Light Dimmer

The lighting source (i.e. bulb, tube light) glow according to their specified watt rating. If we need more light then we have to use high watt bulb at the same place if we need low light we have to replace high watt bulb with low rating. But What if there is not necessary to change i.e. different brightness obtained from same source. Here is the simple but effective project which control brightness according to our use from the unchanged light source.

Working of the circuit Light Dimer

The basic principle of light dimmer is based on phase control. The variable resistor VR2 is main controller of the circuit Light Dimer. From main supply capacitor C2 get charges which trigger DIAC D1. VR1 is used for fine brightness controller which control brightness to lower level. R2 and C3 used to overcome interference problem.


Resistors (all ¼-watt, ± 5% Carbon)

R1 = 68 KΩ

R2 = 270 Ω

R3 = 10 KΩ

VR1 = 100 KΩ

VR2 = 500 KΩ


C1, C2, C= 0.33 µF/400V


TR1 = Triac BT136

D1 = Diac ER900

NOTE: Here in this circuit DIAC can be replaced by transistor without any change in circuit as shown in figure 2. Transistor BC148 is used instead of DIAC used in this circuit. For using transistor instead of DIAC Base terminal most not connected or for more safety you can break base terminal and remaining terminal (collector and emitter) is connected without caring of polarity i.e. we can connect any terminal. We can also use diode as DIAC as shown in figure 3.

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