Consider VFR minima
VFR by day or night: Not above 3 Octas of cloud within 5 nm radius
Special VFR: 1.5km visibility, cloud ceiling 600ft, 2 way radio communication, must be in CTR [may not be planned]
ATZ, ATZ, CTR: 5km visibility, 2,000ft horizontal, 500ft vertical
1,000ft AGL & FL100: 5km visibility, 2,000ft horizontal, 500ft vertical
FL100 to FL195: 8km visibility, 1,5km horizontal, 1,000ft vertical
If none of these fulfill the scenario, then that particular portion of flight should be logged as flight conducted under Instrument Meteorological Condition.
If it is a training flight and the pilot flies solely by reference to instrument, then that particular time during which the pilot flies solely by reference to instrument would be logged as flight conducted under Instrument Meteorological Condition.
No Flight above FL195 would be considered Visual Flight. The time spent above FL195 should be logged as instrument flight time.