A spectrum (plural spectra or spectrums[1]) is a condeetion that is nae leemitit tae a specific set o values but can vary infinitely within a continuum. The wird wis first uised scientifically within the field o optics tae describe the rainbow o colours in veesible licht when separatit uisin a prism; it haes syne been applied bi analogy tae mony fields ither nor optics. Thus, ane micht talk aboot the spectrum o poleetical opinion, or the spectrum o activity o a drug, or the autism spectrum. In these uises, values within a spectrum mey nae be associatit wi precisely quantifiable numbers or defineetions. Such uises imply a broad range o condeetions or behaviors grouped thegither an studied unner a single title for ease o discussion.

The spectrum in a rainbow

In maist modren uisages o spectrum thare is a unifyin theme atween extremes at either end. Some aulder uisages o the wird did nae hae a unifyin theme, but thay led tae moden anes through a sequence o events set oot ablo. Modren uisages in mathematics did evolve frae a unifyin theme, but this mey be difficult tae recognize.


  1. Dictionary.com. The American Heritage Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. (accessed: January 25, 2008).