T.O. 33B-1-1
2-74
c. All personnel performing any of the penetrant process steps SHALL be qualified in accordance with
Chapter 1, Section 1.2.
2.7.4
Lighting.
2.7.4.1
Black Light.
2.7.4.1.1
Characteristics.
Ultraviolet light is electromagnetic radiation with a wavelength ranging between X-rays and visible light. It is not
visible to the human eye. The ultraviolet range is usually divided into three bands: A) soft ultraviolet or long
wavelength (UV-A), 320 to 400 nm, which is commonly called black light; b) medium wavelength (UV-B), 270 to 320
nm, which is used for examining minerals and in suntan lamps; and c) hard ultraviolet or short wavelength (UV-C), 4
to 270 nm, which is used in germicidal or sterilizing lamps. Black light has the smallest band width of the ultraviolet
range and is just below visible wavelength range of 400 to 700 nm. Figure 2-26 is the electromagnetic spectrum
showing the relatively small band of black light used in fluorescent penetrant inspection. Black light is near the violet
end of the visible light range (near 400 nm).
Figure 2-26. Electromagnetic Spectrum Shows the Relatively Narrow Band of Black Light.
2.7.4.1.2
Interaction with Fluorescent Materials.
NOTE
Some optical plastics used in eyeglass lenses can fluoresce; causing a loss of eye
sensitivity when exposed to ultraviolet light. UV goggles should be worn over such
glasses to block the black light.
