Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
@BORM 's answer is largely accurate, but I would add:
The proper height of an illuminance map should correspond to best practice or be as dictated by metrics. North Amercian best practice for calculating horizontal illuminance in interior spaces, as well as IESNA LM-83 (standard for calculating spatial daylight autonomy) both dictate 30" (0.762m) above the finished floor for this. Not coincidentally, the Sketchup plugin will try to automatically place illuminance map objects at this height in your model (unless Sketchup tries to snap to a corner or something).
You must associate your daylighting controls with the illuminance maps in order for the Radiance Measure to function properly.
You don't HAVE to use Radiance to calculate these illuminance maps, you can also use EnergyPlus' internal daylighting engine. If you choose to just (and I do mean just) use EnergyPlus' daylighting engine, you don't even have to associate the maps and the controls. Just put the objects in the model and you'll get illuminance maps in the energyplus output. For what it's worth.
Both of these methods will only show you spatial daylight illuminance distributions for rectangular areas and on a thermal zone by thermal zone basis. If you wish to see the daylighting across the entire building, perhaps floor by floor, you will need to get creative and take the numeric/merged_space.map and output/merged_space.ill files and map the spatial data in the .map file to the (hourly-indexed) illuninance data in the .ill file. This is an exercise for the community at large. =)
