This design is a mini spectrometer or spectroscope made with a 1000-line-per-millimeter plastic transmission grating. It requires a 2in. x 2 in. plastic grating that you can buy from Amazon. I made the mini spectrometers and gave them to my kids and friends, so I got the 10-piece pack: [https://www.amazon.com/dp/B0074R74D8](https://www.amazon.com/dp/B0074R74D8) . If you only need one, you can go : [https://www.amazon.com/dp/B0088AQFE4](https://www.amazon.com/dp/B0088AQFE4).

It is an easy print without needing support. However you need to print it in black filaments, prefer black matte or similar. I used the Midnight black filament from OVERTUNE.

What does it do

A spectroscope separates light into its component colors, or spectrum. In fact, if you google keywords like DIY spectroscope or CD/DVD spectrometer, etc., you will see many articles about how to make one. You may even see a design that is very similar to my design. The features of my design are:

1. It's easy to make. No crafting is needed, no blade to cut the DVD, so there are no worries about the knife slipping. Just print the model, buy a transmission grating, and assemble it. 
2. The angle of the window was optimized for the 1000/mm grating. 

Assembly is easy. The cap has three studs to hold the grating card and the tube. First, align the grating card and the cap so that the rectangle-shaped membrane and the view window are in the same direction (long side aligned; please use the photo as a reference), then insert the grating under the two studs and slide it into the cap. Then, align the spectrometer tube so that the slit is parallel to the short side of the grating membrane/view window. Then, slide the tube into the cap. You might need to apply some force – by design, it is a fairly tight fit. I want the spectrometer to be sturdy so you can carry it around and explore without worrying about falling apart.

How to use

Point the slit to the light source and look through the view window to the direction perpendicular to the window. Just like the puppy in the picture. It is a bit counterintuitive as people tend to look in the direction of the light source. You will see the slit in this case but not the spectrum.

Because it is possible to see the slit directly, please DO NOT point directly at the sun, UV lights, Lasers, or any light source that could be harmful to the eyes or your camera. Use the device responsibly! The creator of this project assumes no responsibility for any injuries, damage, or mishaps resulting from improper use.

Example spectrum

Sunlight: 

Point the spectrometer to the window, a white wall, or even the sky; you will see the spectrum of the sunlight. Again, please DO NOT point directly at the sun. Scattered light from the sky is sufficient for you to see the continuous spectrum of sunlight.

Fluorescent lights or compact fluorescent lights (CFL): 

These are the best objects to view with the mini spectrometer. Fluorescent lights contain a small amount of mercury vapor and an inert gas (usually argon) in the tube. When an electric current passes through the lamp, it excites the mercury atoms, causing them to emit light, including ultraviolet (UV) light. The inside of the glass tube is coated with a layer of phosphor powder. The emitted UV light strikes the phosphor coating, which absorbs the UV energy and re-emits it as visible light. Different brands of fluorescent lights use different phosphor coatings, thus having different spectra. However, the most bright spectral lines will likely appear in them all. Among them, the violet-blue 436nm, the green line 546nm, and the yellow line 577/579 are from mercury. The two yellow lines are not distinguishable by the simple spectrometer. The cyan line is 488nm, coming from Argon. The bright red line is 611 nm from the Europium compound in the phosphor. 

CFL lights have this spiral shaped tubes, so they are easy to recognize. However, CFLs have largely been replaced by LED lights and are not as common as they once to be.  

Screens:

Nowadays, we are surrounded by all kinds of screens: phones, pads, TVs, and the little screens on all kinds of appliances. They can display different colors, so it would be interesting to observe them. For example, I included a picture of the spectra of my laptop showing red, green, blue, and white. Notice the different spectrum when the screen shows different colors.

There are much more lights waiting for you to explore. Enjoy!

Tip for taking photos of the spectrum

At this time, you might try using your phone to take photos of the spectrum. The first result might not be what you want :). Why? This spectrometer creates a mini dark room for spectrum viewing, and almost all today’s smartphone cameras will have a night mode or similar feature to boost exposure under dark conditions. This will result in an over-exposed picture with all the weak reflection and scattering light showing up, like a Christmas light show. So, you need to turn off the night-mode of your camera. I am using an iPhone, and it shows at the top-left corner. When the mode is activated, it is shown as a yellow button with the exposure time. You might even need to lower the exposure time manually. The spectrum will be in the center of the picture. So, focus only on the center and crop out the rest to get a good spectrum picture.

Don't worry too much about getting a perfect spectrum picture. It is designed to view the spectrum by eyes. As the old idiom says, “Seeing is believing.” No matter how many times you have seen the “perfect” spectrum in the books, it still feels fantastic when you point the little device to a light and see the spectral lines unfold before your eye!  Just explore around with the spectrometer. Look at the spectra of my laptop. The red part of the spectrum has two lines. I know that nowadays, the backlight of the LCD screen is usually LED, but I would never expect to see double lines for the red light.  There is always something new to learn :)