LED As Light Sensor
An LED can be used as a photodiode used for light detection as well as emission. This capability has been demonstrated and used in a variety of applications including ambient light detection and bidirectional communications. This implementation of LEDs is important because functionality can be added to designs with only minor modifications, usually at little or no cost.
An LED is a diode specifically made for efficient light emission and has been packaged in a transparent case. If inserted into a circuit in the same way as a photodiode, which is essentially the same thing, the LED will perform the same function. As a photodiode, it is sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. For example, a green LED will be sensitive to blue light and to some green light, but not to yellow or red light. Additionally, the LED can be multiplexed in such a circuit, such that it can be used for both light emission and sensing at different times.
Applications for this technology range from simple ambient light sensors to full bidirectional communications using a single LED. Applications benefit from the cost reduction of using the same component for multiple functions.
Read more about this topic: LED Circuit
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