Indigo (Paperback)

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Indigo is the color on the electromagnetic spectrum between about 420 and 450 nm in wavelength, placing it between blue and violet. Although traditionally considered one of seven divisions of the optical spectrum, modern color scientists do not usually recognize indigo as a separate division and generally classify wavelengths shorter than about 450 nm as violet. Like violet, whether indigo is considered a shade of purple depends on context. Common English usage defines purple as any color between red and blue whereas in color theory, purple is defined as any non-spectral color between violet and red. Thus indigo and violet fit the common but not the color theory definition of purple. One can see spectral indigo by looking at the reflection of a fluorescent tube on the underside of a non-recorded compact disc. This occurs because the CD functions as a diffraction grating, and a fluorescent lamp generally has a peak at 435.833 nm (from mercury), as is visible on the fluorescent lamp spectrum.