|Warning: Please be careful when experimenting or working on this circuit as the voltage in the circuit is 230V.
On many occasions full illumination is not needed especially at bed time. Instead of turning off the lamp completely with the common switch, dimmer switch gives you power to reduce the illumination to the level you want. Aside that, it adds real beauty to your home and save you energy (money).
The technology of light dimmer is based on adjusting the voltage entering the lamp which in turn varies the brightness of the lamp. In the early days, light dimmer systems make used of autotransformer just exactly what is in the control unit of a ceiling fan, or power resistor to control the voltage that enters the lamp. The problem with them is that they are bulky, expensive and have poor efficiency as they waste much energy inform of heat.
Modern day dimmers make use of solid state switches (triac and diac) to control the voltage entering the lamp. Controlling of voltage entering the lamp is done by chopping out part of the AC wave-form of the supply voltage. This is achievable by varying the triggering angle of the triac as
illustrated with the figures below.
Triac triggered at 30 degree
Triac triggered at 90 degree
The circuit below is a simple dimmer circuit . Network of R1, R2, VR1, C2, C3 and Q1 controls the triggering angle of the triac by varying the variable resistor VR1. Triggering of the triac in the middle of AC phase causes fast rising current surges. This results in radio frequency generation and when triggered at 90 degree it is highest. Network of C1 and L1 forms a simple radio frequency interference filter which filter out the interference.
When VR1 is turned to maximum, the lamp goes off and it is full when VR1 is turned to 'zero'. So varying VR1 from 'zero' to maximum decreases the brightness of the lamp till it goes off.
Light dimmer circuit
1 step light dimmer circuit
Automatic street light circuit 1
Automatic street light circuit 2