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The circuit is shown in Figure 27.6. The TCC is a photocell original. The 555 is used as a hysteresis comparison and drive trigger circuit, and the LED is an indicator light. The BCR is used as a light switch. ZD is a group of lighting fixtures. The DC working power supply is powered by a capacitor step-down mode, and a simple half-wave rectification and Zener diode voltage limiting are used to obtain a DC voltage of about 10V.
Photocells are commonly used as photometric components as well as power supplies for micropower circuits and aerospace satellites. When it is used as a power source, it collects a photo-generated voltage that produces a proportional and light intensity relative to the negative terminal. It can supply about 100μA or more per square centimeter, and the open circuit voltage is about 300mV. Here, it is used as a photodiode, plus a reverse bias. The reverse current is also proportional to glare, and the range of variation is from 1μA to above 100μA, and the dark current is usually less than 1μA.
During the daytime, the TCC is illuminated, and its reverse current increases, causing the potential of the 555th 2nd and 6th feet to drop. When the light intensity reaches a certain value, the 555 output 3rd and 7th feet are turned to a high level, so that the LED and the BCR are turned off, and the ZD is turned off.
As night falls, the TCC is weakened by illumination, and its reverse current is also reduced, causing the potential of the second and sixth feet of 555 to rise. When the light is dark to a certain extent, the output of 555 third and seventh feet is turned low, the LED is illuminated, and the BCR is turned on, so that the ZD is energized.
There are no two potentiometers (100kΩ and 1MΩ) in the figure. The 100kΩ potentiometer is used to adjust the hysteresis of the ZD turn-on and light. The 1MΩ potentiometer is used to adjust the light control sensitivity. With these two potentiometers, you can adjust to any light level to turn on and off the lights, and adjust them according to actual requirements.
It is required to withstand voltages of 500V or more, and its current capacity can be used up to 40A, and it can control lights up to 6kW.
Any photocell or solar cell can be used, and the solar cell on the used electronic calculator usually does not fail, and is a good light sensing component. 
Highly sensitive automatic lighting circuit analysis
This automatic lighting control circuit uses a photocell as a light intensity detecting element, which has the characteristics of high sensitivity and large light detection range. Fully automatic control can be achieved with a simple control circuit.