Salt Water Dimmer, Resistance Type Dimmer, Light Dimmer

Dimmers

• Different lamps/luminaires produce light with constant brightness once they are switched on.
• For the following spots, the variation of brightness of the lamps is required.

For (i) Photo studios (ii) Stage (iii) Drama theatres (iv) Decorations (v) Various functions.

• The device for controlling the brightness is a "Dimmer".
• Dimmer is an electrical and or electronics device. It basically changes the current or voltage which is the cause of varying brightness of luminaries.

  Let us study the circuit arrangements and operation of these dimmers.
1. Variable Resistance Type Dimmer
1.1 Resistance Type Dimmer

1.2 Salt Water Dimmer
Q. Explain working of salt water dimmer with the help of diagram.
Parts of Salt Water Dimmer

1. Container
2. Fixed contact
3. Moving contact
4. Luminary

Following Figure shows circuit arrangement (a) and photograph (b).

• It makes use of salt water for controlling the brightness of luminary/lamp Figure (a) shows the arrangement of salt water dimmer.

Circuit Diagram of Salt water Dimmer (a)

Salt water dimmer (b)

Construction and operation of Salt Water Dimmer

• Salt water dimmers rely on salinity and distance between metal contacts to control the brightness of the luminary/lamp.
• It consists of a container in which salt water is poured. There is one electrode fixed at the bottom and the other electrode can move up and down.
• The electric supply is connected across these electrodes. Movable electrode is connected in series with the lamp.
• The electric power fed to the lamp can be controlled by the movement of this electrode i.e. by increasing and decreasing its distance from the fixed electrode. As the movable electrode moves upwards, the distance between the two electrodes increases.
• The resistance between these electrodes increases, therefore voltage applied to the luminary decreases, hence the brightness of the lamp decreases.
• As the movable electrode moves downwards, the distance between the two electrodes decreases.
• The resistance between these electrodes decreases, therefore voltage applied to the luminary increases, these the brightness of the lamp increases. The closer the contacts are to each other, the brighter the luminary.
• The effectiveness of the control depends on the smoothness of the movement of raising and lowering the movable electrode.
• Figure (b) shows salt water dimmer used in old days. It consists of number of wheels arranged on a common shaft.
• The wheels can be rotated by moving the control rod. As the control rod is moved, the motion of wheel is transferred to the belt.
• The moving electrode is connected to the belt, thus moving rod also moves. The motion of the moving rod can be controlled with control rod.

Advantages of Salt Water Dimmer

1. Smooth control of brightness.
2. Better control.

Disadvantages of Salt Water Dimmer

1. Operation is not safe.
2. Leakage current can be present.
3. The current can produce toxic chlorine gas flammable hydrogen and oxygen due to chemical reaction in salt water.
4. Considerable attention is required to keep the water level constant.
5. Operating mechanism has to be designed for precise movement to get better control.

2. Dimmer Transformer
2.1 Autotransformer Dimmer
2.2 Two Winding Transformer Dimmer

3. Electronic Dimmer

3.1 Thyristor operated dimmer

3.2 Triac Operates Dimmer