About phase-pulse control (impulse)

Phase-pulse control is a simplified and economic version of light control, using controllable HF-ballasts designed for this function. Normally, these ballasts can also be controlled via a bus system such as DSI, DALI or 1–10 V DC depending on the brand and type. However, the functions cannot be combined as this can result in considerable damage.

Phase-pulse control does not require a regulator or other controller, the signal to the HF-ballast is obtained directly from a simple momentary switch. Other additional modules are not required. In effect, the regulator is integrated in the HF-ballast.

Only a four core cable to the luminaire is needed: Direct (unswitched) mains voltage, neutral and protective earth as well as the mains voltage (impulse) via the momentary switch.

Phase-pulse control is also an ideal system when you want to control a lighting system from several places in the room. Reliability lies in its simplicity and the lack of intermediate units means installation is easy and inexpensive.

Control switches can comprise of 250 V switches with normally open contacts and impulse springs, or switches with a return spring. When using such a switch, the luminaire is turned on and off by quickly pressing and releasing the switch, while adjustment of the illumination level, alternating up and down, is performed by pressing and holding down the switch.


  • Control switches must not be equipped with indicator lamps, as the leakage current from these cause malfunctions.
  • The maximum length for the control cable is normally unlimited as the signal is a 230/240 V signal impulse.
  • The same phase should be used for control as well as the power supply to the luminaire. This produces an unpolarised connection, which means that the luminaire can also be equipped with a plug. A 3-phase connection is also possible, but this requires a special polarised connection.
  • Simultaneous use of phase control (impulse) and another control method such as DALI or DSI will cause irreparable damage to the digital control equipment.
  • Avoid mixing different brands in the system.

Phase pulse control can sometimes end up out of phase. This is often due to how the impulse switch is used. Some users press the button very briefly, and only some of the HF ballasts perceive this as a signal to adjust.

Every brand has a different method of getting the lighting back into phase. It is usually sufficient to keep the impulse switch pressed down, thereby adjusting all luminaires to “on” mode. Adjustment is then performed as normal.

This phenomenon can also occur if there are a lot of mains harmonics which interfere with operation. In this case, the simplest thing to do is to replace the push button with another type of control. Fagerhult recommends another method of regulation when controlling more than four HF ballasts because of the out of phase problem and because harmonics can impede proper functionality. Use DALI HF ballasts and an Osram MCU (86212) rotary potentiometer instead.

Absence dampening – new function

The new HF-ballasts from Tridonic PCA ECO and Excel can also be used for dimming between a high level (occupancy) and low level (absenteeism) via occupancy detectors. A perfect function for stairwells, corridors and culverts. Large amounts of energy can be saved in this way, without extinguishing the light completely.