Sorry for updating this after some time. I used EMS to report number of hours when daylight illuminance was between 100 and 2000 lux (i.e. useful daylight). A value of less than 100lux means it is too dark and a value of 2000 lux means it is too bright (can't remember the publication title but one of the authors was Christoph Reinhart of MIT).

bright. 
 
EnergyManagementSystem:Sensor,
 BlockIllumminance,      !- Name
 Block1:Zone1,                !- Output:Variable or Output:Meter Index Key Name
 Daylighting Reference Point 1 Illuminance;  !- Output:Variable or Output:Meter Name

Name
 
EnergyManagementSystem:ProgramCallingManager,
 Illu3,  !- Name
 EndOfZoneTimestepBeforeZoneReporting,  !- EnergyPlus Model Calling Point
 IlluProg3;     !- Program Name 1

1
 
EnergyManagementSystem:Program,
 IlluProg3,     !- Name
 IF (BedOcc2 > 0) && ((BlockIllumminance >2000)  || (BlockIllumminance <100)),
 SET ZoneIllu3 = ZoneTimeStep, 
 ELSE,
 SET ZoneIllu3 = 0,
ENDIF;

    ENDIF;
 
EnergyManagementSystem:GlobalVariable,
ZoneIllu3;

    ZoneIllu3;
 
EnergyManagementSystem:OutputVariable,
 Zone Illuminace Between 100 and 2000 Wile Occupied,  !- Name
 ZoneIllu3,         !- EMS Variable Name
 Summed,                  !- Type of Data in Variable
 ZoneTimestep;            !- Update Frequency