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Circuit symbol for a dimmer

A dimmer is a thyristor controller or triac controller for controlling the brightness of incandescent lamps such as stage spotlights, lights or transformers for low-voltage halogen lamps.

Under certain conditions, dimmers can also be used to control the power consumption of other consumers; Similar circuits can be found, for example, in vacuum cleaners or hand drills in which the power is to be changed (see also the article on soft start ) .


Circuit for dimming by means of phase control. The brightness of the incandescent lamp La can be changed via P.

There are different types of dimming depending on the load characteristics. Incandescent and high-voltage halogen lamps (230 V) as well as conventional transformers are dimmed with phase control . These consumers have an ohmic or an inductive load characteristic. Electronic transformers in low-voltage halogen systems have a capacitive load behavior and must be controlled with phase dimmers that are more complex in terms of circuitry . There are also universal dimmers, the electronics of which recognize the load characteristics and automatically set the appropriate control method.

Fluorescent tubes and other gas discharge lamps cannot be dimmed in this way, since the discharge collapses at low voltage and cannot be re-ignited. Even before the discharge is interrupted, the cathodes no longer reach the required temperature in the event of undervoltage and wear out more quickly. Electronic ballasts (EVG) with brightness adjustment are used here, which guarantee the required cathode temperature and generate a higher frequency and thus prevent the discharge from breaking up. The devices can be dimmed with a control signal (0… 10 Volt, KNX , DMX 512 , DALI ).


A dimmer can be controlled in various ways. In addition to the well-known rotary control , modern devices can now also be controlled using buttons. In the case of a remote push button dimmer, a short button switches the dimmer on and off, a longer button pulse causes a change in brightness. Activation by a control voltage is also possible in some cases; in such dimmers the control input is galvanically isolated from the mains.

Dimmer in professional lighting technology

Dimmer for 2.4 kW in the field of theater lighting

Via a control signal (as with DMX ) the devices are sent a value for each channel from the lighting mixer . With DMX this is usually a value from 0 to 255. The dimmers control the headlights according to this signal. Depending on the structure, the dimmers are located directly on the headlight housing or together or in groups in a rack . The connection to the headlights is then made via load multicores , also known as Laka (load cables). Often there is a switch field ( patch field ) between dimmers and lakas to allow different assignments of the multicores.

Stage lights are often not switched off completely, but only dimmed down until it is dark, so that the inrush current is lower when driving up to full power and the filaments are not so heavily loaded. With most dimmers, this can be made possible by a pre-heat function.

Household dimmers

In the living area there are dimmers in different shapes

  • permanently installed in lights
  • for installation in elements of the electrical installation , such as B. switch boxes etc.
  • for installation in rail-mounted distributors as rail-mounted devices (REG)
  • as so-called cord dimmers in front of mobile lights

Not every light source can be dimmed in its luminosity. The symbol for dimmability is a lying filled triangle with one or two letters underneath. Dimmers are also marked accordingly:

  • C for dimming with or for trailing edge dimmers (capacitive load, e.g. electronic low-voltage halogen lamp transformers or suitable LED lamps).
  • L for dimming with or for leading edge phase dimmers that are suitable for inductive loads (for example wound, i.e. conventional low-voltage halogen transformers).
  • R or ⨂ Incandescent lamp symbol : only resistive loads (incandescent lamps, heaters) can be dimmed with these dimmers.

power consumption

Course of the output voltage of a phase gating dimmer at almost full power
Course of the output voltage of a leading edge dimmer (dimmed)

If a normal incandescent lamp is dimmed, the power consumption and consequently also the energy requirement decrease. The service life increases, u. U. essential, since the filament temperature drops; however, the efficiency of light generation ( luminous efficiency ) drops sharply. When dimming, the brightness decreases more than the power consumption (see also luminous efficacy and service life of incandescent lamps ). Since the color temperature drops as a result of dimming , the light color also changes from white-yellow to yellow-orange.

Even with halogen lamps , which are a little more economical compared to incandescent lamps, the power consumption and consequently the energy requirement when dimming down also decrease. In dimmed operation, however, the service life only increases in the performance range of around 99 to 80 percent. In the dimming range of 20 to 60 percent, however, the tungsten-halogen cycle breaks down , which only deposits tungsten atoms on the filament again at temperatures above 250 ° C. The service life is significantly reduced because the halogen lamp behaves like a normal incandescent lamp without this rebuilding process.

If an incandescent or halogen lamp, such as a living room floor lamp, is never operated under full load anyway, a large part of the required energy can be saved if it is replaced by a weaker lamp that has the same brightness when not dimmed.

The efficiency of a fluorescent lamp, on the other hand, remains almost constant (or even increases) if it is dimmed with a suitable electronic ballast (EVG). This means that the power consumption decreases with the brightness to the same extent. The color temperature also remains largely constant.

Interference suppression

By the abrupt switching in phases to cut dimmers and switching off in phase from cut dimmers arise very steep flanks in the flow of current or voltage. According to the Fourier transformation , these edges correspond to a high-frequency frequency spectrum ( harmonics ), depending on their rise or fall time ( slew rate ), which can interfere with other devices such as sound and video systems. To reduce this interference, snubbers , chokes and filters are used to limit these steep slopes. Since these filters are expensive and heavy, interference suppression is one of the quality features of a dimmer.

You can find dimmers with almost no interference suppression (mostly household appliances with low power), dimmers for event equipment (rise times in the range of a few 10 microseconds) and devices for use in recording studios and theaters with rise times of 500 microseconds and more. The better the filter, the greater the rise times, which means that the high-frequency interference components decrease.


  • Michael Ebner: lighting technology for stage and disco; A handbook for practitioners. 1st edition, Elektor-Verlag, Aachen 2001, ISBN 3-89576-108-7 .
  • Michael Ebner: lighting technology for stage and disco; A handbook for do-it-yourselfers. 6th edition, Elektor-Verlag, Aachen 1992, ISBN 3-928051-12-1 .
  • Hans R. Ris: Lighting technology for practitioners. 2nd edition, VDE-Verlag, Berlin Offenbach 1997, ISBN 3-8007-2163-5 .
  • Wilhelm Gerster: Modern lighting systems for indoors and outdoors. 1st edition, Compact Verlag, Munich, 1997, ISBN 3-8174-2395-0 .
  • Günter Springer: Expertise in electrical engineering. 18th edition, Verlag Europa-Lehrmittel, Wuppertal 1989, ISBN 3-8085-3018-9 .

Web links

Wiktionary: Dimmer  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. Archived copy ( memento of the original from November 29, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Dimmability letters @1@ 2Template: Webachiv / IABot / www.merten.de
  2. Philips Lighting Online Academy ( Memento of the original from October 16, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 1.4 MB) accessed on April 17, 2012.  @1@ 2Template: Webachiv / IABot / www2.philips.de