Dimmer Switches – a Guide to Types available and Their Use

The Use of Dimmer Switches

Basically dimmer switches are use to vary the brightness of light bulbs. They are used mainly for incandescant bulbs and halogens, but there will shortly be on the market a compact fluorescent (energy saving) bulb which can be controlled with a dimmer switch, although these bulbs will be relatively expensive. Dimmer switches save energy, in that a bulb dimmed to, say, half power only uses about half the electricity, there being very little consumption in the switch itself. Most cheaper dimmer switches contain a high current variable resistor which is run in series with the bulb. Some more expensive ones dim the bulb electronically, but for normal home use I would recommend the former. Some contain fuses, and if the dimmer switch fails, check if a fuse inside it has blown. This is particularly liable to happen if the bulb blows.

Different Types of Dimmer Switches

The most common is a wall switch, which replaces an ordinary light switch. They are easy to fit. There are 2 terminals on one way switches, and the wires can fit either way round. There are 3 terminals on 2 way switches, usually marked ‘C’, ‘L1’, and ‘L2’. Just connect the wires on the dimmer switch exactly as they were on the original switch. A 2 way switch can be used as a one way one, leaving either the ‘L1’ or ‘L2’ terminal not used. In a 2 way switch system, only one switch is replaced with a dimmer, and this controls the brightness. The other switch just switches the light(s) on or off, the brightness being determined by where the dimmer switch is set.
Pull cord dimmer switches for bathrooms are available. With these, you just keep pulling the cord, until the desired brightness is reached.
In-line dimmer switches for floor and table lamps can be wired into the mains flex. Alternatively, for these lamps, plug-in dimmer swithes are very simple to use. No wiring is involved; the unit plugs into the mains socket, and the lamp plugs into this. Dimming is controlled by a small rotary knob on the plug-in unit.

Considerations When Using a Dimmer Switch

Dimmer switches are rated with maximum and minimum load wattages, say typically 40W to 400W. This means the total bulb wattage that the dimmer switch controls must be within these limits. If using mains halogen bulbs, leave plenty of spare capacity; ideally double the wattage of the bulbs to get the maximum load wattage of the dimmer switch. 12 volt halogen bulbs can give problems with dimmer switches. If you want to use one, make sure the transformer can be used with a dimmer switch and vice versa, otherwise the lights may flicker and there may be an appreciable hum. Your retailer will give you advice on this.
There are commomly two types of dimmer switches – push on/push off and those which click off or on at the end of the knob rotation. The former have the advantage that the previous dimmed setting is maintained the next time it is switched on, but I prefer the latter, as I think they increase bulb life. The bulb is always brought up from zero to full brightness, rather than applying the full voltage to it immediately it is switched on. This more gradual increase is better for the life of the bulb.

Dimming Low Energy Bulbs

These cannot generally be easily dimmed. As has been said above, a compact fluorescent will soon be available which can be used with a dimmer switch, but I think a better option is to buy one which can be dimmed with an ordinary switch. These are already available – see the link below. LED lighting again cannot be easily dimmed at present, but this is generally not very bright, and dimming is usually not needed with these.