I’ve been working on a project that will allow me to determine the number of sun hours available in a given spot, and track that over time, as a component of solar power installation design. The idea is to get a light detector in the sun, record the number of hours it is lit at full intensity, and map that to photovoltaic equivalence. One could use a pv cell, but there are other alternatives. The CdS cell, photodiode and others come to mind. We will try each of these methods and post our results, meanwhile, here is a great tutorial on the options:
http://www.electronics-tutorials.ws/io/io_4.html
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Light Sensors are used to measure the radiant energy that exists in a very narrow range of frequencies basically called “light”, and which ranges in frequency from “Infrared” to “Visible” up to “Ultraviolet” light. Light sensors are passive devices that convert this “light energy” whether visible or in the infrared parts of the spectrum into an electrical signal output. Light sensors are more commonly known as “Photoelectric Devices” or “Photosensors” which can be grouped into two main categories, those which generate electricity when illuminated, such as Photovoltaics or Photoemissives etc, and those which change their electrical properties such as Photoresistors or Photoconductors. This leads to the following classification of devices.
For more info, see http://www.ecs.umass.edu/ece/m5/tutorials/CdS_Flex_Sensor.html