"Light" dark sky 10M? Daytime voltage 1K, with 10K minutes. This voltage is compared by the operational amplifier lm358, so that the transistor is turned on or off and the light is controlled. The assumed led in the figure is a small led with a vcc voltage of 5V. If it is 1Wled, the resistance of the led string can be changed from 1k to 10Ohm. The two resistors "10, 10" in the figure are power resistors, but the power consumption is relatively high. Of course, the transistor can be replaced by a special constant current chip. The triode is assumed to be 90 13. The rheostat in the figure is used to adjust the specific voltage relative to the optical partial pressure. If it is greater than the optical partial pressure, the triode is turned off, and if it is small, it is turned on, and the skylight1k. The voltage at point A in the figure will become low, so LM358 outputs a low level, the transistor is not conductive, the lamp goes out, and vice versa.

Of course, there is a way to achieve different led brightness without lighting, and of course this circuit is also used, but negative feedback needs to be introduced. Of course, this matter is another matter.