Page 177 - Advanced Course

KNX ADVANCED COURSE

5 Brightness Control

5.1 Areas of Application, Objective

In contrast to lighting control in which you wish to achieve individual and optimum levels of
light intensity as mentioned above, brightness control is mostly considered with regard to
minimising installation costs without fully losing sight of the goal of reducing energy costs.
It is however agreed between the planner and user that significant deviations from the
setpoint/actual value can occur in the control system. This is particularly the case when
only switchable lamps are integrated in the control system.

Figure 13: Principle of brightness control

5.2 Types of Open-loop Lighting Control

For brightness control, a distinction is made between continuous control and two-step
control. A sensor measures an external brightness value which is independent of the
internal illuminance that is to be set. Starting from this measured value, the internal control
value is determined at first via any calculation function which the room illuminance uses to
reach the required setpoint. Technically this is an open control loop. The feedback loop is
missing. This has both advantages and disadvantages. It is beneficial that this type of
lighting control can never oscillate since the feedback loop has been omitted as
mentioned. Starting with the measured value of a single sensor, many different control
curves can be differentiated. The disadvantage is that a very extensive adjustment must
be carried out for continuous control which takes at least one day.

5.2.1 Continuous Control

Continuous control – like the closed-loop control above – requires dimmers or dimming
actuators which can be infinitely adjusted. As an automatic adjustment of the control value
cannot take place (due to the missing feedback loop), this must be carried out by selecting
a control function. In the simplest case, this can be a straight line determined by two pairs
of values: a) maximum external brightness above which there should be 100% interior

Home and Building Management Systems KNX Association
Lighting Control Lighting Control_E0310a.doc 18/34