Summary

This easy to build hand-held spectroscope helps you to experiment with different light sources and understand the visible spectrum.
Follow the quick guide in order to build your own in less than 1 minute (plus printing time).
Read below to see a quick overview of the physical principle of the device.
GUIDE: https://youtube.com/shorts/uCRv-SgAUA0

How I Designed This

DVD data is stored in circular lines, each one separated by 0.74 micrometers. This acts as a diffraction grid (we do not consider the curvature of the disk, nor the separate bits). The light that traverse the grid gets split depending on its wavelength. This can be calculated with optics calculations, in order to know where the light maximums will be. Every color has a maxima in the center (as if the light didn't get scattered, and then the second maxima (the one we see through the apparel). The position of the maxima depends on the color, so each color is separated.
This is a very crude explanation, feel free to ask for more info or search online.

More complex spectroscopes work by refraction grating, using the grid as a mirror rather than a transparent film. This proved to be more difficult in the "low-cost and compact" scope of the project, but I might develop a design on this concept.

Here we can see the data lines we use as a diffraction grid. DVD and CD have similar structures, but different sizes, and that's why DVD can hold more data in the same space.

Spectroscope DIY