Using a common benefit of photo voltaics LED, the circuit can recognize a different output darkness and light. This circuit is used J-FET for receive signal to buffer from LED ,About Output voltage, we used IC 1458 or LM1458 , while in the dark is about 7 volts and the drop about 2 volts in full sun. This is the figure of the circuit;
The LED voltage buffered by a junction FET transistor and then applied to the input of an operational inverting amplifier with a gain of about 20 minutes. This is a variation of about 5 volts of darkness and light. You can adjust the 100K potentiometer to set the range of output voltage.