LED Black Light Intensity Limitiations

James Scalf
NDT Inspector, Global Integrity, Canada, Joined Oct ,
277
James Scalf
NDT Inspector,
Global Integrity,
Canada,
Joined Oct
277

NDT Inspector,Global Integrity,Canada,Joined Oct

Link to AJR

13:34 Oct-01-

https://www.ndt.net/forum/thread.php?msgID=#

LED Black Light Intensity Limitiations 13:34 Oct-01-

Good Day My Friends and Peers,

I am in search of some information, if it exists. I am wondering if there are any code or standards limiting the upper end of Black Light Intensities for LED Style (battery of hard lined) UV-A Lamps?

As we know LED UV-A Lamps can be quite intense so much so that to have lamps that exceed 10,000 micro-Watts per Centimeter Squared in intensity is common (We even have a few in the RCAF inventory that exceed 19,999.99 micro-Watts per Centimeter Squared which exceeds the upper limit of our UV-A meters). Lamps of this strength can and do, as ASTM E--18 explains, cause a wash out of the fluorescence thus decreasing the sensitivity of the agent being used for the inspection (be that LPI or MPI).

I know ChiNDT and Labino are now producing Lamps that are limited in intensity and they cite ASTM E-, Rolls Royce RRES and Airbus AITM6- as the standards to which they were developed to meet. Further that they have intensities of 4,000 micro-Watts per Centimeter Squared (for the Labino MB Hercules EX) as an example. For the ChiNDT Lamp it is below 6,000 micro-Watts per Centimeter Squared. I have the ASTM E -18 but it doesn't provide much guidance for my inquiry and I cannot source the other two Documents. I have asked both the distributors of the ChiNDT and Labino Lamps, I deal with, to see if they cannot get me copies but that was over 6 months ago now and still no response.

What I am seeking is a formal document from one of the national councils, such as Transport Canada, European Flight Authorities or the US FAA, which direct that Black Light Intensities for the purposes of conducting inspections on aerospace components, using Fluorescent Penetrant or Fluorescent Magnetic Particles, shall be limited to a minimum intensity of 1,000 micro-Watts per Centimeter Squared and a maximum intensity of 7,000 micro-Watts per Centimeter Squared.

I had heard talk at one of the conferences that there was talk about limiting the upper end of the intensity to between 7,000 and 7,500 micro-Watts per Centimeter Squared but have not come across any formal documents as yet and was hoping maybe one of you in the community might be aware of any relevant documents.

Thanks for your time and attention on this matter. Hopefully someone will have the information. Cheers...

Sincerely,
James

Eddy Rosales
NDT Inspector,
Canada,
Joined Jan
25

NDT Inspector,Canada,Joined Jan

19:12 Oct-01-

https://www.ndt.net/forum/thread.php?msgID=#

Re: LED Black Light Intensity Limitiations 19:12 Oct-01-In Reply to James Scalf at 13:34 Oct-01- (Opening).

Hi James,

I think you should check out ASTM E
standard guide for use of UV-A and Visible light sources and meters used in liquid penetrant and magnetic particle methods.

I have an older copy if you want to look through it . I will attach some information that might be useful from that standard.

Significance and Use
5.1 UV-A and Visible light sources are used to provide
adequate light levels for liquid penetrant and magnetic particle
examination. Light meters are used to verify that specified light
levels are available.
5.2 Fluorescence is produced by irradiating the fluorescent
dyes/pigments with UV-A radiation. The fluorescent dyes/
pigments absorb the energy from the UV-A radiation and
re-emit light energy in the visible spectrum. This energy
transfer allows fluorescence to be observed by the human eye.
5.3 High Intensity UV-A light sources produce light intensity
greater than 10,000 μW/cm2 at 38.1 cm [15 in.].

6.1.2 The UV-A range (used for fluorescent liquid penetrant
and fluorescent magnetic particle examinations) is considered
to be between 320 nm [ Å] and 400 nm [ Å]. The
UV-B range (medium UV) is considered to be between 280 nm
[ Å] and 320 nm [ Å]. The UV-C range (short UV) is
considered to be between 180 nm [ Å] and 280 nm [
Å]. The visible spectrum is considered to be between 400 nm
[ Å] and 760 nm [ Å].
6.2 Mercury Vapor UV-A Sources
6.2.1 Most UV-A sources used in fluorescent NDT utilize a
lamp containing a mercury-gas plasma that emits radiation
specific to the mercury atomic transition spectrum. There are
several discrete lines of the mercury spectrum in the ultraviolet
section of the electromagnetic spectrum (between 180 nm
[ Å] and 400 nm [ Å]). The irradiance output is
dependent on the gas pressure and the amount of mercury
content. Higher values of gas pressure and mercury content
result in significant increase in its UV emission.
6.2.2 UV-A sources used for NDT, employ appropriate
filters, either internal or external to the light source to minimize
the visible light output (400 nm [ Å] to 760 nm [ Å])
that is detrimental to the fluorescent inspection process. These
filters should also block harmful radiation below 320 nm [
Å].
6.2.3 UV-A sources are generally low or medium pressure
vapor sources. Low pressure lamps are coated with a special
phosphor in order to maximize the UV-A output. Medium
pressure lamps do not have phosphor coatings but operate at
higher electrical power levels, resulting in significantly higher
UV-A output.
6.2.4 Typically, low pressure lamps (tubes) are used in wash
stations or for general UV-A lighting in the inspection room.
Medium pressure lamps are used in fluorescent inspection
stations. A well designed medium pressure UV-A lamp should
emit less that 0.25 % to 1 % of its total intensity under 320 nm
[ Å] and above 400 nm [ Å]. A UV-A bulb based on
the American National Standards Institute&#;s Specification H 44
GS-R100 is a 100 watt mercury-vapor bulb in the Par 38
configuration and normally using a Kopp UV filter.
Other newer lamps using the same bulb but with the Kopp
UV filter or bulbs based on the Philips HPW 125-watt
bulb4 will not differ greatly in UV-A output, but in general will
produce more visible light in the blue/violet part of the
spectrum. Warning&#;Certain high-intensity UV-A light
sources may emit unacceptable amounts of visible light, which
will cause fluorescent indications to disappear. Care should be
taken to use only bulbs certified by the supplier to be suitable
for such examination purposes.

Eddy Rosales
NDT Inspector,
Canada,
Joined Jan
25

NDT Inspector,Canada,Joined Jan

19:52 Oct-01-

https://www.ndt.net/forum/thread.php?msgID=#

Re: LED Black Light Intensity Limitiations 19:52 Oct-01-In Reply to Eddy Rosales at 19:12 Oct-01- .

Hi James,

to add to my first reply,

I dont believe you will find any documents that tell you a max.
I would say that as long as you have a min of 1,000 micro-Watts per Centimeter Squared and no more than 2ft (white light) you should be fine.

All I have found on documents when it comes to high intensity UV-A lights is that they "may" put out to much white light that can wash out / decrease the sensitivity. I would use a white light meter and be sure to not exceed 2ft .

I hope this helps

Rick Lopez
R & D, John Deere - Tech Works Ames, USA, Joined Jul ,
217
Rick Lopez
R & D,
John Deere - Tech Works Ames,
USA,
Joined Jul
217

R & D,John Deere - Tech Works Ames,USA,Joined Jul

21:48 Oct-02-

https://www.ndt.net/forum/thread.php?msgID=#

Re: LED Black Light Intensity Limitiations 21:48 Oct-02-In Reply to James Scalf at 13:34 Oct-01- (Opening).

Hello James,
I am not aware of any code requirements or similar from national councils, but some aerospace OEM standards did migrate some number of years ago to a maximum UV-A irradiance because of the possibility for fluorescent penetrant photobleaching. I have never seen evidence of fluorescent MT particles photobleaching, but never explored that avenue as deeply (pigments in MT are encapsulated and thus avoid air exposure while in the excited state, while PT dyes are open to the air). That said, it is likely easier for an MRO shop to maintain UV-A sources following a single irradiance guideline (i.e. max of 5,000 uW/cm^2), rather than trying to track which method a source is used for.

Regarding the Rolls standard (RRES ), a copy that I have access to does mention the uW/cm^2 limit in Sections 8.3, 8.4, and 9.2.

Eddy, I would not recommend using a visible light photometric sensor for evaluating the amount of visible light emitted by a UV-A source, as accuracy will be extremely bad. Many standards incorporate this guidance by specifying how visible light illuminance is measured. Lighting condition, or evaluation of leaked visible light (e.g. from a ripped or inadequate black-out curtain around the inspection booth) use this type of meter. ISO , for example, specifies: "The reading from the illuminance meter shall not be affected by UV-A irradiance." There really isn't a shop-floor test for measuring visible light emitted by a UV-A source (e.g. spectrophotometer coupled to an integrating sphere).

Regards

Eddy Rosales
NDT Inspector,
Canada,
Joined Jan
25

NDT Inspector,Canada,Joined Jan

22:52 Oct-02-

https://www.ndt.net/forum/thread.php?msgID=#

Re: LED Black Light Intensity Limitiations 22:52 Oct-02-In Reply to Rick Lopez at 21:48 Oct-02- .

Hi Rick,

Thank you for your input on my suggestion, I would like to point out that I do know what a light meter is used for, thank you for that.

since there is nothing that really tells you dont use more than xxxxxx micro-Watts per Centimeter Squared as a general rule, I simply suggested that as long as you comply with the minimum that is 1,000 and no more than 2ft you should be fine, unless you have a standard that tells you other wise.

you can always do your own test with the TAM panels and test parts and compare results with two UV lights.

particles or penetrant are excited by a UV light at a specific light wave length, Spectroline makes UV lights that have an intensity as high as 50,000 micro-Watts per Centimeter Squared. I wouldn't rule these out and say because they do more than 5,000 they are no good.

Contact Spectroline and ask them about their MIL-S light and ask about the risk of 50,000 doing the washout.

http://spectroline.com/product/ml--series-forensics/

If you want to learn more, please visit our website Ndt Uv LED Lamp.

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Peter P.
Consultant, ASNT MT/PT Level 3, Quality Manager SharingNDT, USA, Joined Jan ,
81
Peter P.
Consultant, ASNT MT/PT Level 3, Quality Manager
SharingNDT,
USA,
Joined Jan
81

Consultant, ASNT MT/PT Level 3, Quality ManagerSharingNDT,USA,Joined Jan

23:30 Oct-02-

https://www.ndt.net/forum/thread.php?msgID=#

Re: LED Black Light Intensity Limitiations 23:30 Oct-02-In Reply to James Scalf at 13:34 Oct-01- (Opening).

Hey James,

Nothing definitive is any ASTM, AMS, FAA, etc standard, only prime requirements. Something I just discovered that I've never heard come up before is the minimum requirement at the maximum distance, in this case µW/cm², interesting.

According to RRES (Appendix C): the intensity at peak maximum shall be μW/cm² for the minimum working distance and μW/cm² for the maximum working distance.

I know the owner from Labino pretty well, do you need a copy of Rolls and Airbus requirements?

James Scalf
NDT Inspector, Global Integrity, Canada, Joined Oct ,
277
James Scalf
NDT Inspector,
Global Integrity,
Canada,
Joined Oct
277

NDT Inspector,Global Integrity,Canada,Joined Oct

14:14 Oct-03-

https://www.ndt.net/forum/thread.php?msgID=#

Re: LED Black Light Intensity Limitiations 14:14 Oct-03-In Reply to Peter P. at 23:30 Oct-02- .

ET AL,

I appreciate the feedback. I would appreciate having a copy of the Rolls Royce Standard as long as we are not infringing on what may be proprietary information. I do not wish for any of you or myself getting into trouble for the sake of research.

For a little background on why I am researching this. we (the RCAF) have had in the last few years a few minor indications missed by technicians in the field. I have inquired of the technicians involved and they have walked my through the procedure they conducted (LPI) and they did nothing wrong as far as I can tell. The only commonality was the Manufacturer, Brand, and Type of LED Black light. so I suspect it may have been these that were the cause of the indications being missed. Fortunately there has not been a catastrophic result as yet but I am trying to see if there is any supporting documentation that can be sourced relating to limiting the upper end of the intensity for the UV-A LED Lamps.

It may come down to our Airworthiness Authority simply decreeing an arbitrary upper limit but I would prefer if I could cite an actual source document.

Again thanks everyone for the information. Rick and/or Peter I would like the chance to read the Rolls Royce RRES specification if you are allowed to share it.

Have a great day everyone,
James

 

Is my mercury vapor light in compliance with ASTM E-18? No. ASTM E-18 is only applicable for UV-A LED lights. It is not applicable for mercury vapor, gas-discharge, arc or luminescent (&#;uorescent) lamps or light guides (for example, borescope light sources).

Is my mercury vapor light in conjunction with an LED replacement bulb in compliance with ASTM E-18? No. It is the responsibility of the manufacturer to certify a specific UV LED lamp as a single unit, taking into consideration ALL the parts that make up the light such as the housing, &#;lter, diodes, electronic circuit design, optical elements, cooling system, and power supply combination. When you buy one of the above components, in this case the diodes, there is no guarantee that use of the diodes with any mercury unit will not shift the wavelength of the diodes outside the 360-370nm region. Nobody tested the body with the diodes and therefore nobody can claim compliance with ASTM E-18.

If my certificate says E-15, should I ask for a certificate which says E-18? No. There is no need. The difference between E-15 and E-18 is just a conversion factor that was corrected. Nothing fundamental has changed in E-18 that should be part of your certificate.

I have lost my ASTM E-18 certificate, can I get a copy? Although the standard does not refer to storage of data, all major manufacturers store the data to reproduce your certificate. Labino does that for free.

Can I repair my UV light on my own? It depends what is broken. If it is something unrelated to the optical output such replacing the PSU or an external cable, so long as you are qualified and/or authorized by your company, you can repair it. However, the burden and most often the knowledge, of making a light perform in accordance with ASTM E-18 lies with the manufacturer (Sect. 1.2). A certification is an action that requires several hours to complete, requires specialized equipment (for example a spectrometer) and an excellent interpretation of the standard. Repairs relating to the optical performance of the light must be left to the manufacturer or an authorized service center.

When does my UV LED light needs re-certification? A light should be re-certified by the manufacturer or an authorized service center of the manufacturer only. The re-certification is required only if a critical component that affects the performance of the light is damaged. Such components are typically components that are inside the housing such as a failing LED, a burned drive card etc. No re-certification is needed if you need to replace components external to your light such as your power supply unit, a power cord, or batteries.

What is the difference between a Type Test and a Unit Test report? A Type Test report is a very detailed and comprehensive report that each manufacturer makes on a specific model using a reference light (not the light sold to you) within that model. The reference light is stored safely and should be made available in case of an audit. A Type Test report should be made available to users upon request. A unit test report records tests that are made on the light that users have purchased. A unit test report should be included with your light.

Who regulates implementation of the ASTM E-18 standard? Nobody. ASTM E-18 tests and measurements are made by the manufacturers for their own products. It is therefore necessary to choose a credible manufacturer before you make an investment. Specific sections of the standard are audited by Nadcap and/or ISO auditors. ASTM E-18 is referenced and adopted by all major NDT procedures such as ASTM E (Standard Practice for Magnetic Particle Testing) and ASTM E (Standard Practice for Liquid Penetrant Testing).

What do I do if I operate a light with several UV LEDs bundled together in the same position and I cannot see if any have failed? ASTM E-18 does not comment on how LEDs should be positioned or how many they should be, so long as all the acceptance tests are met. However, one drawback with UV LEDs positioned together is that you cannot see if any failed, especially since there is a filter covering them. You will only know if you measure the UV output and detect a sharp drop in intensity. Testing equipment should be controlled, and failures detected.

My company has two different digital UV-A meters that show different readings each. Why? Check if your units have been recently calibrated from an ISO calibration lab or equivalent, with Scope of UV and White Light measurements. An ISO calibration lab is not qualified to calibrate everything. Check if the UV sensor diameter is greater than 0.5 inches (12.7 mm). This might explain the extra error. The UV sensor diameter should not be greater than 0.5 inches (12.7 mm). Both requirements are part of the ASTM E-18, Section 6.1: &#;Ultraviolet radiometers shall be calibrated in accordance with ANSI/ISO/IEC , ANSI/NCSL Z540.3, or equivalent. Radiometers shall be digital and provide a resolution of at least 5 µW/cm2. The sensor front end aperture width or diameter shall not be greater than 0.5 in. (12.7 mm).&#;

Why do my old analog meters not measure the same for a UV-A LED light versus a Mercury UV-A light? The answer is simple. Mercury UV-A lights emit a lot of light in wavelengths away from 365 nm and many old meter models were not designed to handle large concentration of light around a specific wavelength. UV LED lights emit a lot of light around 365 nm. Irradiance coming out of a UV LED lamp is best measured with a digital meter. Digital UV radiometers for NDT are made with a filter and a detector. The detector is measuring ALL the light that gets transmitted through the filter, typically around the 365nm area.

Are there any safety concerns from the use of UV-A LED lights? UV lights can be harmful to the eyes and skin and protection should be proportionate to the associated risk, as NOT all UV lights are the same. Injuries and blindness can be the result of exposure to ultraviolet (UV). Lights sold in Canada, the European Union and some Asian countries are required to be tested to the IEC standard. The equivalent standard in the United States is ANSI/IESNA RP-27. These two standards are similar in context and provide guidance for evaluating the photobiological safety of lamps. Specifically, they define exposure limits, reference measurement techniques and the classification scheme for the evaluation and control of photobiological hazards from sources of optical radiation, including LEDs, in the wavelength range from 200 nm through nm. Any UV LED manufacturer that claims the CE mark should have these tests taken.

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