Rainbow Symphony Diffraction Gratings Slides - Linear 500 Line/Millimeters, Package of 25 Makes the study of light and color fun and unforgettable Features highly efficient embossed Holographic Optical Elements Used for the direct viewing and analysis of spectra from different gas tubes and other light sources Spectrum produced from our gratings is the brightest possible with a minimum of distracting visual noise Great for overhead projector or 35mm slide projectors