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Kids really enjoy this simple on-screen piano. Simply press a piano key or run your finger down the keys on a touch screen, to play the notes. Mouse users can click on the keys. The keys are in different bright colours and marked with the note they play.

Make a whole rainbow by mixing red, green, and blue light. Change the wavelength of a monochromatic beam or filter white light. View the light as a solid beam, or see the individual photons.