Twilight sensors

An optical sensor that combines the functions of a twilight sensor and a solar sensor in one package is referred to as a light sensor. Light sensors have been on the market since 1997. 

Fig. 7.13.9 and Fig. 7.13.10 show a light sensor assembly photographs and angular responses for both the solar sensor and the twilight sensor. The sensor is set to reach its maximum output when the sun is at an elevation about 40°, which is when the driver feels hottest. 

Current mirror distributes the photodiode output current to the solar sensor output and the twilight sensor output. 

Circuitry for setting intercepts for piecewise-linear characteristics sets the intercepts for piecewise-linear characteristic of the twilight sensor output. 

Circuitry for setting gradients for piecewise-linear characteristics utilize a three-input OP amplifier to set the gradients for piecewise-linear characteristic of the twilight sensor output. Since the three inputs are at the lowest transistor base potential, the sensor s characteristics are as shown in Fig. 7.13.14 when the inputs are VI, V2, and V3. 

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