A lux meter measures illuminance at the sensor position and plane.
A lux meter is a measuring instrument for illuminance. The reading is useful only when the plane, position and operating condition are recorded.
Technical meaning
A lux meter reads illuminance at its sensor, normally expressed in lux.
The reading can change with sensor angle, height, location, nearby shadows, daylight, fitting output and surface reflectance.
Lux meter point gridPoint labels keep the average, low point and spread tied to the same measured plane.
Calculation use
Lux meter readings can check whether a simple estimate is in the right range for the assessed plane.
Indoor and outdoor readings can be paired for a daylight-factor calculation when taken under the same daylight condition.
Not the same as
A lux meter is not a complete lighting design tool by itself.
One reading does not prove uniformity, glare control, maintained performance or suitability for every task in the room.
Australian context
Australian lighting notes should state the meter location, assessed plane and operating condition before a reading is compared with a room or workplace target.
Examples
Example
Value
Planning note
Bench measurement
sensor on workplane
The reading belongs to the bench, not the whole kitchen.
Office desk grid
several desk points
Multiple points reveal variation that an average estimate can hide.
Daylight pair
indoor and outdoor lux
The pair can support a daylight-factor calculation.
Lux meter readings are measurement notes. Project decisions still need suitable measurement practice, task definition and the relevant reference pathway.