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Pioneering LED Illumination
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PostPosted: June 21st, 2012, 5:37 pm 
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For NDT, Lights are used for Penetrant Inspection (PI) and Magnetic particle inspection (MPI).

Light sources comparison:
HID:
1. Consumes high power
2. Operates at high temperature, 150 degree at body, 230 degree at filter
3. Weigh over 6 pounds with ballast, or over 2 pounds for just lamp
4. AC powered, or with large battery
5. Magnetic fields may make the light shut off, then it requires 10-15 minutes to cool-off and 10-15 minutes to warm up again, or affect discharge and therefore slightly vary the light output
6. Mercury-based product
7. Cracked filter will increase the emitting of white light and harmful UV light.
8. Lifetime 5000-12000
9. Micro discharge lamp (MDL) will be instant on/off
LED:
1. Consumes low power
2. Operates at lower temperature, 40-50 degree at housing, 70 degree at LED head.
3. Light weight,
4. DC powered, or with small batteries
5. Instant on/off to full power
6. Mercury free
7. Light wavelengths are typically 365(+-5)nm with half bandwidth of 15nm, safer
8. Lifetime 30000-50000 hours,
9. Easily be configured into a variety of new designs, utilizing multiple LEDs.
10. Easily be dispersed or focused to get better beam uniformity

UV 365nm LED light improvements:
1. Intensity management: what is optimal for some users might be too intense for others.
Current for the UV 365nm light can be regulated and varied.
2. White light management: a good quality UV 365nm LED light have extremely high UV and produce highly concentrated beams. This can often lead to high visible light readings due to naturally fluorescing materials that may present on meter sensor.
A UV pass filter can be used to attenuate some UV intensity and to reduce visible light.


Penetrant Inspection (PI)
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PI.png
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• Fluorescent penetrant offers an advantage over a visible for finding very small defects.

Magnetic particle inspection (MPI)
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MPI.png
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• Wet magnetic particle (in water or oil) can be visible or fluorescent.
• Wet magnetic particle method is more sensitive than the dry because the suspension provides the particles with more mobility; It uses smaller particles and make it easy to apply the particles uniformly to a relatively large area.
• Oil-based carrier offer superior corrosion and hydrogen embrittlement protection to materials

Light requirement for Visible Penetrant and Visible Magnetic Particle:
1. Artificial lighting is recommended to improve uniformity in lighting between inspections
2. The artificial lighting used for visible penetrant is usually white flood light.
3. The light intensity: 100 foot-candles is required at the surface being inspected, too much light may cause excessive reflected light that could distract from the inspection, many specifications do not require the white light intensity check to be conducted at a specific distance

Light requirement for Fluorescent Penetrant and Fluorescent Magnetic Particle:
1. The desired wavelength range for use in nondestructive testing is between 350nm and 380nm with a peak wavelength at about 365nm.
2. The fluorescence is at 520-580nm. Fluorescent brightness is linear to ultraviolet intensity.
3. Intensity or distance change will have direct impact on the inspection.
4. Normally accepted intensity is 1000 mW/cm2 @ 15 inches.
5. White light levels of less than 2 fc are required by most procedures, some may require less than 0.5 fc white light at the inspection surface. Procedures require a check and documentation of ambient white light in the inspection area


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