How to read a photometric file

A photometric file is a contract between the manufacturer and the lighting designer: it describes, in a machine-readable format, exactly how a luminaire distributes light.

The three numbers that matter most are the luminous flux, the intensity distribution curve and the utilisation factor in the intended application. Check them at your actual mounting height — a curve that looks beautiful at 3 metres can collapse at 6.

Finally, verify the file against the printed datasheet. Small discrepancies are normal between revisions; large ones are a reason to ask the manufacturer directly.