Dimming

The lighting system is designed to provide the maximum required illumination, although in many situations this is not actually necessary.

Alongside quantity, a higher quality of light is increasingly appreciated; for this, it is necessary to overcome the traditional concept of control which only allows switching on and off.

The light intensity emitted by the lighting fixtures can be controlled thanks to dimming, individually or in groups, and this can satisfy different needs: for example, greater visual comfort, providing exactly the amount of light needed where and when required. In other cases, dimming is useful when there is great availability of natural light that can be exploited, reducing the component of artificial light.

Where non-negligible power requirements or long turn-on/ turn-off times are at stake, the brightness control is also effectively used to save energy and extend the useful life of light sources and electronic components: this is the typical case, for example, of office environments or production areas.

Traditional techniques

Leading edge phase dimmers reduce the current flow that feeds the load; for a long time this technique has been used for the dimming of incandescent and halogen lamps. For this purpose, the power supply wiring of the lamps is used; due to the ban imposed on these sources by many countries (in the EU starting from the Commission Regulation 244/2009), this type of dimming has rapidly decreased in importance.

The 1... 10V analog interface represented another very common technique in combination with fluorescent tubes and dimmable electronic ballasts (EVG) equipped with the appropriate interface. In this case, the reactor supplies the control voltage which can be modified by means of a regulation device based on the variation of the electrical resistance; for this purpose, a separate additional electrical connection is required, while the switching on and off takes place through the connection of the 230 Vac power supply network.

The arrival of bus systems for building automation has made it possible to use actuators / dimmers, with dedicated 1 ... 10V control outputs, and to connect them to the network for group controls, lighting scenarios and coordinated operation with other functions.  

The diffusion of digital communication interfaces on board of the lighting bodies - in particular those with DALI standard - is reducing the use of the 1 ... 10V dimming technique

Hue and colour adjustments

LED lamps have quickly become the most popular light sources on the market. They offer a range of control options that were previously difficult to implement, such as warm/cold white light and colour control. Applications that reproduce the colour temperature variation characteristic of natural light in indoor environments, such as HCL control, have become possible at very affordable costs. There is a difference in control between the modes:

• DIM TO WARM: with the “dim to warm” control the colour of the light becomes warmer as the brightness is reduced;
• TUNABLE WHITE: With the “tunable white” control the brightness and colour of the light are set separately.

Special features of LED sources

From a technical point of view, LEDs are ideal to dimming, a feature that is not true for all light sources, as in the case of discharge lamps.

However, there are different types of LED sources such as:

• LED lamps without integrated driver;
• LED lamps with integrated driver and 230 Vac mains voltage power supply;
• LED lamps with integrated driver, very low voltage power supply (12 / 24V).

Only some of the most common control systems are automatically suitable for dimming LED lamps: to define the most suitable solution, it is therefore always necessary to check in advance the compatibility between sources and control devices.

The LED sources can be dimmed either by analog dimming by adjusting the current or by using the PWM technique (pulse-width modulation). In the latter case, the current flow through the LED is interrupted rhythmically with a certain frequency. The greater the intervals between the current delivery phases, the lower the actual and average current through the LED and therefore the perceived brightness.

PWM frequencies higher than 300 Hz are not perceptible to the human eye and therefore no flickering is noticeable, despite a modulation in progress.