Cardboard Spectrometer, Rainbows in Your Pocket

Maybe you had noticed that different light sources give a wide variety of sights and sensations, especially due to colors revealed by illuminated objects. It can be true that some very nice pieces of furniture bought in a well lightened showcase, or a jewel which glittered with beautiful rainbow colors, are not so spectacular whenever you took them in your living room... let's understand together why it's so.

The spectrum of a light is the whole variety of colours which are emitted from that light source. Rays emitted can also be invisible to human eye, some can be heat, others can be different types of electromagnetic radiations. But for now we only wish to see juicy tints from any light source we run into, and wonder about how much variety of colours is in a single lamp. This could also make us thinking deeply about lighting choices for our cities and our house.

The spectrum you see in this instructable's first step comes from a fluorescent neon light, and indeed you can distinguish coloured lines detached one each other. Looking into an incandescent light, you will see that things are different, and also solar light, LED for plants growing, sodium lamps, and so on.

Spectrometers have different working principles. You can see the spectrum with a glass prism, with a diffraction grate, but also with a vynil record or a Compact Disc. If you look a light while reflecting on a CD you will see some beautiful colours of the rainbow. This is already a cool toy, but it needs some better setup to become a semi-professional spectrometer.

We will actually use a CD which I hope you already have in your scrap. You also need some cardboard tubes, but pvc pipes are also good. Personally I love the surface of these cardboard tubes I found somewhere, it's smooth and can be easily sanded with sandpaper.
Then keep close at hand some adhesive tape and a piece of iron wire.
My project expect you to design and 3D print covers for the tube, but if you don't own a 3D printer don't worry, you as a good maker will have no difficult to adapt some plastic caps.

You will be surprised to see how much simple this project is.
The viewfinder is nothing more than an hole distant about one inch from the edge. Use a drill if the cardboard is quite thick, but maybe you can manage it with a different tool. Then make it rounded and smooth with a little roll of sandpaper.
The reflector is the piece of CD-rom, just cut it like a slice of cake. The width shall be just a bit more than inner diameter of the tube. Embed this CD slice inside the tube, just under the hole, with the reflecting surface looking the hole, and an angle of about 35-40°, you will now the right angle when you will see a rainbow while looking into the hole. When you are pretty sure you can glue the piece of CD in place.

The cap will have to rotate freely but also to stay in place. To obtain that, shape a piece of iron wire on the cardboard tube so to make a big ring, then fix it at about 1cm from the edge at the opposite side of the viewfinder, with some amount of well thighten electric tape.

Those are anything special... just a pair of caps, one with a slit. You can obtain them maybe from milk bottles, just cut a 1mm wide slit in center of one. Then adjust the iron ring and number of tape turns around the ring to obtain a perfect joint. You can also glue them in place but I don't suggest it. The rear caps is simpler to draw since it doesn't need a slot even a slit.
Anyway, if you own a 3D printer it's time to make something cool. Use a 3D software to design caps like in the pictures, with right diameters to get stuck around the ring and the tape. I used Rhinoceros but any software will be fine since it's a very simple shape. Please refer to other instructables to know something more about slicers and printing parameters.

When you have both caps you can simply embed them in place. The front top also rotates so you can see different effects when light comes directly through the slit, just point the tube toward the light and look into the hole.