Although each survey is held outside with the sun being the constant light source, the resulting spectrograph is satisfying every time - who doesn't love a rainbow?! Participants hold their cellphone camera to the spectrometer aiming toward the sun and snap a photo. It can be a keepsake of their interaction during a w|edge Survey and a way to share the experience via social media.
"The primary element in both spectroscopes and spectrographs is a narrow slit oriented perpendicular to the direction in which the grating or prism spreads the light. As with a pinhole camera, the small aperture images the light source sharply along the spectrum’s axis, which keeps the spread of wavelengths distinct. Each image of the slit, in a slightly different color, is arrayed across the field of view in a wide spectrum image. If any wavelength is brighter or dimmer than the rest, it shows up, respectively, as a bright or dark line in the spectrum."
This spectrometer was made combining a few different tutorials. This one had the greatest impact, and is also the source for the quote listed above: http://makezine.com/projects/make-24/high-res-spectrograph/