How does dimmer work?

We are often asked about the subject of “dimming LED lamps and LED strip lights“. How LED Controllers can conveniently control with an LED remote control or a mobile phone app. That’s why we want to go into a little more detail in this article. 

1.Dimming of LEDs
2.What types of dimming are there?
3.How are LEDs dimmed?
4.In which dimming range should a luminaire work?


The dimming technology was based on alternating current/voltage (AC) operated
Ohmic (R – resistance) consumers
Inductive (L-coil) consumers
Capacitive (C – capacitor) consumers

The LED, on the other hand, is a semiconductor element operated with direct current/voltage (DC). Signals from existing dimmers are therefore used to dim LEDs to adapt the non-linear current-voltage characteristic with electronic circuits. 

There are different types and options for dimming:

Voltage Regulation via a Variable Resistor

A controllable load resistor (series resistor) is simply connected in series with the lamp. In this way, the brightness can be regulated continuously from 0 to 100 percent. The more voltage dropped across the resistor, the more it would be dimmed. Nevertheless, this principle would be completely unsuitable for practice, because it has one major disadvantage. The adjustable resistor would become very hot during operation and, including the necessary measures to dissipate this heat, could never be integrated into the usual format of a dimmer. Besides, this method would be a complete waste of energy, because the useless heat generated by the dimmer would literally “burn up” and would have to be paid for with the electricity bill.

Dimming with Pulses or With Oscillation Packages

To avoid the above-mentioned disadvantage of the high energy consumption of series resistors, not all sinusoidal oscillations of the alternating current are led to the luminaire when using pulses. This gives the pure sinusoidal oscillation and would save energy and dim it, since not all of the electrical energy reaches the lamp. The disadvantage of this method is that the constant heating and cooling of the filament cause flickering and so no fine dimming is possible.

Dimming with Phase Control

With the principle of phase control, each sine half-wave (positive and negative) is cut at the beginning, so that only the rear part of the wave is used energetically. The current flow is controlled by a so-called Triac (antiparallel connection of two thyristors). The dimmer or Triac blocks the flow of current to the lamp until it receives an ignition pulse. From this point in time (this “phase” of the alternating current signal) the consumer is supplied with energy until the next zero crossings. The later the triac is ignited, the lower the average power. The leading edge dimmer is, thanks to its extremely low power loss, the most widely used dimmer circuit. This type of circuit cannot be used for capacitive (C) loads, as here because of the sudden increase in voltage, an extremely high current would flow.

The phase section control is the opposite of the gate control. The current is switched on immediately after the AC voltage crosses zero. As soon as the required power is reached, the sine wave is cut off and the current flow is interrupted. This type of circuit can not be used for inductive (L) loads due to the voltage spike when the current is switched off.

Dimming with Leading Edge and Section Control

This principle represents a combination of the two previous methods. Due to the higher power dissipation and the non-existent possibility to switch inductive as well as capacitive loads, this control is not used in practice.

Dimming with IPS

Here the principle of phase control and phase control is used in combination. The term “IPS” was coined by the manufacturer. In contrast to the original phase control, switching on and off is no longer abrupt, but rather via an IGBT (Isolate Gate Bipolar Transistor). This creates a slowly rising or falling ramp. Versions of this universal dimmer are available both as phase control and phase control.

Dimming with Pulse Width Modulation(PWM)

With pulse wide modulation, in German pulse-width modulation, PWM for short, the power source is switched on and off via a PWM signal with a low frequency. Please note, however, that the LED driver cannot switch immediately, which has two consequences. When switching on, there is a certain reaction time until the output current is present, and when switching off there is a delay because the output capacities still have to be discharged via the LED circuit. With the help of the PWM principle, it is possible to control the load types R and L in terms of power. Here, the sine curve ensures that the current flow gently increases and decreases in accordance with the sine shape, thus eliminating harmonic waves. In this way, the light sources are particularly protected. Unfortunately, this principle has the disadvantage that high-frequency flickering can occur when dimming LEDs. This can lead to interference with other discontinuous light sources such as TV or computer monitors and cause stroboscopic effects. There is also the risk of epileptic seizures and headaches.

Dimming with A 0-10 Volt Control System

These systems are based on a proven industry standard for electronic ballasts according to IEC 60929. Although they are mainly used in energy management, eg together with motion or daylight sensors, they are also suitable for controlling LEDs. The 0-10 volt controllers are insulated from live cables and can therefore be touched without danger and simply wired up.

Dimming with the Dali System

The Digital Addressable Lighting Interface Protocol was originally developed in Europe but is now used worldwide. Since it allows the digital control of individual light fixtures and thus a high degree of fineness in the control, it is often used in commercially used buildings or wealthy private households. To control LEDs with DALI, you need LED drivers or ballasts that can process this technology.

Dimming with DMX Control Device

With DMX control devices you can control 512 different functions. The functions of the DMX control are based on channels such as brightness (dimmer), color or direction of light (pan and tilt). The signal is particularly suitable for controlling and dimming RGB-LED applications, as these benefit from high speed and the number of channels.

Dimming with KNX

KNX is a bus system for building automation and is used to intelligently network a wide variety of electronic consumers. Lighting, shading, heating, air conditioning, ventilation, alarm, information, remote access, central house control and much more can be controlled using KNX. interconnect integrated. Example: Instead of a light switch, the switch-on command for lighting is given cumulatively via sensors. At dusk, a light sensor measures that the light intensity in the room is decreasing. Therefore he gives the order to the ceiling lights to switch on. He could also let the ceiling lights become continuously brighter. When the sun has completely set, the lamp shines with maximum brightness. With this continuous dimming, the room would be kept constantly bright. If there were several ceiling lights in the room.

How are LEDs dimmed?

To control the brightness of an LED in a controlled manner, the change in the current must be based exactly on the non-linear current-voltage characteristic of the light-emitting diode. The LED is a diode and initially reacts only minimally or not at all when the supply voltage increases. Only when the forward voltage is reached does the current and thus the light yield rise steeply. Dimming in the same way as a light bulb would therefore have to result in a completely different correlation between the input variable (position of the control potentiometer) and output variable (light output of the LED).

In practice, the brightness of LED lighting is therefore usually not controlled directly via the dimming process described. Instead, in modern dimmable LED power supplies, the signal from a phase control is converted into a control current with the help of an evaluation circuit, the level of which determines the brightness of the LED. This direct current is constant over time and is decoupled from the mains frequency, which is why a ripple of the light intensity cannot arise in the first place. This functional principle also applies to pulse-width modulation (PWM).

The following must be observed in connection with the dimming of LEDs:

  • Direct current dimming changes the light color of the LED – that is, the light color is often shifted into reddish in the color triangle.
  • Dimming improves the LED efficiency – as the junction temperature decreases due to the lower current flow, the efficiency increases.
  • Dimming improves the service life of the LED – because it is operated at a lower temperature, the service life of the LED increases

In which dimming range should a luminaire work?

An incandescent lamp can be dimmed below a light intensity of one percent of perceived light. That is just enough that the glowing orange wire in the lamp can be seen with the naked eye. LED lamps, on the other hand, achieve different light intensities: For example, one LED lamp can be dimmed to around 50 percent of the perceived light, while another can be dimmed to 10 percent. As a result, not every LED is suitable for every application.

When selecting the LED, it should be noted that the LED manufacturers usually do not indicate the dimming ranges of their products in terms of the light intensity perceived, but rather the intensity of the measured light. This is important to know because the human eye works logarithmically. This is because, on the one hand, people have to be able to handle very bright light, as it is on a sunny summer day, for example. Here we are quickly at 100,000 lux. On the other hand, we can see under moonlight, which corresponds to about 0.25 lx.

That is why we usually perceive light sources as being brighter than the packaging labels suggest. Measured light of 20 percent, for example, corresponds to 45 percent perceptible light intensity. To avoid bad purchases, the following formula could help: The perceived luminous intensity of a luminous body is equal to the square root of its measured luminous intensity: Example √0.2 = 0.45.

Dimming of warm white, cold white, and RGB or RGBW LED strips
To dim the LED strips from LED Universum, we offer RGB LED Controller, and RGBW LED Controller that you can conveniently control with an LED remote control or a mobile phone app.

What should be considered with 230V dimmers:

Not all light sources can be controlled with every dimmer. When purchasing, the following points should be observed to ensure the greatest possible compatibility.


Many dimmers work in a specific work area, which is specified accordingly. There are two entries for the work area:
Dimming range:
This is often given in percent as a range. E.g. 0% – 100%. This means that a connected light source can be dimmed from 100% maximum brightness down to 0% brightness. This information is only meaningful in connection with the wattage.

The wattage tells you what power a dimmer can do. Usually, two values are also given. A maximum performance as well as a minimum performance. E.g. 50W – 300W. The maximum power indicates how many watts can run through the dimmer. The total output of all lamps controlled by a dimmer should not exceed the maximum output. The minimum power indicates the wattage down to which the dimmer can be dimmed. With a dimming range of 50W – 300W, lamps with a maximum total power of 300W can be connected, which can be dimmed down to 50W. To control LED lamps, it is always advisable to select a dimmer with a minimum power of 0W to be sure.

LEDs convert electricity into light with the help of semiconductor material. This method of generating light is very efficient and ensures that even low currents are sufficient to make LEDs glow. It is therefore advisable to only use dimmers for LED lamps that have a proper display and thus completely separate the lamp from the line. In the case of dimmers that dim down to 0% and are equipped without an additional off position, they are switched off by an electronic component. However, this does not completely block the line but still allows low leakage currents to pass. These low currents ensure that the LED light source still glows slightly. The glow is usually not visible.

Type of Dimming:

With AC dimmers, there are three common ways of dimming a lamp:

  • Phase section dimming
  • Leading edge dimming
  • Dimming with pulse

These dimming variants are summarized under the English term TRIAC. Most commercially available dimmers (e.g. from Gira, Siemens, Eltako, ELV, or Mertens) can implement all three dimming variants. When purchasing, it should be ensured that the light source and dimmer can process at least one dimming process in the same way.

Note: For direct current lamps, other methods such as pulse width modulation (PWM) are used for dimming.

Effects When Dimming:
Whether a lamp and a dimmer are ultimately compatible and good dimming results can be achieved cannot be determined 100% exactly, despite the comparison of the specifications of the dimmer and LED lamp. Often dimmers and lamps have to be tried out together. The following phenomena can occur when operating an LED light source with a dimmer:

LED light source flickers when dimmed (aliasing effect):

When dimming down, the sine curve of the alternating current is changed. In brief moments, this change creates an operating state that cannot be processed by the electronics of the LED light source. This leads to flickering. AFTER setting the desired dimming value, the LED illuminant lights up constantly at the desired brightness level.

At a certain dimming level, the LED light source flickers or goes out completely:
Dimmers and lamps are not completely compatible. The dimmer can dim into an area that the lamp cannot process. This can be caused, for example, by incompatible dimming methods or by dimming down too far. This occurs when the light source cannot be dimmed down to 0%. Another cause may be the modification of the sinusoid. With phase segment dimming, part of the sinusoidal curve is “cutaway”. This targeted power interruption reduces the average power supply for the lamp. The lamp can start to flicker if the “cut-off” area becomes too large.

Dimming does not run constantly :

The dimming curve of dimmers can run differently. Depending on the construction, this can decrease linearly or in a parabolic function. This has the effect that the brightness of the light source is regulated at different speeds depending on the dimming position. With a 100% compatible dimmer, the brightness is set evenly.
LED glows despite being switched off :

The dimmer switches to the “Off” operating state via an electronic component. This component does not completely separate the line but allows a small control voltage to pass through and puts the lamp into standby mode. With conventional lamps, these leakage currents are too low to make the lamp shine. However, LED lamps can process these currents and a slight glow is created. This can only be turned off by using a dimmer with a complete power cut-off, for example using a toggle switch.

The lamp is switched off, but it flashes regularly :
With lamps that are operated via an LED driver or an LED power supply unit (e.g. LED panels or LED recessed spotlights, recessed floor spotlights, flush-mounted lights) it can happen that they flash at regular intervals when dimmed down to 0% and thus “switched off”. This is caused by the dimmer. The dimmer switches to the “Off” operating state via an electronic component. This component does not completely disconnect the line but allows a small control voltage to pass and puts the lamp into standby mode. If the lamp has a power supply unit (or transformer), the leakage current continuously charges the capacitors built into the power supply unit. As soon as sufficient energy has been collected in the capacitors, the downstream electronics in the power supply unit are supplied with energy, and these are passed on to the light source, which then lights up accordingly. Since the energy is used up quickly by the light source, the light source switches itself off again after consumption.

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