SOLAR PV CONTROL SYSTEM.pdf
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SENSORS<br />
LED as light sensor<br />
Figure 8: LED used as light sensor for a Robot<br />
An LED can be used as a photodiode used for light detection as well as emission.<br />
This capability has been demonstrated and used in a variety of applications<br />
including ambient light detection and bidirectional communications.This<br />
implementation of LEDs is important because functionality can be added to designs<br />
with only minor modifications, usually at little or no cost<br />
An LED is a diode specifically made for efficient light emission and has been<br />
packaged in a transparent case. If inserted into a circuit in the same way as a<br />
photodiode, which is essentially the same thing, the LED will perform the same<br />
function. As a photodiode, it is sensitive to wavelengths equal to or shorter than the<br />
predominant wavelength it emits. For example, a green LED will be sensitive to blue<br />
light and to some green light, but not to yellow or red light. Additionally, the LED can<br />
be multiplexed in such a circuit, such that it can be used for both light emission and<br />
sensing at different times.<br />
Applications for this technology range from simple ambient light sensors to full<br />
bidirectional communications using a single LED. Applications benefit from the cost<br />
reduction of using the same component for multiple functions.<br />
Ambient light sensors<br />
LEDs have been used as ambient light sensors. For example, a remote control<br />
keypad backlight would be turned on by capacitive proximity sensors only in the<br />
Email: david.irungu@stu.kuct.ac.ke<br />
24<br />
2012
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