T.O. 33B-1-12-75When fluorescent materials are energized by ultraviolet radiation, visible light is emitted. The color of the emittedlight depends upon the material. Each type emits a specific wavelength ranging from violet (400 nm) to red (700 nm).Factors in selecting a fluorescent dye are the color emitted and the intensity of emitted fluorescent light. The mostfrequently used dyes emit a yellow-green light in the wavelength band of 510 to 560 nm. This color is chosen since thehuman eye has its highest response to wavelengths in the 550 nm range. Figure 2-27 shows the relative response of atypical human eye to various wavelengths of visible light under two different lighting conditions. Curve A at 100lumens (100 foot-candles) is typical of a well lighted inspection bench. Curve B at 2 lumens (2 foot-candles) is themaximum white light level allowed in a fluorescent penetrant inspection booth. Under the darkened condition, thesensitivity of the eye increases about 30 times and shifts slightly to the blue region. At a light level of 2 lumens, it ispossible for the eye to see some light wavelengths below 400 nm and above 700 nm.Figure 2-27. Relative Response of Typical Human Eye to Visible Light of Various Wavelengths.
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