Light Operated lamp switch using DIAC and TRIAC

Various electronic projects using LDR (Light Operated Resistor) are already posted on bestengineeringprojects.com. Now, here is another simple project using LDR called a light-operated lamp switch using DIAC and TRIAC. This circuit utilizes very few components and is so simple that anyone can understand it.

Circuit Description of Light Operated Lamp Switch:

The circuit of light operated lamp switch utilizes a diac and a triac as semiconductors and LDR as a sensor. LDR is a type of variable resistor that changes its value according to the intensity of light falling on its surface. At dark, its resistance increases up to mega ohms, which does not exit triac and hence it does not conduct.

When LDR is illuminated using any light source (like torchlight), the resistance of LDR suddenly decreases and further drives the triac as a result switching on the lamp. LDR is so adjusted that the light received from the lamp keeps resistance low. So, the lamp remains continuously ‘ON’. Once the lamp is ‘ON’ it can be switched ‘OFF’ again by interrupting the light falling on LDR, either by waving a hand in front of it or by interrupting the power supply to the circuit for a   moment.

Check out other interesting projects using LDR posted on bestengineeringprojects.com

1. Photoelectric switch using ne555
2. Self Resetting LDR Alarm using Timer IC 555
3. Automatic Light Operated Switch using LDR and IC741
4. Automatic Fence Lighting with Alarm
5. IC 555 Based Automatic evening lamp

PARTS LIST OF LIGHT OPERATED LAMP SWITCH USING DIAC AND TRIAC

Resistor (all ¼-watt, ± 5% Carbon)

R1 = 10 KΩ, 1W R2 = 470 Ω, 1W

Capacitors

C1 – C3 = 0.1 µF/400V (POLY)

Semiconductors

DIAC = D-84 TRIAC = 8T44A (4A,400V)

Miscellaneous

LDR RFC = 15 turns of 18 SWG wire over an insulated ferrite rod. BULB = 230V