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A luminaire refers to a complete lighting unit - including one or more lamps, reflective surfaces, protective housings, electrical connections and circuitry. All these components affect the overall output of light from the unit, particularly the spatial distribution but also the amount. Even with a very powerful lamp, translucent or semitransparent materials may reduce the flow of light, reflective surfaces can quickly become dusty and dirty in some environments and also reduce output.

DIRECT

SEMI-DIRECT

DIRECT-INDIRECT

'DIRECT

SEMI-DIRECT

DIRECT-INDIRECT

The output distribution of a luminaire can be measured in the laboratory over a range of angles and plotted on a graph. This kind of graph is called a polar diagram as it is based on polar co-ordinates (an angle plus a scalar value). In it, the lines represent light levels actually measured at a fixed distance from the luminaire (usually 1m) as it was rotated around. For some geometrically complex lamps, their light output will not be symmetrical so more than one line must be used to represent output at different 'longitudinal' angles. In most cases the scalar units of this graph will be lumens, however (as shown below) these levels can be normalised from 0-1 to represent a multiplication factor to allow for the use of different lamp powers.

Figure 1 - Polar Diagram showing luminaire output at different angles from centre of beam.

Lighting manufacturers publish this data for each of their luminaires in the form of printed tables as well as IES data files. These are an ASCII format file that can contain any number of output values over any range of measurement angles, as well as basic information about the lamp(s) used and the overall dimensions of the unit.

Whilst products from different manufacturers will have their own unique output characteristics, there is still some basic commonality between the different types of luminaire. To assist designers select the most appropriate products for their particular application, the IES produce a range of example files for the most common luminaire types. The following table, whilst not an exhaustive list, shows a selection of these files.

It is quite important that a lighting designer have a reasonably clear understanding of the relationship between the shape and configuration of a luminaire and its resultant output distribution.

All the following distribution & polar diagrams where created using ECOTECT V4.

LUMINAIRE

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IES #1, PENDANT DIFFUSING SPHERE WITH INCANDESCENT LAMP

LAMP=INCANDESCENT