Guide to Dimming

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R Hamilton & Co Ltd is one of the leading manufacturers of dimmers in the UK and markets its products under the Litestat brand name. The following information is designed to help you decide which is the best solution for your particular installation.

Types Of Dimmers
Dimmers can be divided into three main groups depending on the light source being controlled.

Resistive
These are designed to control lamps that have a filament, which emits heat and visible light. Typical lamps are standard GLS incandescent, Mains halogen.

Inductive
These dimmers are designed to control light sources which use wire wound components in the form of transformers. An example of this would be low voltage lighting.

Fluorescent
This light source requires a ballast for the lamp to operate.

Resistive dimmers - are rated by the maximum recommended wattage the unit will control. Overloading the dimmer or using it to control Inductive loads can cause damage to the dimmer.

Inductive Dimmers - are rated as VA (Volt amps) and have already been de-rated to allow for the current-in rush from the transformer.

Fluorescent dimmers - it is recommended that where fluorescent installations need to be dimmed, a High frequency analogue 1 – 10 volt ballast is used. This will result in lower dimming levels, smoother dimming control and a reduction in RFI.

Dimming of Electronic Transformers - today most electronic transformers can be controlled by a resistive type dimmer. However there are still some electronic transformers having the characteristics of an inductive load.

What is dimming?
Dimming is the reduction of the power into, and therefore out of, a light source.

What are the advantages/uses of this?
Reducing the power into the light source reduces the power in the circuit. This will lead to a saving of energy and hence lower running costs. As a result, the life expectancy of the light source is also increased. Again this lowers the running costs of the system by reducing the amount of maintenance that a system requires.

Operation
Two-way versions have push on/off operation. When switched on the dimmer selects one of two contacts L1, L2.

The two-way version is suitable for two-way switching as found in stairways, halls, corridors etc.

SPECIAL NOTE: Only one two way dimmer can be connected in a two way circuit. The other control point must be a two-way switch.

For tungsten/incandescent loads, providing the total load on the circuit is within the rating of the dimmer and the dimmer selected is suitable for tungsten/incandescent loads, there should be no problems associated with the dimming. (These dimmers are not suitable for control of energy saving fluorescent lamps.

The need to de-rate a dimmer
When using Mains Voltage Halogen lamps such as GU9, GU10, GZ10 and Linear halogen lamps, dimmers should be de-rated by 25%.

This helps compensate for the additional load due to arcing at the end of the lamp life cycle. This extra load can damage the dimmer. Where possible it is better to use branded lamps such as those produced by GE, Osram, Philips and Sylvania. Generally these have an in-built thermal link and, should the lamp filament short out, the thermal fuse stops the inrush of current which can damage a dimmer. (LIF Technical Statement No.25). Many cheaper imported lamps do not have this thermal link.

In some cases the number of dimmers on a plate must be de-rated because of the heat generated during normal operation.

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