Light fixture, or luminaire, data file used by DIALux, a professional light planning software for indoor and outdoor lighting; stores lighting parameters for a luminaire, which include the number of lamps, the light intensity, the light distribution curve, and the size of the luminaire.

LDT files are saved in plain text using DIALux's Eulumdat format. They can be edited with the free LDT Editor program, which was developed by DIAL. DIALux is a free software application used to design and plan lighting installations for homes, office buildings, neighborhoods, commercial sites, and other environments.