This is my Project STAR spectrometer. It was very inexpensive.
I use it for examining the color of different lights inside and outside. (Don’t look directly at the sun through this device – or anything else!)
It works by taking in light via the small opening at the upper-right.
The light bounces off the diffraction grating at the bottom of the photo.
It then spreads out over the graduated scale, which is inside the curved feature at the top of the photo.
I view the scale through the eyepiece that’s at the bottom of the photo.
I don’t get a histogram showing relative wavelength intensity, but it’s really easy to see what wavelengths are strong or weak, or which ones are missing.
I love having this!