Friday, March 22, 2013

Inconsistent gamma values in EULUMDAT (and IES) files.

When we look at the definition of a C-gamma distribution, we can conclude that gamma angle 0° for each C-plane points in the same direction: straight down. Similarly the gamma angle 180° points straight up, for every C-plane. Consequently it should be considered an ERROR in the file when the luminous intensity values for these coincident angles in either cd/klm, candelas, or footcandles are different! Yet there are many files that have this error! What would be the value you use to calculate glare in that direction, or the illuminance? I think these problems result from the measurement protocols, where the anomalies of temperature variation or impact of orientation during measurement is not properly post-processed. In the next release of EulumdatTools these errors are caught, so that they can be manually corrected.