I believe there is a way utilizing the Io1 Io2 formula. There is another way utilized by Section XI IWA 2310 (I think it is) lower case letter card if you have the ability to reference an off code. Give me a little bit to dig and see what I come up with, both of those are from memory which isn't working to well after a night shift.

Regards,
Gerald

I just got a new one myself i sent the old out for calibration and they rejected it.
Then i needed to find some1 that is A2LA accredited to calibrate it.
i did get my purchaser to find a supplier that sent it to another facility for calibration, but now im thinking that i didnt put them on my supplier list ......
I dont think its a good idea to not have them on my list, nor is it a good idea to have the calibration date before the approval.

I've done some checking, and don't believe the calcs will do you any good.
The Closest thing your going to find is out of section XI.
IWA-2211 VT-1 Examination
(a) VT-1 examination is conducted to detect discontinuities
and imperfections on the surface of components,
including such conditions as cracks, wear, corrosion,
or erosion.
(b) The VT-1 examination procedure shall be demonstrated
capable of resolving characters in accordance
with Table IWA-2211-1.
(c) Direct visual examination distance requirements
shall be as specified in Table IWA-2211-1
........FC...........Max distance(ft/mm)..max height of characters inch/(mm)
VT-1 50...........2 (600).....................................................0.044 (1.0)
VT-3 50............ N/A........................................................0.105 (3.0)

NOTES:
(1) Resolution of the specified characters can be used in lieu of illumination measurement to verify illumination
adequacy.
(2) For procedure demonstration, a test chart or card containing text with some lowercase characters,
without an ascender or descender (e.g., a, c, e, o), that meet the specified height requirements is required.
Measurements of the test chart or card shall be made once before its initial use with an optical comparator
(10x or greater) or other suitable instrument to verify that the height of the lowercase characters
without an ascender or descender meets the specified requirements.

Thats probably as close as your going to get without a light meter, and pretty much only good for Section XI.

Then there is the visual criteria in Section V.
With some fancy wording and if a referencing code section calls out article 9, you could use the procedure qualification requirement of T921.2
and T921.3 in particular.
T-921.3 Demonstration. The procedure shall contain
or reference a report of what was used to demonstrate that
the examination procedure was adequate. In general, a
fine line 1⁄32 in. (0.8 mm) or less in width, an artificial
imperfection or a simulated condition, located on the surface
or a similar surface to that to be examined, may be
considered as a method for procedure demonstration. The
condition or artificial imperfection should be in the least
discernable location on the area surface to be examined to
validate the procedure.

Qual a procedure as per table T921 and go from there.

Take that with the requirements of T-952
T-952 Direct Visual Examination
Direct visual examination may usually be made when
access is sufficient to place the eye within 24 in. (600 mm)
of the surface to be examined and at an angle not less than
30 deg to the surface to be examined. Mirrors may be
used to improve the angle of vision, and aids such as
a magnifying lens may be used to assist examinations.
Illumination (natural or supplemental white light) for the
specific part, component, vessel, or section thereof being
examined is required. The minimum light intensity at the
examination surface/site shall be 100 footcandles
(1000 lux). The light source, technique used, and light
level verification is required to be demonstrated one time,
documented, and maintained on file.

It's a one time qualification.

Technically you could simply rent a calibrated light meter and write up a procedure
for lighting on a one time basis. Back that procedure up with either the lower case
letter card per Section XI IWA, and or the 1/32 grey line per T921.3.

Those are the only options I am aware of.

Regards,
Gerald

I agree with you, is this REALLY that important? no... tell him to work with you or you'll find a level III who will.