You will then be guided back to the site to calibrate. Once the spectra is saved you need to click the calibrate button and click as the dialog says (Be sure you are logged in or “Something went wrong” pops up).

After calibration you can see the wavelengths on the x-axis.

Here are some of my spectra:

blue

A blue LED from a STRIP

bulb

100W Phillips bulb. Extremely high IR content beyond 700nm

Bulbs are considered enormously inefficient as they emit large amount of energy they consume as IR which is not visible to human eye. Only a part of it is actually useful light. But camera’s do see IR . Check by seeing your remote’s Led thru your phone camera?
I always needed a proof of it ever since they taught this to me in 8th grade!
Here it is.

cyan

No wonder it contains Blue and Green

osram

The classic 6500k spectrum from my 40W OSRAM Tube Light

purple

Purple=Blue+Red

red

The pure RED Light from a LED

The spectrum peaks at 625nm. Using Plank’s equation, E=Hv
We have E=1.984V ! Wow.. The value of vf according to the datasheet is 2.1V Typical and 1.8V actual. That’s pretty close!

sunlight

Sunlight

You can see how vividly its true! The tubelight has a more peaky spectrum but the peaks are more or less aligned to the peaks/flats of the sunlight spectrum.

You also notice that sunlight has IR and UV content as well but tubelight doesnt!
Thats why people use sunscreen to protect them from UV!

The best thing about this web based UI is that it is crowd sourced so, If you click on Find similar you might get the same bulb brand or maybe material that somebody had tested. like i found a person/sample with almost same spectrum as i had. If he had given a much descriptive account of his bulb it would have been a lot useful

compIf you want to play around with Spectroscope without attaching it to webcam and just observe it with your eyes there is one by IUCAA here .

Check out the instructable here!

Cheers,

Rohit

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