Eye protection light controlled by TV

The TV on-off signal pickup and signal amplifier are composed of electromagnetic coil L, transistors VT1, VT2, etc. respectively.
We know that when the TV is turned on, the TV power cord will generate a 50HZ electromagnetic field around it due to energization. The coil L
picks up this 50Hz alternating magnetic field and generates a corresponding electrical signal, which is output by Cl and passes through the VT1 and VT2 two-stage amplifiers. After amplification,
it is sent to the rectifier composed of VDI, VD2 and C4 through C3 for voltage doubling rectification. The corresponding
DC . This voltage is divided by R5 and R6 and added to the base of VT3 to cause VT3 to conduct When it is turned on, the thyristor VS can obtain the trigger current
and turn on, and the lamp H lights up. If the TV is turned off, due to the interruption of the AC signal in the power line, there is no alternating signal output from coil L , the DC voltage
at both ends of C4 disappears, VT3 is cut off, and vs has no trigger current. When the alternating current crosses zero, it is turned off and the lamp H goes out. If it is a remote control color TV, although there is still AC current flowing in the power cord after the remote control is turned off, its signal strength is greatly reduced. The DC voltage at both ends of C4 is very low. After being divided by R5 and R6, it is not enough to maintain VT3 conduction, so The light H will also go out when the remote control is turned off. The light control circuit is mainly composed of photoresistor RO, etc. During the day, RO is exposed to natural light indoors and exhibits low resistance, which causes the DC voltage at both ends of capacitor C4 to attenuate greatly, so VT3 will remain in the cut-off state, and the lamp H will not light. Bright. Only at night, RG is high resistance, and its presence has no effect on C4, so the circuit can work normally.     The value of the capacitor C4 of this machine is very small, only l uF. Its purpose is that the lamp H can light up immediately after the TV is turned on. If the C} capacity is increased to 47 uF, after the TV is turned on, there will be a delay of tens of seconds before the light turns on because C4 has a charging process. But after the TV is turned off, because C4 has a discharge process, there will also be a delay time of tens of seconds before the light H goes out. It is up to the reader to decide whether to delay the time.