Overview of the Light Switch

Light switches employing quick break technology (see below) are used throughout the world to control lighting circuits. They can be configured to operate several different lighting spaces from a single location, and be integrally linked to motion sensors to provide automatic lighting - useful in security/intruder detection - and in large spaces such as manufacturing complexes, hospitals, large hotels/apartment complexes and corporate buildings.

They have several designs, amongst them the toggle switch, the rocker switch, the dimmer switch and the push-button switch.

 

History

Early electrical switches before 1884 had a major flaw: the switch’s contacts didn’t open or close sufficiently rapidly to prevent destructive electrical arcing from occurring. This shortened the working life of the switch by badly pitting the surface of one contact and coating the surface of the other in a non-conductive residue.

But the electrical engineer John Henry Holmes, who owned an electrical engineering business in the Shieldfield district of Newcastle upon Tyne, had been experimenting with electrical lighting circuits in the late 1880s, and installed Newcastle’s first domestic electrical lighting circuit into his father’s house in 1883. The following year, he applied some of the lessons he'd learned to tackle the contacts problem and came up with a simple but revolutionary solution: quick break technology. This new switch had a snap on, snap off feature, which meant that the contacts would spring apart in an instant or snap together exceptionally rapidly when the switch was thrown. Arcing virtually disappeared, and Holmes’ technology is still widely used in literally billions of light switches across the world in the twenty-first century.

By 1917, Holmes’ quick break technology was incorporated into a new design for a light switch: the toggle switch. This was the brainchild of U.S. inventors William J. Newton and Morris Goldberg and remains a ubiquitous design to this day.

Some modern light switches are activated simply by touching them, either by making light physical contact with a glass touchscreen or a touch-sensitive metal plate (numerous free-standing table lamps have this technology incorporated into them as well).

Due to the durability of Holmes’ original design, however, light switches tend to be replaced infrequently, an event usually occasioned by the need to re-wire an older building to keep up with modern electrical equipment and lighting.

A new generation of touch sensitive switches and lamps are now available which do not depend on any form of mechanical action to be operated. Instead of actuating via the flip of a toggle or the push of a button, these switches commonly use electrical discharge from the human body (body capacitance) to function. Another form of touch switch is the resistance version, which responds to differences in electrical resistance between two conductive plates upon human touch. The third class of touch switches – piezo switches – activate lighting in response to the minute bending of a thin piece of piezo ceramic upon touching. This is typically positioned behind a decorative plate of some sort which can be made from a huge range of different materials. Typically, a force as little as 1.5N will be sufficient to activate a piezo switch even when the ceramic layer is placed behind a relatively rigid material such as stainless steel.

 

Technical aspects

When the contacts of a light switch are in the open position, the switch offers virtually infinite resistance to the conductance of electrons, effectively breaking the lighting circuit. When in the closed, position however, resistance plunges to virtually zero. No matter how instantaneous it might appear to the human eye, the transition between open and closed states always involves a short period of partial contact, during which resistance reaches an intermediate level between two absolutes, zero and infinity.  Brief though it may be, it is sufficiently long for heat to be generated, and if the period of contact exceeds an upper limit, this heat can be fierce enough to weld the contacts together.

For this reason, still employing the quick-break technology developed by Holmes in 1884, mechanically-actuated light switches are designed to ensure that their contacts are in touch with one another for the tiniest period possible. Typically a spring made of hardened beryllium copper alloy is used in smaller switches; when maintained under stress by the switch design, it stores potential energy. At a certain point (when, say, the switch’s toggle is moved beyond a particular position) the potential energy ‘snaps’ into kinetic energy and very rapidly effects the transition between open and closed states. In this way, excessive heating is prevented and the working life of the switch is prolonged.

The light circuit’s electrical inductance energy will escape in the form of an electrical arc just as contacts begin to separate, a phenomenon which has the potential to damage the switch by extending the period of transition and intensifying the amount of heat generated. Inevitably, even with quick-break design enabling exceptionally rapid opening and closing, light switches have a finite working life and will eventually need to be replaced. However, their functioning can be prolonged by ensuring they are fitted to circuits for which they have been intended: they are manufactured in different durabilities depending on the magnitude of the current they permit or break, as well as the voltage and wattage of the system. Placing a switch designed for one specific combination of current, voltage and power into a higher-rated one for which it was not intended will ruin it especially quickly.

For durability, reliability and safety, light switches are manufactured in such a way that contacts are held forcibly together upon closure and break apart rapidly upon opening, irrespective of user manipulation. These switches can, however, be deliberately misused to hold them in extended transition states, which ultimately corrupts the beryllium copper spring and destroys the quick-break action.

 

Product application - where the light switch is used in manufacturing

Thanks to the advent of the light switch, easily controlled electrical lighting circuits became available for large manufacturing spaces, displacing potentially dangerous and ineffective gaslight and candle-light predecessors. Vast lighting areas can be differentially controlled from different switches, and light switches can be linked to motion sensors to provide automated lighting in environments as diverse as public lavatories, warehouses, hospitals, schools/educational institutions and factories.

 

How the light switch differs from other switches

Light switches are rated during design and manufacture for specific deployment in lighting circuitry. They may not be used in power mains circuits, or in circuits carrying greater voltages, current and power than for which they have been specifically rated, without risk of severe degradation and malfunction.

 

Current product advantages and limitations

Quick-break technology has remained a tried and tested means of conserving the working life of light switches since its invention in 1884. However, mechanical operation and arcing will inevitably cause a degree of wear and tear, limiting the working life of any mechanically operated light switch.

 

Where necessary, suitable alternatives

The new generation of touch sensitive switches, which do not depend on mechanical action to actuate them, may provide more durable alternatives to quick-break technology.