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Wireless Sensor and Actuator Networks for Lighting Energy ...

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corresponding ancillary circuitry amplifies the signal from the photosensitive element to<br />

match the input range of the analog-to-digital converter (ADC) on the mote plat<strong>for</strong>m.<br />

The Hamamatsu S7686 silicon photodiode was selected as the photosensitive<br />

element. This specific photodiode possesses sensitivity close to that of human eyes <strong>and</strong><br />

is color-corrected to match the CIE curve. The CIE curve is a color model based on<br />

human perception that was developed by the Commission Internationale de l’Eclairage<br />

(the International Commission on Illumination) committee. The spectral response of the<br />

photodiode is reproduced in Figure 7-1, in which the CIE curve is overlaid.<br />

Figure 7-1 Spectral response of Hamamatsu 7686 photodiode [101].<br />

Since the wireless photosensors are meant <strong>for</strong> being deployed on desktops to<br />

measure workplane illuminance, the normal operating range of the photosensor is<br />

97

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