Osram Opto Semiconductors has added phototransistor SFH 3711 to its range of ambient light sensors for automotive applications. The spectral sensitivity of the sensor has been designed so that its brightness measurements closely match the sensitivity of the human eye. The SFH 3711 is therefore ideal for automatically switching on low beam at dusk or in tunnels – a function which will be required by the European Union on new vehicles from 2016.
Excellent infrared suppression
The most important characteristic of the SFH 3711 is its spectral sensitivity, which is almost identical to the V-lambda characteristic of the human eye. The SFH 3711 registers light in the 470 to 670 nanometer (nm) range, with a maximum at 570 nm. For infrared light with wavelengths above 750 nm its sensitivity falls to less than one percent. The sensor therefore reliably switches low beam on even if the setting sun is still sending out red light and infrared light, which is invisible to our eyes. This property means that in terms of performance the SFH 3711 comes close to the SFH 5711 photo IC which is used in top-of-the-range vehicles for extremely accurate ambient light measurements.
Good price/performance ratio
The sensor in the compact 2 mm x 1.25 mm x 0.8 mm Chipled package has been in use for some time for consumer applications such as for controlling display backlighting on mobile devices. Now that it is qualified for use in vehicles the SFH 3711 represents an economical solution in this sector for registering ambient brightness with a high degree of accuracy. Its excellent price/performance ratio makes it an ideal entry-level system, particularly for mid-range and compact vehicle classes, as a means of providing ambient light measurements for automatically controlling display backlighting and for implementing automatic activation of low beam headlights which will be a requirement on new vehicles from 2016.
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