Standard Practice for Measurement of Emission Characteristics and Requirements for LED UV-A Lamps Used in Fluorescent Penetrant and Magnetic Particle Testing

Abstract

4.1 UV-A lamps are used in fluorescent penetrant and magnetic particle examination processes to excite fluorophores (dyes or pigments) to maximize the contrast and detection of discontinuities. The fluorescent dyes/pigments absorb energy from the UV-A radiation and re-emit visible light when reverting to its ground state. This excitation energy conversion allows fluorescence to be observed by the human eye. 4.2 The emitted spectra of UV-A lamps can greatly affect the efficiency of dye/pigment fluorescent excitation. 4.3 Some high-intensity UV-A lamps can produce irradiance greater than 10 000 μW/cm2 at 15 in. (381 mm). All high-intensity UV-A light sources can cause fluorescent dye fade and increase exposure of the inspector’s unprotected eyes and skin to high levels of damaging radiation. 4.4 UV-A lamps can emit unwanted visible light and harmful UV radiation if not properly filtered. Visible light contamination above 400 nm can interfere with the inspection process and must be controlled to minimize reflected glare and maximize the contrast of the indication. UV-B and UV-C contamination must also be eliminated to prevent exposure to harmful radiation. 4.5 Pulse Width Modulation (PWM) and Pulse Firing (PF) of UV-A LED circuits are not permitted. Note 1: The ability of existing UV-A radiometers and spectroradiometers to accurately measure the irradiance of pulse width modulated or pulsed fired LEDs and the effect of pulsed firing on indication detectability is not well understood.