PM-NFMS Near-Field Goniophotometer for Luminaires

The PM-NFMS from Radiant Imaging combines a motorised goniometer stage with a ProMetric CCD imaging photometer to perform a near-field angular analysis of the luminance and colour from LEDs, luminaires and solid state lighting. ProSource software then scales this to far-field luminous intensity data from which standard photometric files are generated (IESNA, EULUMDAT). So-called photometric data defines how much light a luminaire emits and into what directions; lighting designers then use this standardised data format with a variety of commercially-available lighting design programmes to determine the number and positioning of luminaires in order to create the desired illuminance (lux level).

The Near-Field Difference

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, the actual working distance depending on the size of the light fitting. The cost of a typical far-field goniophotometer system (combined with the associated, large dark room) was often prohibitive, which meant that most manufacturers have used the services of independent test laboratories. The PM-NFMS goniophotometer changes all this by exploiting the latest advances in imaging photometry to make luminaire measurements more accessible and affordable.

Rather than using an illuminance meter in the photometric far-field to record the illuminance as a function of angle, the PM-NFMS employs a ProMetric CCD imaging photometer to record spatially-resolved images of the near-field luminance emitted from the light source. Luminance (units of cd/m²) is the optical property one measures when working up close to the light source. Spatially-resolved images of the source luminance are recorded in Radiant Imaging's proprietary ProSource (.rs8) format for one angle of azimuth and elevation at a time. The associated, motorised goniometer stage scans the device under test over ± 88° in all directions. Radiant Imaging's ProSource software then performs a ray-tracing operation to scale the near-field luminance readings to equivalent far-field illuminance values at the click of a mouse. Standard photometric files in the IESNA (.ies) and EULUMDAT (.ltd) format can then be generated. The photometric data reported also includes the light output ratio (LOR, a measure of the efficiency of the luminaire) as well as the integrated luminous flux (units of lumens).

Return on Investment Measured in Months

The benefits of near-field goniophotometry are numerous:

• Being a near-field measurement, the dark room required is much smaller than for a traditional far-field installation. The room size depends upon a number of factors but plan on a laboratory meaasuring no more than 5 x 5m. This greatly reduces the facilities cost necessary to perform luminaire measurements.
• The cost of the near-field goniophotometer system hardware is also a fraction of the price of a traditional far-field installtion. The PM-NFMS can pay for itself compared with the costs associated with having samples tested independently after a few tens of measurements.
• Standard photometric data is generated automatically. To compile such data manually would be an extremely time consuming and error-prone process.
• Having access to an in-house test facility means that new products can be brought to market more quickly and at lower cost. With PM-NFMS, there's no need to wait weeks if not months to obtain your photometric data.
• Product development cycles are reduced and new innovations tested quickly to establish their feasability. PM-NFMS enhances your ability to innovate and gives you a distinct competitive advantage.

Goniometer Frames for Small, Medium & Large Luminaires

The PM-NFMS goniometer frame is available in three sizes to accomodate different sizes of luminaires. The maximum size and weight of the device under test determine which goniometer frame you will need. As a guide, the medium size PM-NFMS0800 has been used to measure luminiares measuring up to 1.6m linear and weighing up to 25kg. The compact PM-NFMS0400 is suitable for samples weighing up to 5kg and measuring up to 80cm approximately. The minimum sample size that a frame can accomodate is determined only by the field-of-view of the ProMetric imaging photometer and this can be selected through appropriate choice of lens. For guidance on selecting the the right size PM-NFMS goniometer frame for your luminaires, contact Pro-Lite.

The ProMetric CCD Imaging Photometer/Colorimeter

ProMetric imaging photometers are available with a range of sensitivities and CCD pixel resolutions, from 10-bit to 16-bit (the ability to resolve from 1,024 to 65,536 levels of brightness) and from 512 x 512 up to 3,072 x 2,048 pixels. Interchangeable lenses are available to match the field-of-view of the imaging photometer to the size of the device under test. For the majority of applications, the ProMetric PM-1200N-1 represents the best compromise between price and performance. This is a 12-bit (4096 grey scale) photometer with 1,392 x 1,040 pixels and spectral response precisely matched to the CIE 1931 2° standard tristimulus observer function. The internal RGB filter wheel is paired with a neutral density filter wheel which allows the PM-1200N-1 to cope with a wide range of light levels without risk of saturation. ProMetric software for the imaging photometer is also included which allows for the use of the PM-1200N-1 for spatial luminance and colour analysis of sources, including signs and LED arrays.