brightline

or bright-line

[brahyt-lahyn]

adjective

(of rules, standards, etc.) unambiguously clear: This muddies the waters of what should be a brightline rule.

noun

Physical Chemistry. brightline spectrum.

Origin of brightline

bright + line¹

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for bright-line

Historical Examples of bright-line

But monochromatic or "bright-line" light is, by its nature, incapable of being so diffused.
A Popular History of Astronomy During the Nineteenth Century
Agnes M. (Agnes Mary) Clerke
Possibly all such stars have passed through a bright-line stage; but further evidence on the point is needed.
A Popular History of Astronomy During the Nineteenth Century
Agnes M. (Agnes Mary) Clerke