Light measurement

The luminaire’s light distribution is measured on several C-planes around the luminaire, at intervals of at least 15°. First measurement plane (C=0°) is across the lamps’ longitudinal axis. γ-angles – several angles are measured, at least every 5 degrees (see figure).

Light distribution curve

The light distribution curve drawn in a polar diagram denotes the luminaire’s luminous intensity in different directions as a function of viewing angle in one or more planes. It is usually represented by an unbroken line that indicates the light distribution perpendicular to the light source’s longitudinal axis and with a dashed line that indicates the light distribution in direction of the longitudinal axis.

The values of the light distribution curves are scaled to correspond to 1000 lm from the light source (cd/1000 lm, cd/ klm). This is why it is often possible to show luminaires with different outputs on a common polar diagram.

Normalized luminous intensity
Normalised luminous intensity data of a luminaire (equipped with a lamp or lamps of specified type and power) shall be given as a table, normalized to a luminous flux of 1,000lm and provided in candela per kilolumen (cd • klm ^-1).

530cd/klm in 0 degrees

The diagram shows, using curves (or scales) a predefined area, inside which the horizontal illuminance exceeds the curve’s lux value. The position of the luminaire is usually indicated on the diagram. Alternatively, the isolux diagram can be represented by a 3D diagram, which is best suited for showing the uniformity of the lighting installation.

The calculation points’ illuminance values can be introduced onto the premises’ layout drawing and the results given in table form. The results are available in all the above mentioned forms in DIALux.