What a photometric file is for
LM-63 defines the electronic transfer format for photometric data and related information. A file supports calculations; it is not itself evidence that the installed product matches the represented test sample. Match the luminaire configuration and report identification before using it. [1]
Ask for the complete test boundary
LM-79 addresses optical and electrical measurements of solid-state lighting products. Request the report for the exact optics, output setting and electrical configuration being specified. Record the sample and laboratory conditions instead of combining unrelated headline values from multiple configurations. [2]
A directional distribution tells a different story
Intensity is flux per solid angle in a direction. Two products can have equal lumens and very different beams. A narrow distribution can concentrate light while leaving adjacent areas relatively dark; a wider one can redistribute the same output. Distribution and aiming belong in the calculation. [3]
The inverse-square teaching model
For a sufficiently small source in the far field, illuminance on a plane normal to the ray is I divided by distance squared. With 400 cd at 2 m, the idealized result is 100 lx; at 4 m it is 25 lx. An oblique plane adds a cosine factor. This simple model excludes room interreflection and extended-source effects.
Model, inspect, then measure
Our workflow checks fixture position, orientation, calculation grids, surface assumptions and output settings before comparing results. After installation, compare measurements under a documented operating state. A difference can come from geometry, settings, maintenance or measurement procedure, not only from a defective product.