Dear Reader:

Facilities Managers won’t be surprised when learning there is sometimes a surprise around what he/she thought they were reading from a specification sheet, and what they see in terms of performance in their plant.

The science of lumens is susceptible to that, as manufacturers and Facilities Managers have no choice but to talk in two different languages.

A manufacturer expresses the performance of its fixture in terms of lumen output – the number of lumens of light emitted at the source, the surface or lens of the fixture. Once the lumens leave the fixture, obviously the manufacturer doesn’t control anything, including the height of the room, reflectivity of walls, process machinery locations that may cause shadowing, etc.

The Facilities Manager, however, is concerned with the amount of those lumens that actually reach the task area. By and large, what leaves the fixture is meaningle...