Covert light for clear images – infrared illumination for camera systems
IRED in the medium power range
Picture 1: Systems for number plate recognition take several photos per second
Typical examples of the medium power range are Power Topled with highly efficient emitter chips in thin-film technology. For more narrow emission angles of +/-15° and +/-25° are compact SMT devices with integrated lenses available. In continuous wave operation a current of 100 mA is admissible. Also in pulsed operation, Power Topled facilitate compact and powerful illumination units. They are particularly well suited for applications with a lower duty-cycle, e.g. Automatic Number Plate Recognition (ANPR) at gates, where only a few pictures per second are taken. Pulsed operation also facilitates synchronizing illumination and exposure time, thus reducing power consumption. Combined with the Nanostack technology for 850nm emitters – another recent development by OSRAM Opto Semiconductors, which realizes two light-generating pn-junctions per chip – Power Topled yield a record-breaking power. A Power Topled with Nanostack supplies almost double the amount of light and yields an optical power output of 560 mW at 0.7 A in pulsed operation. Thus not only the number of IRED per illumination unit drops, but designers can also increase the brightness of existing Power Topled systems without difficulty by using identical IRED devices with Nanostack.
Powerful IRED
For developing high-power IRED, OSRAM Opto Semiconductors could benefit from its LED illumination technologies. The result is a large variety of devices featuring an optical power in the 1-Watt range. The IRED are based on chips with a size of 1mm² in modern Surface Mount Technology (SMT) packages. Devices with one Nanostack-chip only supply an optical power of almost 1 Watt. Since chips in thin-film technology emit almost all their light on the top-surface, multichip devices like the OSTAR Lighting yield a power of several Watt.
Picture 2: A broad range of lenses is available for many high-power IRED.
The infrared Platinum Dragon more and more replaces the conventional cascades of radial IRED. With its extremely low thermal resistance the device is particularly well suited for continuous operation in which the 850nm version supplies more than half a Watt optical power at 1 A. A range of several 10 meters can be reached using the classical Dragon design without lens. For longer distances, a large variety of lenses is available [4]. Dragon IRED are also available in Nanostack technology, supplying almost double the power. It allows designers to easily upgrade existing systems or to reduce the number of components. In case the size of the system is crucial, the infrared Oslon is a suitable alternative. At present it is the smallest IRED in the category of more than 1W optical power. This device produces a +/-45° beam, therefore coupling more light into external optics. Oslon is also a suitable alternative to Power Topled designs with external optics. For long-distance systems, the 6-Chip-IRED OSTAR Lighting is a compact and elegant solution, supplying 3.5 W light at 1 A in continuous wave operation.
Picture 3: IRED with one or more Watt power: Platinum Dragon, OSTAR Lighting and Oslon
Thermal management:
The higher the optical power of an IRED, the more heat it will develop. Modern high current packages very efficiently dissipate heat from the chip. Often an additional heat sink at the board becomes necessary. Alternatively a switch from continuous wave to pulsed operation would reduce the average heat. OSRAM Opto Semiconductors has compiled information on the dimensioning of suitable heat sinks and on the development of illumination designs in an application note about high power emitters [1]. OSRAM also supports designers when determining the maximal permissible duty cycle for a certain design, and it provides calculations for thermal management, reliability or operating life.
Picture 4: Many designs with powerful IRED require external heat sinks.
Eye safety:
Under certain circumstances modern IRED with high optical power output may imperil the eyes. Provided they are not operated with external optics, infrared Dragon, Oslon and OSTAR throughout remain below the respective critical ratings if operated under nominal conditions. Narrow-angle lenses, however, may cause high radiant intensities which are hazardous to the eyes. In general, with each system the eye safety should be considered. OSRAM Opto Semiconductors has compiled useful details on this topic in an application note [2] and additionally provides simulation calculations for eye safety.
Conclusion
Powerful IRED facilitate compact illumination units for video and CCTV systems on infrared basis. They substantially reduce the cost for packages, optics, reflectors and production. OSRAM Opto Semiconductors holds a leading position in the field of infrared LED illumination and supports manufacturers with ongoing power enhancement and comprehensive application know-how.
Literature
[1] High Power Emitters for Illumination Applications, Application Note, OSRAM Opto Semiconductors
[2] Eye Safety of IREDs used in Lamp Applications; Application Note, OSRAM Opto Semiconductors
[3] Comparison of LED Circuits, Application Note, OSRAM Opto Semiconductors
[4] Vendor portal for LED lighting (suppliers of metal core boards, heat sinks or lenses for current LED devices are listed): www.ledlightforyou.com.
About the author: Walter Rothmund is Senior Marketing Manager Automotive & Consumer, Infrared Components for Osram Opto Semiconductors.
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