Vertical Footcandles: How High the Measurement

There has been some conversation here about the concept of vertical footcandles. Across the industry, this seems to be an issue that is not very well understood. Vertical footcandles are a measure of light intensity at the site boundary across a vertical plane. So if horizontal footcandles what you get if you take a light meter and hold it parallel to the ground, Vertical footcandles is the reading you would get if you hold the light meter perpendicular to the ground (parallel to the light poles and the building walls). If you are standing erect and looking into the site from the site boundary, your eyes are detecting primarily vertical footcandles. I'll post a drawing to illustrate what I'm talking about. The next question is: how high off the ground should you take your measurements? Unfortunately, LEED is silent on this point. In talking to Dane Sanders at Clanton Associates, he confirmed that there is not much guidance here, but that they have been using ground level and have had several projects successfully earn this credit. Dane also shared a sample site photometric plan for vertical footcandles for the Hannaford supermarket that just earned Platinum. I've posted that to the Documentation Toolkit. Hope that helps.