The issue of determining the variation in colour LED-to-LED on an LED board (typically one that forms the basis of a luminaire) is one that is frequently raised by customers of the Photometric Testing laboratory. Measuring the colour and brightness (luminance or luminous intensity) of each LED on a circuit board that may contain hundreds of LEDs is possible but can be very time consuming. Fortunately, here at Photometric Testing, we use several Radiant Zemax ProMetric Imaging Colorimeters, supplied by our sister company Pro-Lite Technology. A ProMetric imaging colorimeter makes the job of measuring the colour of each LED in an array impressively simple, almost as simple as taking a picture. Which is what the imaging colorimeter does, as it happens!
Think of the imaging colorimeter as like a high resolution digital still camera, except that the pictures that it takes are photometrically and colorimetrically calibrated and possessed of a photometric sensitivity and dynamic range that exceeds even that of the human eye. With up to 16 million pixels in the camera's CCD sensor and with up to 16 bits (65,000:1) dynamic range, a ProMetric imaging colorimeter can accurately record the colour and brightness of literally thousands of LEDs in an instant, thus making it possible to automatically analyse an LED array in real time in a production environment. The picture below shows a ProMetric image of an LED array with software-applied virtual "points of interest" detectors applied to report the photometric brightness and correlated colour temperature of three of the emitters.
Templates (pre-determined grids) of analysis points can be stored in ProMetric imaging colorimeter software to simplify the analysis of different designs of LED arrays, so all the operator has to do is align the imaging photometer to the device under test, choose the appropriate point of interest set, record an image and review the analysis report to determine whether the LED array in question meets defined pass / fail criteria. You can set upper and lower limits both in terms of brightness and CCT that the individual LEDs or the board as a whole have to meet. You will also know whether any LEDs on the board are unlit. For automated production line testing, a software API (programming interface) allows the ProMetric imaging colorimeter to be integrated into an on-line test station. Not only does the imaging colorimeter guarantee the colour consistency of the LED array, it also replaces human visual inspection, which can be both subjective abd unreliable and of course extremely unpleasant to perform, given the glare from high brightness LEDs.
Photometric Testing is pleased to offer contract testing of LED boards. Please feel free to call us on
+44 (0) 1242 701300 for a quotation, or use our on-line enquiry form.