The ISO published ISO 13655:2009 which specifies different measurement modes to be used to accommodate the way different papers have differing levels of optical brightening agents (OBA's). Most measuring instruments developed since 2009 have identified which modes are being used when measuring.
M0 “Color measuring mode A”
Spectral luminance factor without polarization filter under a light source that simulates standard illuminant A. This typically includes some UV light.
M1 “Color measuring mode D50”
Spectral luminance factor without polarization filter under a light source that simulates standard illuminant D50 with correct UV component. This mode measures with an illuminant that simulates daylight, including all the UV light of daylight.
M2 “Color measuring mode UV Cut”
Spectral luminance factor without polarization filter under a light source that simulates any standard illuminant without UV component. This mode measures while cutting out any UV light in the measurement.
M3 “Measurement with polarization filter”
M3 has the same sample illumination requirements as M2 and includes a linear polarizer. This mode measures while cutting UV light and utilizing a polarization filter.