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The Spectral Regions of Daylight which cause Fading
Author(s) -
McLaren K.
Publication year - 1956
Publication title -
journal of the society of dyers and colourists
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.297
H-Index - 49
eISSN - 1478-4408
pISSN - 0037-9859
DOI - 10.1111/j.1478-4408.1956.tb02125.x
Subject(s) - wavelength , daylight , visible spectrum , radiation , ultraviolet , optics , electromagnetic spectrum , absorption (acoustics) , materials science , optoelectronics , chemistry , physics
Organic colouring matters are faded by absorbed ultraviolet and visible radiation up to a critical wavelength, above which radiation is non‐actinic even if strongly absorbed. This wavelength is generally related to the normal light fastness of the colouring matter, “normal” referring to the substrate for which it was originally developed, e.g. vat dyes on cotton, disperse dyes on acetate rayon. The critical wavelength decreases as the resistance to fading increases, being in the red when the light fastness is 1–2 (minimum) and in the blue when it is 6–8 (maximum); there are, however, some exceptions to this rule. As long‐wave radiations preponderate in daylight and as the absorption bands are usually strongest in the visible spectrum, fugitive organic colouring matters are mainly faded by visible light, whilst those of high normal light fastness can in general be faded only by ultraviolet, violet, and blue light. The differences between the composition of actinic radiation constituting daylight and that emitted by the enclosed carbon arc have been shown to be relatively unimportant as a possible source of gross anomalies in light fastness testing based on comparison with light fastness standards. These differences do, however, render meaningless any attempts to equate one hour's lamp exposure with so many hours' sunshine.