Instructional note: Spectrometers made from boxes and CDs were used. Both the continuous solar spectrum and a discrete fluorescent light spectrum were observed by the students.
Traditional colors of the visible spectrum in English: Red Orange Yellow Green Blue Indigo Violet. Indigo was apparently inserted by Newton to have seven colors in the "rainbow" as opposed to six.
Below red: infrared heat radiation. Microwaves. Radio waves. Alternating current.
Beyond violet: ultraviolet. Can cause sunburn, skin cancer. Even higher frequencies include x-rays and cosmic rays (cosmic radiation).
If gas discharge tubes are available, a demonstration of continuous versus discrete spectra can be done.
A rainbow is a continuous spectrum produced by the sun. All of the colors "blur" into the next color, there are no distinctive separations in the colors. The sun produces light as a result of being very hot. Things that produce light by getting hot produce continuous spectra.
A gas discharge tube contains one specific gas. Gases produce discrete spectra. The colors do not blur into each other but are separated by gaps where no color appears. Gases with a small atomic number such as hydrogen and helium clearly show separated spectral lines. The lines are related to the nature of the atomic structure of an atom. Atomic structure is a part of a later chapter in this text.