Automatic street light | Light sensor | Street light without battery and relay

Other Hardware General Electronics
1

Hey I saw a video few days ago

Would someone rectify it, i mean how is his circuit working
i tried it but it was not working as shown in video
is this video fake ?

2

Not recommended, this can be dangerous.

The triac is being controlled by a diac with the LDR controlling the trip point. It can work... it doesn’t need a battery because it’s pulling power from MAINS. Again be careful you can be seriously harmed with this circuit.

3

Here is something similar but with a simple schematic:

4

wolframore:
Not recommended, this can be dangerous.

The triac is being controlled by a diac with the LDR controlling the trip point. It can work... it doesn’t need a battery because it’s pulling power from MAINS. Again be careful you can be seriously harmed with this circuit.

when ldr resistance is high and all the current will go through resistor and then diac and then triac right
and as diac breakdown voltage is 32v that mean whenever ac cycles comes below 32v the triac turns off even when the ldr resistance is high
am i right ?

5

The LDR internal resistance increases when there is no light, this causes voltage to develop across it as it is a voltage divider with the other resistor. When this voltage is higher than the breakover voltage of the diac, the diac latches on which switches on the triac. The diac once it turns on the triac,is no longer in play. The triac will stay on until the zero crossover is reached. The process repeats on each of the negative and positive cycles. Using a potentiometer (not recommended again due to 230 VAC MAINS voltage unless it’s in an insulated case) You could control the intensity and can be a dimmer. It controls the pulse width of the alternating 60 Hz (or 50 in some countries) sine wave.

6

Circuit should work indeed but any modern bulb (CFL or LED) may react very poorly to it until the darkness is complete and the TRIAC is pretty much fully on. In twilight there'll be phase cutting, starting at 50%. Both videos (links in the OP and #2) use obsolete incandescent lamps.

I wonder what the purpose of the diode is in the project in the link of the OP.