How to read a polar plot

Technical diagrams to inform your lighting choices

When working in the LED lighting industry, or even working with LED lighting products, a photometric polar plot will be encountered. These diagrams can seem confusing, or difficult to interpret, on the first view but they are relatively simple in reality.

These diagrams are useful to have on each product because it allows the person designing the lighting to choose the most appropriate lighting for the application. In offices, or schools, where the desks and workstations are known, a suitable luminaire can be specified to ensure adequate lighting for each area.

Collingwood ensures that photometric polar plots are shown on every product datasheet. We use the equipment in our laboratory to build the diagrams, so the results are as true a reflection of the product performance as is possible to have.

The first place to start is at the centre of the diagram, which is where the luminaire is mounted. The actual position of the luminaire can be different depending on the product type. An example of this would be an LED panel mounted on the ceiling, shining downwards, or a ground light mounted flush on the floor, shining upwards.

The diagram is then built up, from the centre point, with a series of concentric circles. Each of these circles relates to a different light intensity, measured in Candelas, with the scale also shown on the diagram. Much like the product position being different, depending on the application, so can the Candela scale – do make sure to review this each time.

On the Collingwood diagrams, there is a shaded area. This shaded area shows the lighting pattern for a particular product and how intense the lighting is at various angles, with the angles being labelled on the outside of the diagram. Typically, there will be a greater intensity of light where the products are directly pointed at, with the intensity dropping off as the angle increases away from the directional point.

Some particularly beneficial uses of photometric polar plots are for lighting designs on external applications. Landscape lighting has an obvious impact on nature and is a cause of light pollution in urban areas. Certain legislation around tolerances of up-spill of light for city centre areas and low level lighting for bats and nocturnal animals can be quickly cross referenced by looking at these diagrams.

Accordion Content