LDT is a filename extension associated with ZEMAX software. LDT files store non-sequential photometry data. LDT files are typically used in laboratories, research institutes, and optical engineering companies.

In order to open LDT file, a ZEMAX installation, which requires a license key that can be purchased by contacting the software’s distributor, must be present in user’s system. ZEMAX is actively developed and the developer offers a comprehensive project documentation on its website.