Electronic Design

Ambient Light Sensor Sees With A “Human Eye”

A new ambient light sensor from OSRAM Opto Semiconductors is well suited for mobile devices and digital cameras. In addition, the ALS SFH5711 will benefit automotive cockpit dimming and headlight control applications. OSRAM claims the light sensor accurately matches or imitates the sensitivity curve of the human eye, enabling displays and their related brightness range to be adjusted more precisely than ever before.

The ALS SFH5711 is an enhanced ChipLED version of OSRAM’s SFH3410 sensor, which traditionally has been used in light dimming applications. It has the added benefit of a small yet robust surface-mount package, which offers the cost savings required for consumer applications and delivers excellent optical performance.

Its "human eye" properties were developed through a new material system that replaces traditional silicon. A logarithmic amplifier enables a substantial brightness range (from 3 lx to more than 30,000 lx) to be detected with great accuracy. The sensor’s logarithmic—rather than linear—output maximizes precision over the complete range of brightnesses, from twilight to sunlight. In a linear design, the system switches back and forth between various resolutions using different resistances. The SFH 5711 does not require this resistor grid for gain switching, saving board space.

The sensor’s spectral sensitivity is 560 nm, thus mimicking the location where the human eye is most sensitive. The V-lambda characteristic of the ALS represents the curve on the wavelength spectrum where the human eye sees color. By automatically imitating the characteristics of the human eye, and doing so quicker than the human eye, the ALS SFH5711 is suitable for adjusting the brightness of displays and other such components for optimum readability in constantly changing light conditions.

Using a low supply voltage of 2.3 to 5 V, the sensor is energy efficient and ideal for daylight sensor applications where backlight displays must be constantly monitored and/or adjusted. The ALS SFH5711 sensor also prevents the rapid onset of eyestrain often connected to the use of computer laptops and computer monitors' LCDs, a traditional problem if the display is too bright in a dark room. The newest ALS also is an ideal solution in automotive applications where it reads ambient light levels and switches headlights on and off.

ALS SFH5711 measures 2.2 by 2.8 by 1.1 mm. It’s currently available and is sampling for about $0.65 each.

OSRAM Opto Semiconductors

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