LED Users - How to Get Angular Intensity, Colour and View Angle Data Quickly

21 Feb 2006

It’s rare for a genuinely novel piece of optical test equipment to be invented – but that’s what Radiant Imaging of Seattle have done with their new ProMetric Imaging Sphere™ - so reports their UK dealer Pro-Lite Technology.

The IS-LI is the only non-moving-part goniophotometer on the market – it measures the luminous intensity distribution from an LED over a complete hemisphere (2 pi steradians) in a couple of seconds. It does this without any moving parts. It also provides the variation of colour (as well as colour temperature and colour difference) with view angle into the bargain. To most engineers, this might seem too good to be true. Well, prepare to be impressed… The Imaging Sphere works like this: an LED (or any other small light source, or indeed flat panel display) is positioned in the centre of a 50cm dome; the LED creates an illumination pattern on the inside of the dome; a small, convex mirror placed to the side of the LED images the illumination pattern on the inside of the dome; finally, a ProMetric 512 x 512 pixel CCD-based imaging photometer views the mirror, and hence views the entire hemispheric illumination pattern from the LED. The result? The ProMetric camera records the intensity and view angle variation for all angles in a single measurement that takes just a second or two. To which most people will respond: “why didn’t I think of this before?” Radiant won’t take all the credit. The Imaging Sphere was first developed by Royal Philips Electronics in The Netherlands as a tool to match the appearance (and not just the colour) of plastic parts being used in its consumer electrical products. That’s another use for the Imaging Sphere by the way – measuring the reflectance as a function of angle (and hence BRDF) of materials. Anyway, back to light source characterisation – Philips have licensed the Imaging Sphere to Radiant Imaging who have applied their considerable expertise in software development and light source characterisation to provide a turn-key measurement system that gives LED producers and users a truly productivity-enhancing instrument that will reduce development costs, allow LED-based products to get to market faster and improve device performance into the bargain. The Imaging Sphere was first demonstrated in the UK at the Display Testing Seminar held by the DTI’s UK Display Network (www.ukdisplay.net) in Bletchley Park on January 18th 2006. A group of over 30 delegates heard Radiant Imaging’s founder and CEO Ron Rykowski talk about the applications in display and LED testing of his ProMetric Imaging Photometers and Imaging Sphere. Pro-Lite received its first Imaging Sphere order the day after. Why all the fuss? Well, the precise determination of where the light from an LED goes is the first step in designing high quality LED-based lighting systems. All LEDs vary. Although this information has been available in the past, it required the use of a slow, cumbersome and expensive goniophotometer. The Imaging Sphere renders such an antiquated approach obsolete overnight – it is faster, easier to use, more reliable (no moving parts, don’t forget) and much cheaper. ProMetric system software supports automated and/or customised measurements, as well as data analysis and display functions. Data can be displayed as isometric plots, cross-sectional graphs, radar plots, bit maps and colour graphs. The system is designed for use with LEDs and other small light sources with outputs from 0.1 to 10 million candelas and provides an angular accuracy of 0.25% (2mm DUT) and a resolution of 0.5 degrees. The angular range is 0-360 degrees (azimuth) and 0-85 degrees (inclination). About Radiant Imaging Radiant Imaging, Inc., founded in 1981, is the worldwide leader in imaging systems for light and colour measurement, and illumination engineering tools and services. Radiant Imaging’s technologies are focused on providing lighting and display system manufacturers with enhanced design capabilities, greater product development efficiency, improved manufacturing productivity and increased competitive effectiveness in the world marketplace. Radiant Imaging’s three major product areas are the ProMetric® light and colour measurement systems, Radiant Sources® light source characterization systems and source data, and Application Engineering Services to support development of application-specific solutions incorporating ProMetric® technology. About Pro-Lite Technology Pro-Lite, founded in 2002, serves as the Radiant Imaging distributor in the United Kingdom and Ireland. Pro-Lite offers a wide range of productivity-enhancing equipment for optical radiation measurements as well as integrating spheres, imaging photometers, detectors for the UV to FIR spectral range, lasers that operate from 157nm to 4.5 microns, a full range of laser test and measurement equipment, acousto-optics for laser modulation and control, laser safety eyewear and precision opto-mechanical building blocks. Further Information Robert Yeo Pro-Lite Technology LLP Innovation Centre University Way Cranfield MK43 0BT Bedfordshire England Tel: +44 (0) 1234 436110 Fax: +44 (0) 1234 436111 info@pro-lite.uk.com www.pro-lite.uk.com