Electronic Design

Light Sensors

Sponsored by: <A HREF="http://www.microsemi.com" TARGET=_blank>MICROSEMI CORP.</A>

What are the most common types of light sensors?

Two of the most common light sensors are phototransistors and positive-intrinsic-negative (pin) photodiodes. Both generate signals that vary with ambient incident light levels and are most commonly used in display backlighting applications. A phototransistor's output response is typically a voltage, while a photodiode's output is typically a current (Fig. 1).

Why is the human eye response critical in an automatic brightness control application?

The response of the human eye to light peaks at a wavelength of about 550 nm, and it cannot detect infrared or ultraviolet light. As a result, sensors that react to infrared and ultraviolet will make adjustments erroneous to the human eye. Because of this, most light sensors must eliminate infrared and ultraviolet sensing with complex and costly optical filters.

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