Lighting Measurements

The main units of measurement for light are the Lumen and Lux.

Lumen
This is a measurement of the light output from a lamp.
Water Analogy: the amount of water spraying from a shower head.

Lux
This is a measurement of the light intensity falling on a surface. One lux is equal to one lumen per square metre. The Australian standard AS1680 gives lux levels for many different industries.

In order to calculate the lux level on a surface we need to consider the following:

	Room Dimensions
	Luminaire Mounting Height
	Height of the Work Plane (desk, workbench or floor)
	Reflectances of the Ceiling, Walls and Floor
	How Dirty will the Room Surfaces and the Luminaire become in Several Years Time
	Photometric Data on the Fitting to be Used
	Initial Lumen Output of Each Lamp x the Number of Lamps
	What will the Lamp Lumen Output be in Several Years Time

These parameters are usually processed in a computer program which will tell us how many fittings are required for the space. The result will be the "maintenance illuminance" which tells us that the light level will be in Lux after several years of operation. This means that if we measure the illuminance of a new installation the Lux level should be considerably higher than the Lux we designed for.