Pro Lite Technology

Luminaire Goniophotometry

Near-Field Goniometric Measurement 

Compact, near-field goniophotometer generates standard IES & EULUMDAT photometric files

So-called photometric data defines how much light a luminaire emits and into what directions. The measurement of luminaires has traditionally been performed with an illuminance meter placed in the photometric far-field which views the light source at one angle of azimuth and elevation at a time. The device under test is mounted on a motorised goniometer stage (the "goniometer") and the photometer views the lamp from a distance of between 10 and 25m, depending on the size of the light fitting. The cost of a typical far-field goniophotometer system (combined with the associated, large dark room) can be prohibitive, which has meant that most manufacturers have tended to call upon the services of independent test laboratories.

Now, a much more affordable and compact solution has been developed by Radiant Imaging which allows luminaire manufacturers to develop products and bring them to market more quickly and at lower cost. Pro-Lite was chosen to supply a Radiant Imaging NFMS near-field goniophotometer system by Designplan Ltd, a leading manufacturer of light fittings and luminaires. Designplan's Technical Manager, Lee McCarthy was able to justify his purchase based upon a 100% return-on-investment after testing approximately 40 luminaires, compared with the prices charged by an external test laboratory. 

Lee also points out that having access to an in-house photometric facility has meant that new product ideas and improvements can be tested "on the fly". This will allow him to bring new products to market more quickly and at reduced cost.

Polar Intensity Diagram

The goniometer system supplied comprised a motorised NFMS-0800 goniometer platform capable of handling luminaires up to 1.6m long, together with a ProMetric™ PM-1200N-1 CCD imaging photometer. The system operates under Radiant Imaging's FPMS-LI system software and records the angular luminance in the near-field. This is an important point to note: being a near-field system, the dark room necessary to accomodate the goniometer measured just 5 x 5m. The near-field luminance data is then scaled to far-field luminous intensity data through Radiant's ProSource software.

The far-field luminous intensity versus angle data for the device under test is then converted into an industry-standard format by the ProSource software, either IESNA (*.ies) or EULUMDAT (*.ldt). These standard photometric files also contain the light output ratio (LOR, a measure of the efficiency of the luminaire) as well as the integrated luminous flux and can be read by various lighting design programmes which lighting designers use to compute the number and power of light fittings required to illuminate a given area. 

Pro-Lite gratefully acknowledges the permission of Designplan to publish this article. For further information on the Radiant Imaging NFMS goniometer, click here. To learn more about other products that we offer for those working with lamps & luminaires, click here.

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