Page 164 - Advanced Course

KNX ADVANCED COURSE

Light strip 1 Light strip 2 Light strip 3

~ 26 % ~ 48 % ~ 70 %
Receiver Receiver Receiver

500 lux required light intensity

Necessary
artificial light

Existing daylight

Goal: Brightness control optimised for all areas of the room

3 Principle

Closed-loop and open-loop lighting control systems are based on the modulation of the
lighting level inside the room by the measurement of either the level of external light
(independent variable) or the measurement and feedback of the level of internal light
(dependent variable) which contains a variable proportion of external light. In both
variants, the primary goal is to maintain a required level of internal light as constant as
possible. In general, it is a feature of a distributed system such as KNX that the individual
tasks in the closed-loop or open-loop control systems are distributed among different
devices: sensors, actuators and controller modules. This has both benefits and
disadvantages as outlined below in detail.

4 Constant Lighting Control

A closed-loop control circuit is used for constant lighting control. The required level of
brightness in the room or the level of lighting at the desk is measured as a controlled
variable together with the interference from the external light and then fed back to the
actuators in the appropriate manner.

Controlling system Controlled system Z

W Controller Y Actuator Contr. variable X
- +
X+Z

Measuring device
Brightness
sensor

W ... Reference variable (e.g. brightness, setpoint) Z ... Interference (level of external light)
Y ... Control value (dimming value 1-100%) X ... Actual value (lux value at workstation)
Figure 1: Constant lighting control

Home and Building Management Systems KNX Association
Lighting Control Lighting Control_E0310a.doc 5/34