Lumens, lux, candela, and light efficiency are four completely different measurements; confusing them is the most common reason why a buyer finally gets a lighting system that "does not meet expectations." The parameter list does not remind you, it defaults to you that you already know the difference.

Lumen is the total luminous flux emitted by the light source in all directions, and it doesn't tell you at all where the light has gone. Lux is the illuminance-the number of lumens falling on each square meter of surface-that depends entirely on distance and light distribution. Candela is the intensity of light in a specific direction, and the light distribution curve plots it. Light efficiency is measured in lm/W, which is the ratio of output to power consumption, and is also the number that determines operating costs.

This is why the term "equivalent wattage" requires vigilance. There is no standard definition of how many watts of LEDs a 150W incandescent lamp is "equivalent" to. Manufacturers can completely use their best beam to compare their opponents 'worst beam. When the same lamp widens the beam, the illuminance on the target surface drops, but the lumen count remains unchanged.

For a credible lumen count, ask which test standard it comes from. LM-79 is a recognized method for measuring integrated LED luminaires; if a life statement is also given, LM-80 data covering the LED device and TM-21 extrapolation results should also be provided. The dealer only reports an isolated lumen count and no test source. That is the design goal, not the measurement value.