Prism with spectrum ray trace Intermediate 01/21/2014 Prism with tribeam Intermediate 01/21/2014 Iridescent clouds Intermediate 07/17/2013 iridescent cloud Intermediate 07/17/2013 Noble Gases Spectrum Intermediate 07/12/2012 Gas Discharge Tube Spectrum Beginner 07/12/2012 Oxygen Beginner 07/12/2012 Nitrogen Beginner 07/12/2012 Hydrogen Beginner 07/12/2012 Krypton Beginner 07/12/2012