Is this LDR and TRIAC circuit advisable for real time application?
Disadvantages: For one, it won't typically work at all. Typical gate trigger current for the BT136 is 2.5mA/5mA in quadrants I and III respectively.
The 220K resistor will conduct 1.4mA at the very peak of a 220V waveform, insufficient to turn the triac on in either quadrant. At 110V or at cold temperatures or with a particularly numb sample of BT136 things are considerably worse.
Advantages? I guess it conserves energy.